Forest ecosystems change along fertility gradients, both at large climatic scales and locally, depending on mineralogy and hydrology. Changes in vegetation communities and traits along fertility gradients have been studied thoroughly, but corresponding changes in soil fungal communities are less well understood. In boreal coniferous forests, ectomycorrhizal fungi play a pivotal role, not only in tree nutrient uptake, but also in decomposition, and interact with free-living saprotrophs in complex manners.
We conducted DNA-based analyses of soil fungal communities in a national forest inventory across Sweden. In a local fertility gradient, we analysed fungal decomposer traits by metatranscriptomics. In the national data set, changes in relative abundances of fungal guilds were assessed in almost 1600 sites along climate and soil fertility gradients. In the local study we sequenced mRNA from composite samples of the organic horizon in 16 plots with contrasting N content, pH and tree species. We specifically targeted expression of genes coding for cellulolytic and oxidative enzymes and analysed responsible fungal taxa.
The abundance of free-living saprotrophic basidiomycetes with well-developed capacity to decompose recalcitrant organic substrates (e.g. Mycena species) declined in colder climate and in more acidic and nitrogen-poor soils. In the metatranscriptomes we found reduced expression of basidiomycete cellulase genes and indications of supressed growth of basidiomycete saprotrophs under more acidic and nitrogen poor conditions. In contrary, ectomycorrhizal species with well-developed oxidative enzyme systems, mainly members of the genus Cortinarius, increased in relative abundance towards colder climates and nitrogen-poor soils. In the metatranscriptomes, mycorrhizal Cortinarius species accounted for 60% of gene expression of extracellular peroxidases, which are central for decomposition in the boreal forest floor that is rich in lignin, melanin and tannins. Overall expression of peroxidase genes was upregulated in unfertile pine plots relative to more fertile spruce plots.
Altogether, we see indications that saprotrophic basidiomycetes are severely hampered by the harsh conditions in the organic horizon of boreal forests and have major problems to maintain their role as major decomposers. When the saprotrophs fail, decomposition is instead maintained by certain ectomycorrhizal fungi, who use their direct supply of carbon from the tree roots to drive oxidative decomposition, presumably liberating tightly bound nutrients for themselves and their hosts. In line with this hypothesis, unfertile conditions trigger increased investment in oxidative enzymes. The mycorrhizal link between living roots and decomposition implies that organic matter turnover in boreal forests may be largely controlled by the trees, analogous to a strong and direct priming effect.
How to cite: Lindahl, B., Barbi, F., Clemmensen, K., Dahlberg, A., and Stendahl, J.: Ectomycorrhizal fungi take over decomposition when saprotrophs fail, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-15380, https://doi.org/10.5194/egusphere-egu25-15380, 2025.
In forest ecosystems, the forest floor acts as a boundary between the mineral soil and the atmosphere, serving as a hub for microbial nutrient turnover and transport. The forest floor is stratified and comprises several distinct layers characterized by successional changes in properties like nutrient quality, oxygen content or rate of disturbance. How microbial community development follows changes in chemical forest floor properties is not studied so far. This study aims to characterize the microbiome and identify key-stone taxa of the forest floor at a fine vertical resolution across temperate, beech-dominated forests.
Forest floor samples were collected from three German beech-dominated forests differing in climate and soil phosphorus content, spanning eight distinct layers of the forest floor and topsoil profile (OL0, OL1, OLF, OHF, OH, A (0-5 cm), A (5-10 cm), A (10-20 cm)). Prokaryotic community composition was analysed using 16S rRNA gene amplicon sequencing. Layer-specific keystone taxa were identified by finding taxa shared across the sites and evaluating their impact on SpiecEasi based cooccurrence networks. Community assembly processes of each layer were assessed through b-NTI analyses. Additionally, total elemental concentrations were measured by ICP-OES.
A clear stratification of the forest floor microbiome was observed. Proteobacteria and Bacteroidota dominated the litter layers but declined with depth, whereas Acidobacteria and Chloroflexi became more abundant with depth in the forest soil profile. Redundancy analysis revealed that layer-specific physicochemical parameters, such as total carbon, nitrogen, and pH, had a strong influence on microbiome composition, with sulfur, calcium, potassium, iron, and aluminum also significantly impacting microbial community composition. Generally, the impact increased with depth. We found a set of key-stone taxa specific for each forest floor layer and present at every site, each with a combined contribution between 10 and 20% of the total layer microbial abundance. Differences between the microbiomes of the three forest sites based on bray-curtis distances were most evident in the fresh litter layer and the mineral horizons, while the microbiome in the fragmented and humic layers was more uniform. This is further confirmed by community assembly analysis, which showed that homogenizing selection became more pronounced with progressing litter decomposition.
The vertical stratification of the forest floor is mirrored closely by microbial community composition and assembly. Each layer comprises different niches, which are formed by changes in substrate quality, and support distinct key-stone taxa. Compositional differences between forest sites are likely based on climatic conditions and bedrock type, whose influence is biggest at boundary layers like fresh litter and mineral soil, respectively. Similar successional trends of the microbiomes and high abundance of shared taxa were found between the sites, suggesting that litter type could be the primary driver of the forest floor microbiome composition. These findings enhance our understanding of how vertical stratification and substrate quality influence the forest floor microbiome.
How to cite: Bibinger, S., Villalba Ayala, G., Prietzel, J., Schloter, M., and Schulz, S.: Microbial Diversity and Keystone Taxa in the Stratified Forest Floors of Beech Forests, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-4802, https://doi.org/10.5194/egusphere-egu25-4802, 2025.
The forest floor (FF) serves as the critical interface between the aboveground and belowground components of forest ecosystems. It plays a pivotal role in regulating water and energy exchange between the atmosphere and the soil, providing habitat for roots and diverse soil organisms, mitigating soil erosion, and promoting tree growth in forest ecosystems. Forest floors buffer harsh environmental conditions and insulate soil, thereby mitigating the effect of climate extremes on soil fauna. Conversely, the soil fauna is key for shaping the structure of FFs. Considering the recently documented decline in FFs across Europe, changes in the composition and activity of soil animal detritivores and their consequences for changes in the structure of FFs need closer attention. Unfortunately, the structure of decomposer animal communities across different layers of FFs and their variation with soil nutrient status and climatic factors has not been comprehensively investigated. We investigated the distribution patterns of two major decomposer microarthropod groups (Collembola and Oribatida) across the different layers of the FF (Ol, Of/Oh and Ah) of 12 forest sites representing temperature and phosphorus gradients. A total of 58 Collembola and 144 Oribatida species were recorded. Phosphorus as main factor neither significantly affected the abundance of Collembola nor that of Oribatida. The same was true for the effect of temperature on the abundance of Collembola, whereas the abundance of Oribatida varied significantly with temperature. Further, Oribatida richness significantly increased with increasing temperature but decreased with increasing phosphorus level. The effect of layer was highly significant for both Collembola and Oribatida. Specifically, the abundance, richness and biomass of both microarthropod groups was at a maximum in the Of/Oh layer followed by Ah and Ol layer. Collembola and Oribatida community structured varied with temperature and phosphorus levels but in both this depended on layer. Soil and litter carbon-to-nitrogen ratio, pH, Gram-positive bacterial phospholipid fatty acids (PLFAs) and thickness of Ol and Of/Oh layers were identified as major drivers. The results suggest that the distribution and community composition of Collembola and Oribatida are intricately linked to both biotic and abiotic factors in the FF. These findings highlight the critical influence of temperature, phosphorus and FF stratification on soil microarthropod communities, alongside additional soil chemical, microbial and physical characteristics of the FF. The differential responses of Collembola and Oribatida to temperature and phosphorus gradients underscore functional and ecological differences between these groups, with Oribatida displaying a stronger sensitivity to climatic and nutrient changes. Overall, the results emphasize the importance of maintaining the structural integrity of forest floors to support diverse and resilient soil fauna communities.
How to cite: Chen, J., Rocaboy, A., Junggebauer, A., Lu, J., and Scheu, S.: Depth-dependent dynamics of microarthropods in forest floors: interactions with temperature and phosphorus levels, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-3178, https://doi.org/10.5194/egusphere-egu25-3178, 2025.
Root exudation is a key process for plants to acquire nutrients. This process works directly, or indirectly through the microbiome priming effect. Likewise, plants release a significant amount of carbon into the soil, which stresses the importance of root exudation for carbon cycling. Nonetheless, detailed data on root exudation, especially compound-specific data from forest trees are scarce, but urgently needed. Recent studies suggest a high importance of the forest floor for nutrient acquisition, which is therefore of special interest for studying root exudates.
In this study, we sampled root exudates of Fagus sylvatica, Picea abies and Acer pseudoplatanus at four temperate forest sites with varying mean annual air temperature, annual precipitation sums and soil phosphorus (P) levels. Samplings took place in spring and autumn and in two soil depths: the forest floor (surface layer of the forest soil with ≥ 15% organic carbon) and the upper mineral soil (A5 horizon). Root exudates were collected using an in-situ cuvette-based approach. For this purpose, living tree roots were cleaned, and after a period of recovery, incubated for 24 hours in a cuvette filled with glass beads and a nutrient solution. Compounds in the retrieved solution were analysed by a mass spectrometer coupled to a gas chromatograph.
81 compounds were included in the analysis and divided into functional groups. All studied species showed higher exudation in spring compared to autumn with a higher share of amines in spring. Differences in exudation patterns between species could be detected for the two soil depths: While F. sylvatica showed a higher exudation in the forest floor, P. abies and A. pseudoplatanus exuded more in the mineral soil. This pattern is expected for F. sylvatica and A. pseudoplatanus, since F. sylvatica, which usually is associated with ectomycorrhiza (ECM), is said to follow an organic nutrient strategy and A. pseudoplatanus, which usually is associated with arbuscular mycorrhiza (AM), is said to follow an inorganic nutrient strategy. However, the behaviour of P. abies usually being associated with ECM and therefore following an organic nutrient strategy is in contrast to what literature suggests. A site-species-interaction effect was found with increased exudation on P-poor sites with low temperature for F. sylvatica, and with high temperature for P. abies and A. pseudoplatanus.
Facing a thinning of the forest floor with globally increasing temperatures, studying root exudation can indicate the forest floor’s role for tree nutrition. Clear differences in root exudation in quantity and composition between species, seasons and soil depths urge the need for further research to elucidate the effect of site conditions on exudation patterns.
How to cite: Wannenmacher, M., Haberstroh, S., Kreuzwieser, J., and Werner, C.: Site, season and soil depth affect the composition of root exudates in three temperate tree species, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-10145, https://doi.org/10.5194/egusphere-egu25-10145, 2025.
Forest floors are the interface between vegetation and soil and are therefore often neglected by science. Wrongly so, because they are highly sensitive and integrative indicators of ecosystem processes and fulfil important functions. Using an interdisciplinary approach, we analyse the properties and functioning of organic layers at 12 temperate forest sites, dominated by European beech and differing in P-status and mean annual air temperature. In agreement with literature, we found increasing mass of FF with decreasing temperature and P availability in the mineral soil. However, we found no significant differences in FF mass and C stocks between calcareous (n=3) and silicate (n=9) sites. The range of FF properties found by far exceeds the range of mineral soil properties. The pH(KCl) values of organic layers (OF and OH horizons) varied between 2.6 and 6.6. The FF mass ranged from 17 to 81 t ha-1, the C-stock from 6.2 to 38.8 t ha-1, the C/N ratio from 16 to 44, the concentrations of citrate extractable P from 66 to 487 mg kg-1 and the cation exchange capacity from 186 to 634 µmolc g-1. Gross FF turnover calculated based on litterfall and FF mass ranged from 3.0 to 22.9 a. The fine root biomass showed close correlation with FF mass and precipitation at the studied sites. Cool and wet sites showed the highest root biomass. The identification and analyses of controlling factors and interrelationships with the microbial community and soil fauna at the study sites are currently in progress and will be presented. Based on the results obtained so far we conclude that the huge plasticity of European beech is mirrored by the heterogeneity of beech forest floor properties.
How to cite: Lang, F., Niederberger, J., Schilling, L., Scheu, S., Chen, J., Schulz, S., Schloter, M., Bibinger, S., and Prietzel, J.: European beech forests create an impressive diversity of forest floors, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-19450, https://doi.org/10.5194/egusphere-egu25-19450, 2025.
First-year seedlings, with nascent tissues and limited nutrient reserves, are much more sensitive to environmental stressors than mature trees. Seeds and seedlings rely on the forest floor (FF) as a source of water and nutrient supply while it harbours soil microbes that are both beneficial (e.g. mycorrhizae) and detrimental (pathogenic fungi) to early seedling establishment. Therefore, FF changes, along with and as a result of climate change, may have major impacts on tree regeneration success and composition, which have received little attention in forest research so far. Our greenhouse experiment investigates how changes in FF properties affect seedling establishment and growth of three Central European tree species differing in seed size: Fagus sylvatica (European beech), Acer pseudoplatanus (sycamore), and Picea abies (Norway spruce). We used FF material and mineral soil collected from three mixed European beech forest sites in Germany differing in soil P availability. Seeds were sown in December 2023, and seedling establishment and growth were monitored under different treatments (tree mixture; precipitation regime; application of fungicide; shredding of the FF) throughout one vegetation period before harvest in autumn 2024. Preliminary results indicate that shredded, fine-textured FF enhanced substantially the establishment rate of spruce in two out of three soil origins, while no consistent pattern was observed for beech and sycamore. This suggests that intact FF may act as a physical barrier for small-seeded species but is less mechanically impactful for species of larger seed size. The application of fungicides increased the establishment success of beech, indicating a significant impact of pathogenic fungi in FF. In terms of growth, broadleaved seedlings exhibited enhanced shoot length in phosphorus-rich soil, with sycamore showing a twofold increase and beech a 1.3-fold increase compared to phosphorus-poor condition. We also found that beech seedlings grown in monoculture achieved double the shoot length of those mixed with sycamore, indicating intense interspecific competition of sycamore under abundant light condition in the greenhouse. Interestingly, while fungicide application reduced length growth of both beech and sycamore in phosphorus-poor soil, it marginally improved growth in phosphorus-rich conditions, underscoring the importance of mycorrhizal associations in nutrient-limited environments. Further analyses are ongoing to assess the susceptibility of seeds and established seedlings to fungal infestations with changes in seasonal distribution of precipitation and to drought stress in dry periods. How soil nutrient availability mediates the growth responses to such factors will also be explored. These findings will deepen the understanding of the impact of forest floor properties on tree regeneration dynamics under changing environmental conditions.
How to cite: Doan, T. H., Kohler, M., and Bauhus, J.: The influence of forest floor properties on tree regeneration under changing environmental conditions, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-7587, https://doi.org/10.5194/egusphere-egu25-7587, 2025.
Northern forests are currently taking up large quantities of carbon due to forest growth. Yet, it is not known for how long the capacity of the soils to provide enough nutrients to support high forest growth will last. Therefore, it is important to understand nutrient dynamics in northern forests.
We analyzed 33,500 forest soils in Sweden in four repeated inventories covering the period 1983 to 2022.
During the four decades, the standing wood volume and the tree stem diameter increased by 15% and 29%, respectively, across all of Sweden. The plant-available magnesium (Mg), calcium (Ca), and manganese (Mn) concentrations of the organic layer increased continuously and significantly over the four decades across all of Sweden by 38%, 21%, and 100%, respectively. In the south of Sweden, where tree growth and biomass are highest, the Mg and Ca concentrations increased particularly strongly by 62% and 31%, respectively, over the four decades. The concentrations of plant-available Mg and Ca of the organic layer and their increases were related to properties of the mineral soil, such as soil texture and the Mg concentration of the parent material. Further, Mg and Ca concentrations of the organic layer were significantly higher and increased more strongly in broadleaf forests and spruce forests than in pine forests. The nitrogen (N) stock of the organic layer was highest in the second inventory, i.e., in the 1990s, and lowest in the fourth inventory. From the first inventory in the 1980s to the fourth inventory, the N stock of the organic layer decreased by 6% across all of Sweden.
Our results suggest that the increase in tree biomass and tree size caused an uplift of Mg, Ca, and Mn from the mineral soil to the organic layer, likely due to tree luxury uptake of these elements in the mineral soil. Furthermore, the N stock of the organic layer decreased over the last decades likely due to tree growth, after it was comparatively high in the 1990s due to high atmospheric N deposition. Taken together, the results indicate that strong nutrient uplift from the mineral soil occurred in response to forest growth and that N rather than base cations might become more strongly limiting for tree growth in northern forests in the future.
How to cite: Spohn, M., Karltun, E., and Stendahl, J.: Strong nutrient uplift associated with forest growth in northern forests, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-2846, https://doi.org/10.5194/egusphere-egu25-2846, 2025.
Soil organic matter (SOM) in temperate forests starts its formation on the forest floor and supports essential ecosystem functions. Understanding its composition and dynamics is crucial for sustainable forest management. SOM accumulation depends strongly on interactions with mineral compounds, which protect it from microbial decomposition through various mechanisms. Our previous research using multi-step density fractionation, chemical characterization (main cations, total carbon), and Ca-XANES spectroscopy demonstrated that bedrock type (basalt, paragneiss, dolomite, limestone) significantly influences SOM-mineral associations and binding patterns in the organic soil surface layers (Of, Oh) of beech-dominated temperate forests.
This study further examines SOM composition, focusing on functional C groups (alkyl, O-alkyl, aryl, carboxyl) of bulk soils and density fractions of organic layers from different bedrock types using Cross-polarization (CP) magic angle spinning (MAS) 13C NMR spectroscopy. We also assess biomolecular composition (carbohydrates, carbonyls, lipids, lignin, proteins, and char) through the application of the Molecular Mixing Model by Nelson & Baldock (2005) and analyze non-cellulosic polysaccharides via gas chromatography to identify primary (plant-derived) and secondary (microbial-derived) polysaccharides.
Preliminary results reveal that Of layers are primarily composed of undecomposed or partially decomposed plant-derived SOM, with light fractions (<1.6 g cm⁻³) accounting for most SOM mass, enriched in O-alkyl compounds (e.g., carbohydrates, lignin). Despite the heavy fraction (>1.6 g cm⁻³), representing mineral-associated SOM, is small in Of layers, basalt samples had the largest contribution overall. This fraction contained more proteins and lipids, indicating advanced microbial processing. The marked carbonyl/carboxyl accumulation in basalt soils suggested enhanced stabilization via carboxylate sorption to Fe and Ca mineral surfaces. In Oh layers, density fractions >1.4 g cm⁻³ dominate, reflecting increased OM stabilization and decomposition. Bedrock-specific effects include elevated lipid accumulation in paragneiss soils and higher carbonyl/carboxyl and char ̶ fire-derived OM in dolomite soils. Higher Alkyl/O-Alkyl ratios in silicate-derived soils (e.g., paragneiss) indicate advanced SOM decomposition, accompanied by increased microbial-derived polysaccharide contributions (galactose, mannose), highlighting dynamic turnover in these soils.
Our findings highlight the interplay between SOM composition, SOM-mineral interactions, and bedrock type in regulating SOM dynamics. Future Fe-XANES analysis will clarify the role of different iron species (e.g., Fe-SOM complexes, different Fe minerals) in SOM stabilization and decomposition.
How to cite: Villalba Ayala, G., Colocho Hurtarte, L. C., Klysubun, W., Katholnigg, S., and Prietzel, J.: Exploring Bedrock-Driven SOM Dynamics and SOM-Mineral Associations in Forest Soil Organic Surface Layers, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-3848, https://doi.org/10.5194/egusphere-egu25-3848, 2025.
Soil CO2 efflux is the sum of heterotrophic and autotrophic respiration. However, measuring these two fluxes separately in intact forest soils, in high spatiotemporal resolution, is challenging and costly. The apparent respiratory quotient (ARQ), defined as the ratio of CO2 efflux to O2 influx, is primarily determined by the stoichiometry of the respiratory substrate and exhibits the potential to differentiate between the components of soil CO2 efflux. Empirical studies have demonstrated that ARQ is approximately 1 for root respiration, which is associated with carbohydrate metabolism, and 0.7-0.8 for mineral soil respiration, which is associated with decomposition of soil organic matter. In order to explore the use of ARQ in respiration partitioning, we combined a novel continuous measurement of ARQ from soil chambers with laboratory incubations in a temperate pine forest. To test the ability of ARQ to partition soil respiration sources, three different approaches were applied: Firstly, root abundance was controlled by placing chambers along a root density gradient (close and far from tree stems) and by no-root control chambers. Secondly, chamber ARQ was compared with ARQ of the individual soil components. Thirdly, the results were compared to respiration partitioning evaluated by radiocarbon (Δ14C) measurements. ARQ of individual soil components was highest in roots (0.96 ± 0.01, mean ± standard error), intermediate in litter (0.88 ± 0.03), and lowest in soils from the organic layer (0.83 ± 0.04) and mineral layer (0.83 ± 0.06). The mean ARQ in the soil chambers was 0.91 ± 0.08, and was usually within the range of the individual soil components. This suggests that root respiration contributed 62% to total respiration. Chamber ARQ was higher than the no-roots chambers (0.74 ± 0.05) and higher at closer to the tree stems (0.96 ± 0.07 vs. 0.84 ± 0.09 far from the stems), suggesting that root respiration percentage from total respiration was 72% near the stems and 21% far from the stems. For comparison, according to Δ14C, root respiration’s contribution was 55% and 14% for close and far from the stems, respectively. On a diurnal timescale, soil CO2 efflux was synchronized with air temperature, while ARQ exhibited an out-of-phase relationship with air temperature, with higher values recorded during the night than daytime (0.97 ± 0.06 vs. 0.85 ± 0.10, respectively). The elevated nocturnal ARQ may be attributed to greater temperature sensitivity in mineral soil respiration than in root respiration, reduced ARQ during daylight hours due to transport of root-respired CO2 in the xylem stream, or increased root oxidation with elevated ARQ during night. Overall, our primary results indicated that ARQ is a cost-effective approach to disentangle respiratory sources at seasonal and diurnal scales.
How to cite: Zhang, Q., Trumbore, S., Lengert, A., Schäfer, T., and Hilman, B.: Pairwise O2 and CO2 in soil studies: using the apparent respiration quotient to partition soil respiration components, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-13645, https://doi.org/10.5194/egusphere-egu25-13645, 2025.
The forest floor (FF) possesses significant water retention capacity, facilitating the transfer of water between the atmosphere and the soil. However, knowledge on the water retention characteristics and water transport effects of the FF remains limited. Due to the predominance of laboratory investigations regarding the storage capacity of a forest’s litter layer, we designed and constructed a new grid lysimeter to directly and in-situ measure the water fluxes from and into the FF. The objective was to ascertain further information regarding storage capacities, retention durations, and resulting infiltration patterns.
We present the results of a network comprising forest floor lysimeters and soil moisture probes at three sites with different altitudes located in the Black Forest, SW Germany. The three sites exhibit an annual mean temperature gradient from 6.3°C to 10.3 °C, leading to humus forms that vary from typical F-Mull to typical Moder according to KA6. We analyze water fluxes in relation to two distinct tree species (beech and spruce) and varying positions under the tree crown (middle and edge).
Throughout the monitored period in 2024, we determined that water was retained up to six days in the FF, while the amount of stored water was higher in Moder compared to the F-Mull. Our innovative gridded lysimeter design enabled us to demonstrate the small-scale (0.0625 m²) variety of spatio-temporal infiltration patterns, which is significantly influenced by the FF. The findings of our lysimeter network provide a comprehensive understanding of the influence of the forest floor on the water cycle within forest ecosystems.
How to cite: Paulsen, H. and Weiler, M.: Storage and redistribution of water in the forest floor influence evaporation, retention and infiltration patterns, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-3185, https://doi.org/10.5194/egusphere-egu25-3185, 2025.
The forest floor (FF) is the central place in forests where organic matter, nutrients, and water are stored, transformed, and transferred. The rate of these processes is influenced, among other factors, by the soil temperature regime. FF horizons, lying directly within the sphere of atmospheric influence, are frequently exposed to temperature fluctuations. To understand how heat is transported through the forest floor, values for heat conductivity and heat capacity are essential. We measured these parameters in various FF horizons from temperate beech forests under controlled laboratory conditions. Thermal conductivity was measured using a single-probe needle sensor, while water content dependence was assessed through an evaporation experiment with continuous measurements. Heat capacity was measured using a dual-probe needle sensor at various stages during the evaporation period. Our results show that volumetric water content is the most significant factor influencing both heat conductivity and heat capacity. We demonstrate that, at constant water content, increasing decomposition levels in FF horizons lead to higher thermal conductivity. We also found significantly lower thermal conductivities in FF horizons compared to underlying mineral soils at similar volumetric water contents. Moreover, unlike in mineral soil horizons, higher dry densities of FF material result in lower thermal conductivity when volumetric water content and the degree of decomposition remain constant. Our results support the hypothesis of an insulating effect of FF layers, which mitigates the impacts of temperature extremes on the underlying mineral soil. We recommend incorporating the thermal conductivity–water content relationships into heat balance modeling of forest soils.
How to cite: Neumann, R., Schwärzel, K., and Trinks, S.: Thermal Conductivity of Forest Floor from Temperate Beech Forests: Laboratory Measurements and In Situ Projections, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-5470, https://doi.org/10.5194/egusphere-egu25-5470, 2025.
Soils are both significant carbon reservoirs and sources of carbon emissions, playing a critical role in the global carbon cycle. In addition to CO2 emissions from soil respiration, volatile organic compounds (VOCs) significantly influence atmospheric chemistry, ecosystem processes, and climate feedback mechanisms. While biogenic VOCs (BVOCs) from plants are well-studied, the contribution of soil-emitted VOCs remains relatively underexplored, particularly their distribution and dynamics across soil depths in forest ecosystems. This study aimed to quantify depth-specific soil VOC storage and emissions, investigate their relationship with CO2 emissions as an indicator of microbial activity, and assess how litter characteristics influence these dynamics.
The research was conducted in two forest plots at the ECOSENSE site located in the Black Forest, Germany. The plots were dominated by Douglas fir (coniferous) and European beech (broadleaf) trees. We examined VOC storage and emissions across soil depths, compared their proportions to CO2 emissions, and assessed how microbial activity and litter properties shaped these soil VOC dynamics.
Our findings reveal that VOC storage and emissions varied significantly with soil depth and litter characteristics. More specifically, VOC storage and emissions were much higher in the Douglas fir plot than those in the European beech plot, highlighting the influence of tree species-specific chemical inputs. This foundational understanding of soil VOC dynamics provides critical insights into their potential role in climate feedback mechanisms and supports future efforts to model VOC fluxes under changing environmental conditions.
How to cite: Lee, H., Kreuzwieser, J., Katlewski, S., Weber, P. C., and Werner, C.: Soil VOC Storage and Emissions Across Horizons in Douglas Fir and European Beech Forests, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-8016, https://doi.org/10.5194/egusphere-egu25-8016, 2025.
Boreal forests play a crucial role in emitting biogenic volatile organic compounds (BVOCs), which have both warming and cooling effects on the Earth's climate. These forests are among the primary sources of secondary organic aerosols (SOAs). Plant-emitted BVOCs, such as isoprenoids (including isoprene, monoterpenes, and sesquiterpenes), serve as precursors to SOAs, significantly affecting air quality and climate. Recent research indicates that forest fires also have long-term impacts on BVOC emissions, which are influenced by the frequency and severity of these fires, exacerbated by climate warming. Despite their importance, the effects of forest fires on BVOC emissions, their production and consumption by plants and associated soil microbes, as well as the underlying genetic mechanisms, remain poorly understood.
In this study, we quantify post-fire BVOC emissions from the forest floor, including above-ground plantlets, below-ground plant parts, and soil microbes by trapping forest floor BVOCs using a dynamic headspace technique. To investigate belowground BVOCs, we established mesocosms—blocks of soil with intact vegetation on top—within strictly controlled climate chambers. BVOCs were collected from mesocosm soil, as well as from root-free soil, using a dynamic enclosure technique. Soil DNA was extracted for amplification of 16S rRNA and ITS region from the samples and sent for sequencing to detect changes in microbial composition between pre- and post-fire conditions. We designed BVOC-specific probes for targeted metagenomics, such as those for monoterpene synthesis, isoprene synthesis, and monoterpene degrading enzymes, to analyze the production and consumption of BVOCs by the soil microbiome and to correlate these findings with forest floor BVOC flux data.
We have identified various volatile chemical groups, such as monoterpenes and isoprene, and quantified their fluxes in forest floor vegetation before and after fires. This study provides a clearer understanding of BVOC emissions and their consumption in the atmosphere from the boreal forest floor and soil microbiome under pre- and post-fire conditions.
How to cite: Maiti, S., Zhang-Turpeinen, H., Paul, D., Zhu, X., Sorrentino, F., Siljanen, H. M. P., Blande, J., Pumpanen, J., and Berninger, F.: BVOC fluxes in boreal forest floor and associated soil microbiome after forest fire, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-15603, https://doi.org/10.5194/egusphere-egu25-15603, 2025.
The forest floor (FF) is the central hub in forests where organic matter, nutrients, and water are stored, transformed, and transferred. The FF is dominated by plant litter and its decomposition products, and thus differs fundamentally from the mineral soil. Although the FF is the most dynamic compartment of forest soils, it is often neglected, and inconsistent terminology complicates the synthesis of information from existing studies. The FF is expected to be the most responsive to changing climate, management, eutrophication, and acidification. Here, we (1) compile existing knowledge on the role of FFs for ecosystem service provision, (2) assess the vulnerability of FFs to forest change, and (3) identify important knowledge gaps for temperate forests. The role of FFs in nutrient, carbon, and water cycles depends on the turnover rates and accumulated mass of the FF, which reflects strong interdependences with the abundance, activity and composition of soil microbial and faunal communities. These mutually reinforcing interactions determine how much the FF or mineral soil dominates biogeochemical cycles and energy fluxes. With slow FF turnover, large proportions of nutrients are tightly cycled within the FF, organic matter accumulates due to limited decomposition and impaired bioturbation, and water is channelled through preferential flow-paths. With rapid FF turnover, the mineral soil is the main place for plant nutrient uptake and organic matter transformation, and water percolates more homogeneously. Under forest change in particular ecosystems with slow FF turnover could turn from carbon sinks into sources, losing their adaptability to nutrient-poor conditions and a large part of their water storage capacity. We conclude, that combined analyses of the key organisms and feedbacks with decomposing FF litter are required to understand the resilience of temperate forests against future changes.
How to cite: Niederberger, J. and the DFG Research Group Forest Floor (FOR 5315): Temperate forest floors: Ecosystem hub in transition?, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-11387, https://doi.org/10.5194/egusphere-egu25-11387, 2025.
Mosses are abundant components of understory vegetation in coniferous forests. The poikilohydric life style of bryophytes implies that active phases in moist state alternate with inactive phases in dry state, which requires a range of physiological adaptations, such as the accumulation of sugars and antioxidants. Re-wetting of desiccated bryophytes during intensive summer rain events, however, may cause considerable leakage of intracellular moss metabolites, leading to a flush of labile carbon (C) compounds washed into the soil.
In the presented study we investigated (1) what amounts of C and nutrients are leached from forest floor mosses over a growing season; (2) how C leaching from mosses is related to the climatic conditions at the field site; (3) how moss layers alter the chemical composition of the canopy throughfall. We collected leachates under four species of forest floor mosses in two montane spruce forests differing in climate over a 4-months growing season.
Our results showed that total fluxes of dissolved organic C (DOC) by the moss leachates were comparable at the two field sites, irrespective of climatic conditions, although C concentrations were higher in moss leachates at the drier site. Surprisingly, C leaching from mosses was rather stable compared to the significant temporal variation in DOC concentration in canopy throughfall. Furthermore, we found that moss layers significantly altered the chemical quality and elemental composition of the canopy throughfall, and that this effect depended on the moss species, field site and season.
Our study demonstrates that moss leachates represent a significant soil C input and relevant labile C source for soil microorganisms besides root exudates and litter leachates, and that forest floor mosses play an important role in elemental cycling of montane spruce forests.
How to cite: Koranda, M., Risse, S., Zechmeister, H., and Wanek, W.: Effects of forest floor mosses on elemental cycling in spruce forests, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-12638, https://doi.org/10.5194/egusphere-egu25-12638, 2025.
Fire has the immediate effect that roughly half of carbon and nitrogen is emitted and lost from forest floors, that the remaining ashes fertilize the ground and pools of dead organic matter and stable black carbon is produced. Depending on the intensity of the fire it will potentially have long lasting physical, chemical and biological effects. Fire as a disturbance agent to the forest floor has acted on the forest landscapes in Scandinavia since the last glaciation as a natural phenomenon and as a result of human activities. Fires have likely occurred in all forests in Norway even though sampling and dating of charcoal in selected landscapes indicate a lower frequency along the west coast than in the southeastern forest region and in neighboring Sweden.
Where the availability of synthetic fertilizers in agriculture (ca. 1900) and the significance of timber value and -trade (ca. 1700) mark important shifts in fire occurrence and avoidance, forest fires have been successfully suppressed with documented effects since the 1970’s likely leading to an accumulation of forest floor organic matter.
Using a one-time survey of >8000 registrations of the thickness of the forest floor, its sub-layers, humus form and the occurrence of charcoal in upland forests of the Norwegian National Forest Inventory, we investigate the regional distribution of charcoal occurrence in upland forests indicating earlier fire activity and look for legacies on carbon stocks or forest floor characteristics using available national soil survey data. Forest floors in boreal and cold temperate forests hold 30-60% of total forest soil carbon stocks equivalent in magnitude to that held by the living biomass of trees. Thus, we further estimate the areas and forest floor carbon stocks most likely to gain increased vulnerability to fire under future climate conditions.
How to cite: Dalsgaard, L., Bright, R., Callesen, I., Eisner, S., and Tau Strand, L.: Forest floor charcoal and fire – extent and legacy in Norwegian forests, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-12430, https://doi.org/10.5194/egusphere-egu25-12430, 2025.
Biological N2 fixation is a major nitrogen (N) source in boreal forests, but the factors controlling N2 fixation in boreal forests are not well understood. Most plants in boreal forests rely on mycorrhizal fungi to take up N, boreal forest soils are typically acidic, and the high abundance of mycorrhizal fungi and low soil pH could restrict the abundance of diazotrophs and N2 fixation. To investigate the effects of mycorrhizal fungi and soil pH on N2 fixation two experiments were conducted over several years in a mature Pinus sylvestris forest in the boreal zone of Sweden; a pine and shrub root exclusion experiment and a liming experiment. We measured non-symbiotic N2 fixation, soil carbon (C) and nutrient availability, and the quality of soil organic matter over one growing season, eight and 40 years after the root trenching and liming experiments started, respectively. Both experiments showed that N2 fixation was still very low in June (during a 48 h incubation at 15°C), indicating that diazotrophs are dormant during large parts of the years and only regain their activity slowly. Further, we found that exclusion of pine roots and associated ectomycorrhizal fungi significantly increased the rate of non-symbiotic N2 fixation in the late growing season, while exclusion of shrubs and associated ericoid mycorrhizal fungi showed no significant effect. Exclusion of pine roots, shrubs and the associated mycorrhiza strongly increased soil NH4+-N concentrations and the aromaticity of the water-extractable organic matter but did not significantly affect non-symbiotic N2 fixation. The reason for this might be that the low soil C quality and the high soil N availability offset the effects of the reduced abundance of mycorrhizal fungi on N2 fixation. In contrast to our expectation, liming did not significantly increase the rate of N2 fixation, suggesting that soil pH was not the key factor limiting N2 fixation. Overall, this study suggests that the diazotrophs are in a dormant state during most part of the year. Further, the results indicate that tree roots and ectomycorrhizal fungi rather than shrubs and ericoid mycorrhizal fungi or acidic conditions restrict non-symbiotic N2 fixation in boreal forests.
How to cite: Xu, W., Clemmensen, K. E., and Spohn, M.: Long-term effects of root removal and liming on non-symbiotic N2 fixation in boreal forests , EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-5414, https://doi.org/10.5194/egusphere-egu25-5414, 2025.
Riverine systems are distinct components of the natural environment which have significant roles in storing and processing terrestrial carbon. While processing organic matter, rivers release large amount of greenhouse gasses to the atmosphere. In this light, headwater streams are particularly interesting. Due to their high connectivity with the surrounding landscapes, these small streams are strongly influenced by terrestrial inputs of carbon and nitrogen and groundwater inflow. Therefore, despite smaller surface area, their role in C and N cycling is crucial. The amount and character of C and N inputs to headwater streams is highly dependent on soil and vegetation types of the catchment. Soils, connecting the atmosphere, hydrosphere and lithosphere and supporting various ecosystem processes, are believed to exhibit strong responses to ecosystem disturbances. Among these disturbances are climate change impacts and modified landcover.
The aim of this study is to analyze three-dimensional variability of biogeochemical processes in the soils of a forested headwater catchment, following partial clearcut of a spruce forest.
The high resolved data on soil properties were collected in the Wüstebach catchment (Eifel/Lower Rhine Valley), a long-term environmental observation site of the TERENO (Terrestrial Environmental Observatories) project. The Wüstebach is a forested catchment in which nine hectares of Norway spruce was cleared in 2013 and has been replanted with original beech.
Three extensive soil sampling campaigns were conducted in the catchment: the first just before a partial clear-cut in 2013, the second after the clearcut in 2014 and the third, five years after the clearcut in 2018. The sampling produced high-resolution data on physical and biogeochemical soil parameters per horizon.
The plan of this study is to perform geostatistical analysis of the data and produce three-dimensional surface prediction models of the spatial distribution of the two nutrients: C and N in 2013, 2014 and 2018 over the entire catchment.
How to cite: Batsatsashvili, M., Dedden, L., Bol, R., Gettel, G., Kalbitz, K., Wiekenkamp, I., and Pütz, T.: Deforestation effects on the spatial distribution of C and N in the soils of a forested headwater catchment in the Eifel, Germany, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-12987, https://doi.org/10.5194/egusphere-egu25-12987, 2025.
Leaf-litter decomposition is a key driver of carbon (C) and nutrient cycling in terrestrial ecosystems, governed by climate and the litter chemical composition. Silicon (Si), a ubiquitous element in terrestrial ecosystems that has various beneficial effects on plants, is an integral component of leaf-litter. However, the relationship between leaf-litter decomposition and Si content remains poorly constrained, particularly in temperate beech forests where Si uptake predominantly occurs through passive mechanisms. Here, we investigated the relationships between total beech-leaf Si content, mass loss, decomposition rate (k), and contents of C and nitrogen (N) of beech (Fagus sylvatica) leaf-litter under five temperate beech-forest stands with differing microclimatic conditions, in two sandstone regions of Lower Saxony, central Germany.
We incubated 441 leaf-litter bags that were sampled bi-monthly over two years to capture fine-scale temporal decomposition dynamics. Each site was equipped with soil temperature and moisture loggers, allowing differentiation of the sites into three microclimatic classes: (i) warm-dry (14.5°C mean topsoil (0-6 cm) temperature, 21% mean soil moisture), (ii) intermediate (13.2°C, 31.4%), (iii) cool-wet (9.7 °C, 38.8%).
The median total Si content of beech leaves across all sites was 1.1% dw-1, comparable to the 1.0% dw-1 observed in unincubated leaf-litter samples. Decomposition rate (k) was positively related to Si content under intermediate (R2 = 0.14, p < 0.05) and warm-dry (R2 = 0.2, p < 0.05) conditions, whereas no such relationship was observed under cool-wet conditions. Median k values were noticeably higher under both cool-wet and intermediate conditions (0.31 g yr-1) compared to warm-dry conditions (0.18 g y-1). There was no relationship between Si and C content, but N content exhibited a weak but positive correlation with Si under all climate conditions, with the strongest relationship observed under warm-dry conditions (R2= 0.21, p < 0.05). Over the two-year study, C content decreased from an initial 49% to 41% under intermediate conditions, representing only 16.8% decrease, while N content increased from 0.9% to 1.42% under the same conditions. During mass loss for the same period, Si and N contents increased while C content decreased across all sites. These findings reflected immobilization of N by microbes, but a release of C with mass loss.
The stability of Si content over time, along with the positive relationship to mass loss, suggests that the total Si pool of beech leaves predominantly comprises structured opal compounds that resist mineralization under temperate forest conditions. While this has theoretical implications for linking the Si cycle to C sequestration, the weak relationship observed here, coupled with the decreased C content, suggest further investigation. We conclude that Si influences litter decomposition in a context-dependent manner, with stronger effects under drier and warmer conditions, where soil moisture limitations may intensify its role in C and nutrient cycling.
How to cite: Asabere, S. B., Drollinger, S., Mohebbi, B. B., Poudel, S., and Sauer, D.: Assessing silicon’s role in leaf-litter decomposition, carbon and nitrogen cycling across microclimates in temperate beech forests , EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-13812, https://doi.org/10.5194/egusphere-egu25-13812, 2025.
Forest ecosystems are critical hubs of biogeochemical activity, playing a major role in global carbon cycling by storing and cycling substantial quantities of terrestrial carbon both above and below ground. The forest floor serves as a dynamic interface where organic inputs, such as litterfall and root turnover, drive soil processes that influence carbon fluxes. Understanding the interactions between photosynthetic activity, soil respiration, and decomposition is key to determining whether forests act as carbon sources or sinks. To gain deeper insights into these processes, it is essential to measure soil respiration and partition its autotrophic and heterotrophic components, linking aboveground organic inputs to belowground carbon and nutrient cycling.
This study investigates soil carbon flux dynamics in three distinct Irish forest types: a commercial coniferous forest on mineral soil, a broadleaf-dominated native woodland on mineral soil, and a mixed-species forest on peat soil. These forests, characterized by differences in soil type, species composition, and management practices, offer unique insights into the interactions between litterfall, fine root dynamics, and soil respiration.
Aboveground litter inputs were quantified through monthly litterfall collection using bucket traps over a two-year period, revealing distinct patterns both within and between sites. Litter decomposition was assessed with one-year litterbag experiments, while fine root production and turnover were evaluated using one-year in-growth core experiments. Soil respiration was measured twice monthly over a two-year period using two trenched collars installed to a depth of 25 cm and two untrenched collars, with the inclusion and removal of litter enabling a detailed analysis of autotrophic and heterotrophic contributions. Elemental analysis of mineral soils (0–50 cm) and organic soils (0–150 cm) provided key insights into carbon, hydrogen, and nitrogen content, offering valuable data on soil organic matter composition and nutrient availability across the soil profile in the three forest types.
Over the two-year study period, results show that the commercial coniferous forest exhibited the lowest average total soil respiration rates, averaging 52.10 tonnes CO₂/ha/yr. Conversely, the native woodland and the mixed-species peatland forest showed similar and higher soil respiration rates, averaging 54.31 tonnes CO₂/ha/yr. Across all sites and seasons, heterotrophic respiration contributed more to total ecosystem respiration than autotrophic respiration.
By integrating data on litterfall, decomposition, fine root dynamics, and soil elemental composition, this study highlights the critical role of organic inputs and root processes in driving soil respiration and carbon cycling in forests. These findings will enhance carbon modeling efforts, improve predictions of ecosystem responses to environmental change, and inform sustainable forest management strategies for climate change mitigation.
How to cite: Ruffing, B., Tobin, B., Saunders, M., and Byrne, K.: From Litterfall to Respiration: Investigating Soil Processes in Differing Irish Forests, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-13934, https://doi.org/10.5194/egusphere-egu25-13934, 2025.
Previous research show that soil fauna can consume about how of annual litter fall across world biomes. In some ecosystems such as temperate broadleaf forest it can be almost all annual litterfall. In this study we use simple field microcosm experiment quantify amount of carbon incorporated by so fauna bioturbation in various forest ecosystems. We have found that more than half of carbon eaten by soil fauna, gets incorporated in the soil by fauna bioturbation. Soil fauna biotubation increased which increasing actual evapotranspiration and decreasing CN ratio of litter.
By comparing manipulation experiment, proportion of biostructures in soil measured by thin soil sections, and carbon distribution in top soil layers, in ecosystem which different abundance of soil fauna causing bioturbation, namely earthworms, we can demonstrate, that soil fauna bioturbation is a major process responsible for distribution of organic matter in litter overlaying soil horizons and mineral soil. This indirectly affect fungal bacterial ration, composition of soil food web an many other soil processes
How to cite: Bartuška, M. and Frouz, J.: Soil fauna as a webmasters of forest floor, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-6585, https://doi.org/10.5194/egusphere-egu25-6585, 2025.
The mycorrhizal symbiosis is a central component of plant-soil feedbacks and carbon (C) cycles of forest ecosystems. Yet even though it is known that the two major mycorrhizal association types influence litter decomposition and soil organic matter formation differently, it remains unresolved whether this also influences their preference for the forest floor as a habitat. We aimed to test such preference in mature European beech (Fagus sylvatica L., ECM host) forests admixed with sycamore maple (Acer pseudoplatanus L., AM host) by measuring extracellular enzyme activities in the forest floor and mineral soil of twelve study sites located across gradients of rising temperature and inorganic phosphorus (P) limitation. Sampling took place in the forest floor and at 0-5 cm, 5-10 cm and 10-20 cm soil depth in the proximity of beech and maple trees, respectively, and the activity of recalcitrant C and organic P and nitrogen (N) degrading enzymes were analyzed. In our presentation we will discuss whether our results support the hypotheses that (i) mycorrhizal fungi are more dependent on forest floor C in nutrient-poor forest stands and (ii) arbuscular mycorrhizal fungi are superior in P-poor forest floors and ectomycorrhizal fungi in P-rich forest floors.
How to cite: Meier, I. C., Bergmann, M., Buske, B., Dietz, F., Bidartondo, M., and Martinez-Suz, L.: The forest floor as a habitat for mycorrhizae across temperature and P availability gradients, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-17399, https://doi.org/10.5194/egusphere-egu25-17399, 2025.
Temperate production forests have experienced a homogenization of forest structure under established management regimes, leading to a loss of biodiversity and changes in ecosystem functions, as well as a decreased resilience to disturbances. Management approaches such as the Enhancement of Structural Beta Complexity (ESBC) aim at reintroducing heterogeneity in production forests by emulating natural disturbances and succession through silvicultural manipulations. By breaking down organic matter and making it available for other organisms, decomposition processes and their associated invertebrate communities are an integral part of nutrient and carbon cycling. Animal derived necromass, such as carcasses and dung, is especially nutrient rich and provides due to its ephemeral nature resources for specialized decomposer communities. Through their tunnelling behaviour common dung beetle and burying beetle species, such as Anoplotrupes stercorosus and Nicrophorus vespilloides, play an important role in forest soil functioning by improving aeration and increasing nutrient input into the soil. Controlled by factors such as microclimate, which are directly influenced by forest stand structure, these processes and communities are likely strongly affected by forest stand homogenisation.
As part of the BETA-FOR research unit this study aims at disentangling the relationship between homogenization and decomposition in temperate production forests with a focus on decomposition rates and decomposer diversity. We have introduced different ESBC treatments by creating deadwood and canopy openings at eleven forests sites in production forests in Germany, each site comprised of nine ESBC-plots and nine control-plots (closed forests). On each plot, decomposition rates of different necromass, such as animal dung and rat carcasses, were determined by exposing the materials to plot conditions for specific lengths of time in spring and in summer 2023. Pitfall traps baited with dung and carcasses were installed directly afterwards to investigate decomposer diversity.
We found no difference in gamma- and beta-diversity of dung beetles and necrophagous beetles between ESBC-forests and control forests. However, Dung removal rates and dung beetle biomass decreased with increasing temperature. Dung beetle abundance and biomass, as well as dung removal rates were lower in summer and in warmer regions, this effect was especially strong on those plots of the ESBC-forests that had open forest canopies. Additionally, alpha diversity of both dung beetles and necrophagous beetles was lower on plots with open forest canopies in all regions.
This demonstrates that some important forest communities might not benefit from increased structural heterogeneity in forest stands and even react negatively to some aspects, such as more openings in the forest canopy. Canopy openings, especially in combination with higher temperatures, negatively impacted dung beetle communities, showing that under future climate warming and changes in forest structure these communities might face increased pressures.
How to cite: Asch, J., K. Peters, M., and Scherer-Lorenzen, M.: Effects of forest structure and climate on decomposition processes and decomposer communities , EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-20671, https://doi.org/10.5194/egusphere-egu25-20671, 2025.
The forest floor (FF) represents the interface between the production of aboveground biomass and the belowground cycling and storing of C. The conditions within the FF, including its structure, faunal community composition, and microbial activity, may influence the pathway, quantity, and stability of organic matter (OM) transferred and stored in the mineral soil beneath. C inputs like litter are either mineralized to CO2, leached as dissolved organic C (DOC) into deeper soil, transformed into stable soil organic matter (SOM) by microbial communities or transferred into the mineral soil through soil fauna. While the impact of certain macrofauna like earthworms is well-studied, the role of mesofauna remains less understood despite evidence of their contribution to SOM cycling. To address this the DFG research group “Forest Floor” established a field mesocosm experiment across elevation gradients within temperate mixed forests in Germany and Switzerland. Four gradients were set up across different types of parent material including basalt, paragneiss, and limestone, resulting in differing FF types across and within gradients. Within each site, mesocosms were installed under beech- and maple-dominated canopies, respectively. The mesocosms had vertical openings on the sites covered with different mesh sizes (4 mm, 1 mm, and 0.045 mm) to allow horizontal movement in and out of the mesocosm. These mesh sizes create three size compartmentalized soil fauna communities with increasing limitations due to body size. A set of mesocosms with 4 mm mesh size is non-rotated while all other mesocosms are regularly rotated to limit root ingrowth. Site-specific FF was placed into the mesocosm undisturbed, then defaunated and its Ol horizon was replaced with beech or maple litter highly enriched with 13C, 15N, and 2H. We measure CO2 and 13CO2 1 ,2 ,4 ,6 ,12, and 16 months after the mesocosm were placed in the field. DOC is collected bi-weekly in suction plates below the non-rotated mesocosms. This will allow us to establish a mass balance of beech and maple litter turnover as affected by different soil fauna communities in contrasting FF types. We expect the FF to accumulate with decreasing mesocosm accessibility resulting in a shift in C fluxes. A lower CO2 flux due to unfavorable conditions might be counterbalanced by increased DOC production.
How to cite: de Jong, P., Chen, J., Schleppi, P., Doetterl, S., Scheu, S., and Hagedorn, F.: How soil fauna affects carbon fluxes in forest floors: Insights from size compartmentalized communities, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-18261, https://doi.org/10.5194/egusphere-egu25-18261, 2025.
Slow turnover of the forest floor (FF) is often assumed to be related to immobilization of nutrients within the organic matter. However, the FF is also assumed to be an important nutrient source at sites with low nutrient concentrations in the mineral soil. Yet, little is known about the availability of nutrients present in the FF and how it is related to FF turnover.
Within the DFG-funded Research Unit FOREST FLOOR we identify processes that control the relevance of the FF for tree phosphorus (P) nutrition as compared to the mineral topsoil in European beech (Fagus sylvatica) forests with admixtures of spruce (Picea abies) and maple (Acer pseudoplatanus). We quantified plant-available P at lab conditions using resin exchangers in the FF and the mineral topsoil up to 20 cm along four elevation-related temperature gradients of different soil P status. We hypothesize that the FF gains in importance for P nutrition with decreasing P status of the mineral soil.
Results show that along the P gradient with high mean annual temperature (MAT: 9-10 °C), highest resin extractable P (Presin) concentrations within one site are found in the mineral soil. On the P gradient with low MAT (5-6.1 °C) however, highest Presin concentrations are found in the FF and also in SOM rich mineral soil, especially at the silicate site with low total P concentrations. This translates into surprisingly high Presin values under beech (P-poor site Kandel, Black forest FF: 290 ± 200 µg P/g soil, Ah horizon: 410 ± 110 µg P/g soil), which corresponds to twice the amount extracted by citric acid. Presin concentration under beech clearly differed from plots under spruce and maple with mostly 100 µg P/g soil at all temperature classes for P poor mineral soils. However, this high P availability in the FF was not observed for carbonate sites.
In conclusion, the innovative resin extraction method provided new insights regarding P nutrition in beech forests compared to citric acid as reference method. High P availability under beech at Kandel despite low MAT and low P status of the mineral soil indicate a tight recycling of P resources via the FF and SOM rich mineral soil. Our results show that the effect of increasing MAT on P availability depends on the P status of the mineral soil. These findings suggest a crucial role of the FF for beech forest P nutrition and its potential vulnerability under climate change.
How to cite: Schilling, L., Vesterdal, L., Prietzel, J., and Lang, F.: Resin extractions from forest floors reveal tree specific adaptation to the phosphorus status of the mineral soil in European beech forests, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-18496, https://doi.org/10.5194/egusphere-egu25-18496, 2025.
In-situ imaging of iron and manganese mobilisation in forest floor layers
Mobility of iron and manganese in forest soils is controlled by the redox state, the overall pH-value and the concentration of complexing organic acids. The solubility of Mn and Fe oxides is an indicator of reductive activity processes and furthermore strongly connected to the availability of phosphorus for plants. Yet the strong small-scale heterogeneity of forest floor makes the spatial and temporal patterns of stable and soluble iron and manganese forms challenging to quantify. 20 etched 10x15cm glass slabs were coated with either an iron or manganese oxide (goethite and birnessite, respectively). Slabs were vertically inserted in the forest floor with close contact between the oxide coating and the soil, and left for one growing season in a spruce-beech forest. The forest floor was a moder circa 12 cm thick, and the soil was a Dystric Cambisol. In fine humus-rich Ohf and Obh horizons, the rate of mobilisation of goethite and birnessite was generally > 50 % of the area, with more birnessite lost than goethite. Most mobilisation was found along the finest roots in the organic horizons. For goethite, mobilisation underwent a gradual transition from high mobility in organic horizons to minimal mobility in mineral soil. For birnessite in contrast, there was barely any mobilisation in mineral soil. The substantial mobilisation in organic horizons primarily along fine roots suggest that complexation by exuded organic acids is a dominant process in iron and manganese mobilisation. Yet deeper in the forest floor and mineral soil, reductive processes due to aeration deficiencies likely play the major role in iron and manganese mobility. Since the complexation of iron by organic acids can enhance phosphorus availability, we conclude that the spatial pattern of iron mobilisation reflects the root- and mycorrhiza-driven P-mobilisation.
How to cite: Hahn, J., Lang, P. Dr. F., and Schack-Kirchner, P. Dr. H.: In-situ imaging of iron and manganese mobilisation in forest floor layers, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-18998, https://doi.org/10.5194/egusphere-egu25-18998, 2025.
Large-scale (i.e., > 1ha) clearcuts were studied in 2022–2024 at fifteen sites across the Czech Republic. Chemical properties and stock of selected elements were assessed in organic topsoil (OF+OH) and mineral soil (0–30 cm) layers in a block design on salvage-logged plots with different management of logging residues (cleaning vs. chipping) and adjacent control (survived) stands of Norway spruce (Picea abies L. Karst.). The rate of organic matter (OM) decomposition at the logged and control plots was evaluated based on the decomposition the experiments with standardized teabags and litterbags using the in-situ organic material (organic topsoil layer).
Changes in the water-extractable organic carbon (DOC) contents showed accelerated mineralization of organic matter on clearcuts. Significant differences in the quality of organic matter between the clearcut and a control stand were found only in the organic topsoil. No significant differences were found in the soil contents of risk elements (aqua-regia extracted As, Cd, Cu, Pb and Zn) between the clearcuts and a control treatment. Moreover, the distributions of risk elements in the soil profiles did not differ depending on the management of logging residues. Evaluation of the OM decomposition indicates slightly different weight loss of the samples from the stands and from the clearcuts, depending on the management of logging residues and the chemical composition of the organic layer.
This research was funded by the Ministry of Agriculture of the Czech Republic, project No. QK22020217.
How to cite: Novotný, R., Tejnecký, V., Valtera, M., Pavlů, L., Fadrhonsová, V., Holík, L., Borůvka, L., and Šrámek, V.: Changes in organic matter and upper mineral soil on clear cuts, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-20166, https://doi.org/10.5194/egusphere-egu25-20166, 2025.
Posters virtual: Tue, 29 Apr, 14:00–15:45 | vPoster spot 3
EGU25-20206 | ECS | Posters virtual | VPS14
Upscaling forest floor properties: identifying drivers and assessing temporal changes on a regional scaleTue, 29 Apr, 14:00–15:45 (CEST) | vP3.7
Forest floor (FF) properties, such as thickness, mass and morphology, are critical indicators of forest ecosystem dynamics, shaped by climatic conditions, nutrient deposition and tree species composition. Despite their ecological importance, systematic assessments of the drivers and temporal changes in FF properties across spatial scales remain limited. This knowledge gap hinders the ability to extrapolate site-specific findings to broader regions, crucial for understanding and managing forests under changing environmental conditions.
We focus on identifying the drivers of FF properties and examining how these properties have changed over time at local and regional scales. Using data from inventories, such as the NFI (National Forest Inventory) 3 & 4 and the NFSI (National Forest Soil Inventory) 2 & 3, we investigate relationships between FF properties and key environmental factors, including climate variables, nutrient availability and forest management. This will involve examining spatial patterns and temporal trends in FF properties and understanding how drivers such as climate, nitrogen deposition and shifts in tree species composition influence these patterns. By leveraging statistical and geospatial modeling approaches, the project aims to refine methods for transferring plot-level data to broader scales, ensuring reliable representation of FF variability and trends. The inventory-based results on the factors influencing FF are compared with the process-oriented investigations at the study sites of the Forest Floor project (DFG FOR 5315) in order to be able to interpret the correlations found in the inventory data.
The outcomes of this research will provide crucial insights into how FF properties respond to environmental and management changes, contributing to improved forest monitoring and sustainable management strategies. By bridging the gap between localized observations and large-scale assessments, this work supports national and international efforts to evaluate FF in the context of climate change and other impacts.
How to cite: Rubin, L., Jost, P., and Puhlmann, H.: Upscaling forest floor properties: identifying drivers and assessing temporal changes on a regional scale, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-20206, https://doi.org/10.5194/egusphere-egu25-20206, 2025.
