Tropical ecosystems are threatened by escalating anthropogenic activities that worsen global change, potentially disrupting the carbon (C) equilibrium in tropical forests and affecting global climate regulation. While considerable research has explored the impact of global change on aboveground tropical vegetation, our comprehension of belowground components, particularly roots that mediate plant-soil interactions, such as nutrient and water uptake, remains limited. We conducted an analysis of existing research on how tropical roots respond to key global change drivers, including warming, drought, flooding, cyclones, nitrogen (N) deposition, elevated (e) CO₂, and fires. Drawing from tree species- and community-level outcomes from experimental studies, we compiled 266 root trait observations from 96 studies conducted across 24 tropical countries. From the existing knowledge, we noted in this review that tropical root systems tend to increase in biomass in response to warming and eCO₂, but community-level experiments were rare for warming and non-existent for eCO₂. Drought increased root:shoot ratio without changing root biomass, indicating a reduction in aboveground biomass. While N deposition may not greatly impact most tropical forests in the short term due to strong phosphorus limitation, mycorrhizal colonization and root phosphatase exudation were predominantly down- and up-regulated, respectively. Cyclones, fires, and flooding resulted in decreased root biomass, which, under elevated CO₂ and warming, could lead to greater carbon losses from tropical soils. Cyclones and fires increased root production, potentially in response to plant community shifts and nutrient input, while flooding altered compounds related to plant regulatory metabolism due to low oxygen conditions. We also emphasize the importance of in situ studies, comparing adapted versus non-adapted species to these disturbances and the need for methodological consistency among experiments. Our findings underscore the necessity for further research to enhance our understanding of tropical root responses to global changes. The responses of root traits and dynamics to several global change drivers would affect the functioning of the whole forest and, consequently, carbon cycling and stocks above and belowground.

How to cite: Lugli, L. F. and Yaffar, D. and the TropiRoots Network - Tropical Root Trait Initiative: The impacts of several global change drivers on tropical root traits and dynamics, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-9347, https://doi.org/10.5194/egusphere-egu24-9347, 2024.

Designing plant mixtures with potential to increase soil organic carbon (SOC) appears to be a powerful nature-based tool to restore some of the carbon lost in agroecosystems. However, we are uncertain about the best way to design such benign plant mixtures. Trait-based approaches are increasingly used to explain the relationship between plant diversity and ecosystem functions, offering a conceptual opportunity to address this knowledge gap. In this study, we combine a global meta-analysis of 407 paired SOC content observations with a root traits database from GRooT, to explore the optimum way for the design of plant mixtures to increase SOC. We found that specific root traits at the community level were important predictors of the response of SOC to plant mixtures. Species mixtures could increase SOC content when the overall plant community had low variation in root mycorrhizal colonization and root tissue density. The positive response of SOC content to species mixtures was linked to increases in soil microbial biomass carbon and root biomass. Additionally, the SOC enhancements by plant mixtures were often found in regions with high precipitation and low sand content. Our meta-analysis presents a framework based on plant traits to enhance SOC sequestration using plant mixtures, which will enable farmers to optimize plant mixtures towards soil carbon sequestration.

How to cite: Yin, S., Chen, X., Terrer, C., Zhou, Z., Chen, J., and Abalos, D.: Increasing root trait complementarity in species mixtures may be detrimental for soil carbon storage, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-12367, https://doi.org/10.5194/egusphere-egu24-12367, 2024.

Climate change mitigation and adaptation is a major challenge of modern agriculture. Increasing the incorporation of atmospheric carbon (C) as organic matter into soils through improved crop management seems to be a promising agricultural management option for supporting climate change mitigation. In order to build up soil organic C increased organic C inputs to the soil are urgently needed. In agricultural soils, crop roots are the major source of C inputs and pivotal for long-term C storage compared to aboveground biomass as their turnover is 2 to 3 times slower. This suggests, that variety selection towards increased root biomass can enhance root C inputs to the soil and could therefore increase C stocks and potentially facilitate C sequestration in soils. To quantify whether biomass allocation is affected by variety x environment interaction, we assessed root biomass, root distribution to 1 m soil depth and root: shoot ratios in a set of 10 different varieties grown at 11 experimental sites, covering a large European climatic gradient from Spain to Norway.

Preliminary results show a broad variety-specific variation in biomass production and its allocation between roots and shoots. Root biomass ranged from 1 to 3.5 Mg ha^-1 in the best variety and could be increased by 20% by selecting the best variety compared to the average root biomass without compromising yield. Root to shoot ratios varied between 0.04 and 0.58 with a mean of 0.16. Increased root biomass due to deeper roots may stabilise yields under future climate change conditions where increased frequency of drought events during vegetation periods are expected and may therefore be a climate change adaptation measure that increases the crops resilience towards changing environmental conditions. Thus, improved variety selection can help to achieve both goals of modern agriculture: climate change mitigation and adaptation.

How to cite: Heinemann, H., Seidel, F., Don, A., and Hirte, J.: Increasing root-derived soil carbon input to agricultural soils by variety selection of winter wheat, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-7528, https://doi.org/10.5194/egusphere-egu24-7528, 2024.

The enhancement of biodiversity's positive impact on ecosystem functioning (BEF) over time is commonly observed and attributed to the accumulation of mutualists and dilution of antagonists in more diverse communities. If antagonists play a role in the BEF relationship, the reduction of plant antagonists in more diverse communities, could allow plants to reduce allocation to defence. This study aimed to assess the influence of plant diversity on the expression of defence traits in 16 plant species. Our hypotheses were: (1) increased plant diversity reduces allocation to defence, (2) this reduction is more pronounced in roots than in leaves, and (3) this effect varies among species.

We measured both physical and chemical defence traits in leaves and fine roots across communities with varying plant species richness in a 19-year-old biodiversity experiment. Using established methods and an innovative metabolome approach, we explored the interactive effects of plant diversity and species identity on defence traits through linear mixed models.

Our findings were mixed concerning the first hypothesis, with only some leaf defence traits (leaf mass per area, leaf dry matter content, and hair length) showing reduction along the diversity gradient. Unexpectedly, the values of some root traits, root tissue density and nitrogen content, suggested increased allocation to defence along the same gradient. This might be attributed to these traits serving other functions, e.g. in resource acquisition and competition, which potentially overruled the impact of declining antagonists on plant defences. Our results did not support the third hypothesis, suggesting an overall convergence responses to biotic and abiotic factors related to plant diversity after two decades.

While evidence for a consistent reduction in defence trait expression along the diversity gradient was limited, our findings underscore the complex nature of BEF relationships. Further experiments, possibly controlling confounding factors on trait expression or manipulating antagonist pressures along diversity gradients, are needed to elucidate the underlying mechanisms.

How to cite: Bassi, L.: Intra- and inter-specific changes in leaf and root defence traits along an experimental plant diversity gradient., EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-3368, https://doi.org/10.5194/egusphere-egu24-3368, 2024.

When assessing the carbon storage potential of a crop, it is useful to 1) quantify the inputs that return to the soil, such as roots, rhizodeposition and sometimes aboveground biomass, and 2) estimate the carbon gains or losses attributed to the priming effect. This allows to draw up a balance of inputs and outputs at the end of the growing season. While the quantity of carbon supplied by roots and aboveground biomass is relatively easy to measure, the quantity of rhizodeposition and the priming effect are not.

To establish such a balance, 12 intercropping plant species from 3 plant families (brassicaceae, fabaceae and poaceae) were grown for two months in mesocosms (15 liters) under controlled conditions simulating a temperate summer climate in real time in an ecotron. Multi-pulse atmospheric labeling with ¹³CO₂ 99% was used to trace photosynthesized carbon and thus quantify aboveground and root biomass, rhizodeposition and variations in carbon stock due to the priming effect.

The results show that rhizodeposition represents a significant carbon input (around a quarter of root biomass), positively correlated with root biomass. Root biomass is therefore one of the main traits to be considered for increasing inputs. At the same time, 10 out of 12 plants accelerated the mineralization of soil organic matter (positive priming effect), resulting in a cumulative carbon loss over the course of the plant's growth that can be of the same order of magnitude as the biomass input.

This priming effect is highly heterogeneous and difficult to explain by plant traits, but seems quantitatively more important for brassicaceae. We propose that this variability is due both to the spatial heterogeneity inducing these processes, but also to the great variability of processes that can occur in the rhizosphere, processes that can simultaneously lead to an acceleration and/or deceleration of the decomposition of native soil organic matter.

How to cite: Hulin, B., Chollet, S., Massol, F., and Abiven, S.: Quantification of rhizodeposition and priming effect of intermediate crops via 13CO2 labeling., EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-5143, https://doi.org/10.5194/egusphere-egu24-5143, 2024.

Plants in tropical forests are thought to allocate a substantial portion of their photosynthetically fixed carbon (C) to the rhizosphere as exudates. These exudates serve multiple functions, including the mobilization of soil nutrients such as phosphorus (P), which is crucial for plant growth. In Amazonia, the predominant soils have notably low P concentrations, and plants likely employ a variety of strategies for P acquisition. However, the role of root exudates in P-impoverished Amazonian soils has not been empirically explored so far. To fill this gap, we investigated the largely uncharted territory of root exudation, as part of the Amazon fertilization experiment (AFEX), in a mature tropical forest growing on highly-weathered P-impoverished soils of central Amazonia. Our research examined root exudation in situ, both under natural soil conditions and P addition. We assessed the concentration of total organic carbon (TOC), total nitrogen (TN), and a suite of organic acids in root exudates, as well as additional root physiological and morphological traits of relevance, to potentially explain the variability in root exudation rates.

Our study revealed higher root exudation rates of TOC and organic acids in control, compared to P-addition plots, which suggests that plant C allocation to root exudates is an adaptive response to P availability. We also found that root exudation traits align with various morphological and physiological traits within the root economic space. Our findings provide insights into the hidden dynamics of root-soil interactions and have significant implications for understanding C cycling in tropical forests, shedding light on the complex coordination of root P acquisition strategies under different soil P conditions. 

How to cite: Reichert, T., Fuchslueger, L., de Andrade, S. A. L., Bauerle, T., Borghi, A., P. Darela-Filho, J., Fleischer, K., Hafner, B., Hartley, I. P., Di Ponzio, R., A. Quesada, C., Rammig, A., Schmeisk, J., and Lugli, L. F.: Effects of soil phosphorus on root exudates in central Amazonia, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-5403, https://doi.org/10.5194/egusphere-egu24-5403, 2024.

How to cite: Amelung, W., Seidel, S., Schweitzer, K., Baumecker, M., Gocke, M., Bauke, S., and Schmittmann, O.: Subsoil management as tool for climate-change adapted agriculture, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-18166, https://doi.org/10.5194/egusphere-egu24-18166, 2024.

Subsoils can store significant amounts of water, soil organic carbon and nutrients. In consequence, agricultural subsoil management is being increasingly tested as an option to sustain crop productivity under unfavourable conditions.

The Soil3 project funded by the Federal Ministry of Education and Research of Germany aims at investigating the potential of subsoil management for agriculture. In the frame of this project, we collected samples from a field experiment taking place in Thyrow (Brandenburg, Germany), at a location with low precipitations and the soil was classified as a Retisol. The experiment was designed to investigate the potential benefits of deep ploughing together with deep placement of organic fertilizers on agricultural productivity and soil organic matter stocks. We focus on three treatments, namely the control plots, the plots after deep loosening, and the plots after deep loosening and compost incorporation.

We quantified the changes in C and N stocks and in two size fractions obtained by wet sieving (<20µm and >20µm). We also recorded hyperspectral images of 1-metre soil cores in the Vis-NIR range (400-990 nm) and modelled the C distribution at a high spatial resolution (pixel size = 53×53 μm²).

The spatial distribution of soil organic matter resulting from the incorporation of organic fertilizer in the subsoil is modelled at the sub-millimetric scale. The organic matter stocks and C:N stoichiometry are both impacted by the agricultural management and the imaging technique allows us to distinguish between increased amount of organic matter in hotspots or in soil mineral matrix, and to discuss the mechanisms controlling the observed changes.

How to cite: Guigue, J., Schweizer, K., Schmittmann, O., Baumecker, M., and Kögel-Knabner, I.: Subsoil amelioration in agriculture: Deep loosening and compost incorporation in a Retisol, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-19872, https://doi.org/10.5194/egusphere-egu24-19872, 2024.

Roots can add significant amounts of carbon (C) to the subsoil, which enhances soil fertility and can mitigate climate change. About 5% of agricultural soils in Germany have been deep-ploughed (ploughing depth 30-120 cm) at least once. This technique can provide better root access to the subsoil and may help to increase yields. Studies on deep-ploughed soils focused on C stability, whereas not much is known about root-derived C in the subsoil (>0.3 m). We hypothesized that five decades after deep-ploughing, root-derived C stocks were higher compared to conventionally ploughed treatments due to better root development. This was measured by analysing suberin and cutin monomers as tracers for root- and shoot-derived C at three former deep-ploughed sites in N Germany with different soil textures and different deep-ploughing depths. Concentrations of suberin monomers in the soil were positively correlated with root biomass, this was especially strong at one sandy site. Suberin contributed more to the bulk soil organic carbon (SOC) stocks than cutin throughout the soil profile, independently of the ploughing depth. The three sites responded differently to deep-ploughing. The contribution of suberin monomers to the bulk SOC stock at silty site Banteln and the sandy site Essemühle was 38% higher in the deep-ploughed plots than at the reference plot, respectively, these differences were most visible in the subsoil of Essemühle. We conclude that when deep-ploughing enhances C stocks and root development, suberin SOC stocks increase as well, especially in the subsoil of sandy sites with low pH.

How to cite: Gocke, M., Burger, D., Schneider, F., Kappenberg, A., and Bauke, S.: Improved root development leads to higher root derived carbon stocks in formerly deep-plough soils - A biomarker-based approach, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-17904, https://doi.org/10.5194/egusphere-egu24-17904, 2024.

Ratios of non-traditional metal(loid) stable isotopes are a well-established tool in geosciences, used to semi-quantitatively trace geological transformation processes and biological cycling of mineral nutrients in the soil-plant system. Even though these processes also occur in agricultural systems, non-traditional metal(loid) isotope ratios are rarely used in agronomy. Their potential lies in revealing variations in isotope composition of metal elements like Fe and Mg between soil compartments and crops due to isotope fractionation occurring along the solubilization-uptake-translocation pathway [e.g., 1-5]. Agricultural management practices may influence isotope ratios in plant-available soil pools and, consequently, in plants.

The BonaRes-project Soil³ aims to enhance crop yield by optimizing nutrient and water use efficiency for field crops through subsoil management. We hypothesized that creating favorable conditions for crops in subsoil, like reducing physical resistance for roots or creating nutrient-rich hotspots, will stimulate crops to develop deeper root systems than without subsoil management. To examine our hypothesis, we altered subsoil conditions in field trials by cultivating deep-rooting pre-crops and employing technical subsoil improvement techniques through strip-wise deep loosening and organic matter injection. To assess the influence of standard management practices, such as liming, and possible nutrient deficiencies on isotope ratios in soil compartments and plants, we also investigated the isotope composition of nutrient pools in the deep subsoil of long-term field experiments and set up controlled pot experiments with defined nutrient conditions.

In the context of subsoil management experiments, we first conceptually explored the extent to which the Mg isotope composition of soil compartments and crops would be influenced by subsoil management. The novel outcome of this concept is that the Mg use efficiency of crops can be solely quantified from Mg stable isotope ratios, provided that agricultural lime is not applied to the fields [2]. Secondly, we used ⁸⁷Sr/⁸⁶Sr ratios to assess alterations in nutrient uptake depth in the subsoil managed plots. Our findings indicate that deep loosening with compost incorporation indeed deepened the nutrient uptake depth, with crops reaching previously unused nutrient reservoirs [6].

Regarding the influence of liming on Fe and Mg isotope compositions in a 100-year field experiment, we found a shift towards heavier Fe isotopes in rye, indicating an upregulation of the phytosiderophore complexation mechanism to counteract reduced Fe solubility at higher pH [5], and a pronounced shift towards lighter Mg isotopes in the exchangeable Mg pool, mainly attributed to an increased removal of heavy Mg isotopes by plant uptake [3]. A controlled pot experiment revealed that Mg deficiency altered the Mg isotope composition in wheat organs, indicating stress-induced shifts in Mg translocation within the plant [4].

Non-traditional metal(loid) stable isotopes hence provide powerful insights into biogeochemical cycling of nutrients that conventional analyses cannot detect.

[1] Wu et al., Earth-Science Reviews 2019, 190:323-352.

[2] Uhlig et al., Chem. Geol. 2022; 611:121114.

[3] Wang et al., Eur. J. Soil Sci. 2021; 72:300–312.

[4] Wang et al., Plant Soil 2020; 455:93–105.p

[5] Wu et al., Eur. J. Soil Sci. 2021; 72:289-299.

[6] Uhlig et al., Plant Soil 2023; 489: 613–628.

How to cite: Berns, A. E., Uhlig, D., Wu, B., Schweitzer, K., Bauke, S. L., Kuhn, A. J., Bol, R., and Wulf, A.: Exploring Non-traditional Metal(loid) Stable Isotope Tools for Agricultural Systems , EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-20148, https://doi.org/10.5194/egusphere-egu24-20148, 2024.

The subsoil, commonly defined as the soil beneath the tilled or formerly tilled soil horizon, contains large amounts of nutrients and water. Large fractions of these subsoil resources are not readily available to agricultural crops due to compacted layers of high bulk density. Although there are conventional methods for loosening compacted subsoils (e.g., mechanical subsoiling and deep ploughing), their effects are often quickly reversed or can even be harmful to the soil structure. Eventually, the brief enhancement in subsoil access for crops is often insufficient to justify the considerable expenses associated with the methods. To facilitate a more efficient use of subsoil resources, the Soil³ project for sustainable subsoil melioration derived a novel  approach, which is carried out in a single crossing of the field. First, the top soil of a 30 cm wide strip is excavated and deposited on the soil surface beside the strip, creating a furrow. The subsoil in this furrow (30-60 cm depth) is then loosened and intermixed with organic material (e.g., compost). After mixing, the excavated topsoil is lead back into the furrow, thus closing it again. The method therefore preserves the natural soil structure by not mixing the top and subsoil substrates, while the loosened subsoil structure is stabilized by incorporating organic material. Additionally, the operating costs are kept reasonable by only loosening the soil in a strip-wise manner.

Here, we use and extend the 3D functional-structural plant model CPlantBox to investigate the impact of the Soil³ method on root growth. On the soil side, we employ pedo-transfer functions to model the evolution of soil bulk density (soil setting) and the resulting changes in soil hydraulic properties in time. The pedo-transfer functions are parameterized based on data of the Soil³ field trials and are solved for different soil depths, as well as for the soil layers on and beside the melioration strips. In our model, we account for the time-dependent changes in soil hydraulic properties of all soil layers by implementing the usage of variable Van-Genuchten parameter sets within a single simulation run. Based on the parameterized soil domain, we simulate root growth and root water uptake from the different soil layers. Experimental data is used to parameterize general root growth parameters (e.g., root length density, planting density, transpiration). The explicit 3D root system architecture, however, is a result of the model, and its growth is modeled as a function of bulk density, water content and penetration resistance. By performing virtual replications of the field trials over multiple consecutive years, we can evaluate the impact and longevity of the subsoil melioration on root growth and its underlying processes.

How to cite: Selzner, T., Berns, A. E., Leitner, D., and Schnepf, A.: Model-based evaluation of the impact and longevity of a novel sustainable subsoil melioration method (Soil³ method) on root growth , EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-8136, https://doi.org/10.5194/egusphere-egu24-8136, 2024.

Cover crops (CC) are emerging as key tools in agrosystems, providing essential ecosystem services for climate change adaptation and mitigation. The great diversity of possible cover crops and climate scenarios makes it necessary to investigate how combinations of these two factors (cover crop type and climate scenario) affect agrosystems.

The experiment was carried out with mesocosms with soil of a Typic Calcixerept, inside a growth chamber with continuous control and programming of temperature, humidity, luminosity and ventilation. The climatic scenarios studied correspond to an average temperature increase of +3 ^oC and three levels of rainfall or water availability of: +10%, -5% and -20% with respect to the records of the reference area in the center of the Iberian Peninsula in the period 1950-2015.

In this work, the effect of five CC was evaluated: i.e. 1) without CC. 2) With CC composed by a Brassica (Camelina sativa L.). 3) with CC composed of a grass (Hordeum vulgare L.). 4) with CC composed of a legume (Vicia sativa L.) and 5) with CC composed of a mixture of the three species mentioned above. After the simulation from October 15 to January 1, the total population of Fungi (ITS), Archaea (16SA), Bacteria (16SB), electrical conductivity, macro and micro nutrients in the rhizospheric soil were evaluated. In addition, the biomass production and their macro and micronutrient concentrations were quantified.

The results obtained were modulated by water availability and microbial activity in the soil. In this sense, an increase in the population of ITS and 16SB was observed as the available water increased, especially at the +10% level. These results allow us to establish that the increase in moisture favored microbial activity in the study conditions, which is related to greater mineralization of organic matter. The CC composed of grasses and +10% rainfall stood out with a greater contribution of plant biomass, revealing the importance of soil moisture and the presence of grasses to increase the contribution of organic matter to the soil. On the contrary, the lower water availability (-20%) and the soil without cover produced an increase in electrical conductivity with respect to other treatments, and adversely affected numerous variables.

Among the cover crops, the legume and the mixture proved to be less affected by changes in the amount of available water. In addition, the mixture exhibited a mechanism that enabled it to achieve the highest Mg concentration in the plant. Possibly because the acquisition traits of the different species showed some complementarity.

For future research, the study of these CC will be carried out under other climatic scenarios, in order to elaborate a digital twin of each CC that will provide a more accurate information on their effects on the agrosystem according to the expected temperatures and water availability. This could help to choose the best cover crop for each scenario and objective.

How to cite: Enciso Santacruz, D., de Pablo Gonzalez, R., García, J. D., Navas, M., Hontoria, C., Moliner, A., Peregrina, F., and Mariscal-Sancho, I.: The use of cover crops in climate change scenarios, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-22056, https://doi.org/10.5194/egusphere-egu24-22056, 2024.

Spatial patterns where patches of high biomass alternate with bare ground occur in many resource-limited ecosystems. Especially fascinating are regular patterns, which are self-similar at a lag distance corresponding to the typical distance between patches. Regular patterns are understood to form autogenously through self-organization, which can be generated with deterministic reaction-diffusion models. Such models generate highly regular patterns, which repeat at the characteristic wavelength and are therefore periodic. Natural patterns do not repeat, as they are noisy and as the patch size and spacing vary. Natural patterns are therefore usually perceived as perturbed periodic patterns. However, the self-similarity of natural patterns decreases at longer lag distances, which indicates that their spatial structure is not a perturbed periodic structure originating through deterministic processes. Here, we provide an overview of our recent work on the spatial structure and formation of natural environmental spatial patterns as a basis for discussion: First, we develop a statistical periodicity test and compile a large dataset of more than 10,000 regular environmental spatial patterns. We find that neither isotropic (spotted) nor anisotropic (banded) patterns are periodic. Instead, we find that their spatial structure can be well described as random fields originating through stochastic processes. Second, we recognize the regularity as a gradually varying property, rather than a dichotomous property of being periodic or not. We develop a method for quantifying the regularity and apply it in a metastudy to a set of natural and model-generated patterns found in the literature. We find that patterns generated with deterministic reaction-diffusion models do not well reproduce the spatial structure of environmental spatial structure, as they are too regular. Third, we develop an understanding of pattern formation through stochastic reaction-diffusion processes, which incorporate random environmental heterogeneities. We find that regular patterns form through filtering of the environmental heterogeneities and identify stochastic processes which reproduce both isotropic and anisotropic patterns.

How to cite: Kästner, K., van de Vijsel, R. C., Caviedes Voullieme, D., and Hinz, C.: Unravelling the spatial structure of regular environmental spatial patterns , EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-3412, https://doi.org/10.5194/egusphere-egu24-3412, 2024.

A wildfire occurred in 2012 in one of the protected relic laurel forests of Europe (the National Park of Garajonay, Canary Islands). Soils from unburnt and burnt areas were studied and compared on its water repellence level at different soil moisture content from 2004 till 2023. 32 study sites and more than 100 soils were prepared under saturation conditions (sprayed of distilled water on the surface of each sample). Starting from saturation till oven-dried conditions, lower soil moisture contents were established in successive increments after the end of the WDPT test. The petri dishes were weighted at each step to determine the gravimetric soil water content (g g ^-1) by the thermogravimetric method at the end of the sequence. To describe the influence of soil moisture content on water repellency, three phases were distinguished. Phases I and II corresponded with the air-drying phase and phase III to the oven-drying phase.

Results of the study highlight that the water repellency of in both unburned and burnt sites strongly depended on the soil moisture content. After 11 years from the fire, the infiltration capacity of the soils showed improved levels of water repellency and in some cases total recovery. In order to reproduce the soil hydrophobic behavior under naturally occurring drying conditions (phases I and II), the time required for infiltration was modelled as a function of gravimetric moisture content during air-drying. Variability (standard deviation) increased with increasing times to infiltration (i.e. decreasing moisture content), which can be attributed to evaporation and soil hydraulic effects influencing the results during longer tests.

How to cite: Garcia-Santos, G., Puff, M., Kogler, C., Fernandez, A., and Eckmeier, E.: Influence of soil moisture content on water repellency after a forest burnt, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-19602, https://doi.org/10.5194/egusphere-egu24-19602, 2024.

The Hengduan Mountains (HDM) is one of the most biologically diverse mountain ranges on the planet, with exceptionally high levels of endemism. We expect that the geological and climate changes of the regions shaped endemism though dispersal and speciation processes by modulating landscape connectivity. Here, we characterise the plant endemism in the HDM, by mapping the distribution of 3,165 endemic species, representing approximately 25% of the total plant species richness. We show that endemic richness is highest along the southern front of the HDM, and especially concentrated along the Shangri-la Plateau and the three-river parallel region at elevations between 2,700 and 4,200 meters a.s.l. We demonstrate a geographically differentiated effect of connectivity on endemic richness and composition. In the endemic hotspot, we find a negative connectivity-diversity relationship, while we find a positive connectivity diversity relationship in the northern and southern HDM. Our result suggests a dominant role of isolation-induced allopatric speciation. Low connectivity may facilitate allopatric speciation in shaping distinct lineage in central HDM; while in the north of HDM, similar cold habitats in high elevation where habitats are more connected than the southern part, have likely facilitated species migration during the Quaternary glaciation. Thus, the degree of connectivity varied within HDM depending on their topographical configuration. Geographic contrasts in diversity further match endemic composition, which suggest the effect of geological history in shaping the diversity and composition of this exceptional flora. Overall, we conclude that landscape connectivity is a key driver of endemic plant speciation in HDM, explaining richness patterns that cannot be explained by temperature and other classic predictors.

How to cite: Yuan, Z.: Regional hotspots of Hengduan plant endemism inferring local speciation in response to connectivity, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-9893, https://doi.org/10.5194/egusphere-egu24-9893, 2024.

Coastal mangroves provide vital habitats for marine and coastal ecosystems while also stabilising coastlines, preventing erosion and mitigating the impact of storms. Sea-level rise poses a significant threat to these areas, causing submergence, vegetation changes, and hydrodynamic alterations. Sediment accretion can attenuate the effects of sea-level rise by promoting sedimentation. Mangroves trap sediments with their roots, which gradually create soil layers. The balance between soil accretion and sea-level rise will determine the mangrove's ability to adapt and survive. It is, therefore, crucial to determine the amount of water and sediments produced in the tributary catchment that reaches mangrove areas.

Moata'a is an urban village on the Upolu Island of Samoa, comprising around 300 to 500 households. It is home to a mangrove wetland that has been negatively impacted by human activities such as urban expansion, uncontrolled extraction of natural resources, pollution, and modification of input flows and tidal regime. Furthermore, Moata'a is susceptible to extreme weather conditions such as tropical cyclones, floods, and droughts, which may worsen as a result of climate change.

The amount of water and sediments that flow into the Moata'a mangrove area is influenced by the Vaisigano River. Moata'a is situated in the Vaisigano River's floodplain region, one of the primary rivers on Upolu Island. The Vaisigano River catchment is characterised by a hilly terrain covered with forests and a narrow coastline. During significant flooding events, water is transferred from the Vaisigano to the Moata'a catchment. Significant sediments can be discharged into the mangrove areas in these extreme circumstances.

This contribution presents a hydro-sedimentological assessment of the Moata’a’s mangrove catchment. The Soil & Water Assessment Tool (SWAT) was used to quantify the amount of water and sediment generated in the Moata’a’s catchment and the water and sediments produced by the Vaisigano catchment that are transferred to Moata’a’s mangroves during extreme events.

How to cite: Jorquera, E., Rodriguez, J. F., Saco, P. M., Quijano Baron, J. P., Breda, A., Sandi, S., Verdon-Kidd, D., and Nelson, F.: Assessing Sediment Delivery from Catchment Areas to Coastal Ecosystems in the Pacific Islands: A Study in an Urban Context, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-13758, https://doi.org/10.5194/egusphere-egu24-13758, 2024.

The release of organic substances from roots (exudates) to the soil system can induce changes in the mineralization rate of soil organic carbon (SOC) via so-called priming effects. Compared to other terrestrial ecosystems, mechanistic knowledge about priming effects in anoxic wetland soils is scarce, and few studies have investigated the composition and magnitude of root exudation in wetland plants. Given the disproportionate role of wetlands in the global soil carbon budget, this represents a critical knowledge gap in our understanding of terrestrial soil-climate feedbacks.

Here we present data from (1) a meta-analysis to summarize all quantitative and qualitative observations on wetland root exudation; and (2) exudate-surrogate incubation experiments testing for exudate effects on wetland SOC decomposition under anoxic conditions.

The meta-analysis shows that few comparable data on wetland exudation rates exist because extraction methods differ strongly, and only few species have been evaluated frequently. The data demonstrate that wetland plants not only release sugars, amino acids and organic acids into the rhizosphere, but also secondary compounds with a high allelochemical (e.g. gallic acid) or decomposition-hampering potential (e.g. phenolics). Their combined effect on the stability of soil carbon stocks is currently unpredictable on the ecosystem level. Our incubation experiments show that labile C inputs into an anoxic soil have a great potential to suppress SOC decomposition via negative priming. This finding contrasts to positive priming effects commonly found in oxic terrestrial soils and yields important implications for the stability of wetland SOC stocks in response to climate induced vegetation shifts.

How to cite: Krüger, N. and Mueller, P.: Exudate dynamics and rhizosphere priming in wetland ecosystems, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-9636, https://doi.org/10.5194/egusphere-egu24-9636, 2024.

Global warming and increasing air temperatures also result in rising soil temperatures. Although acceleration of soil organic carbon cycling can be expected, the order of magnitude and speed of adaptation of carbon cycling to warming still remains largely unknown. This is especially crucial in boreal peatlands, where large reserves of terrestrial carbon are stored and these systems are known for their vulnerability to environmental changes.

We investigated the organic matter composition in the SPRUCE (Spruce and Peatland Responses Under Changing Environments) experiment, where a boreal peatland was exposed to temperatures of up to +9°C and increased CO₂ concentration compared to control conditions in open top chambers. A broad set of molecular markers (e.g., free extractable and bound lipids, lignin, benzene polycarboxylic acids) was used to trace incorporation and cycling of organic matter in the peat profile down to three meters depth four years after the start of the experiment.

A strong response to increasing temperature was observed in the plant, microbial and peat chemical composition, the latter mainly in the acrotelm (0-30 cm) and partially also in the mesotelm (30-70cm). The response of the plant chemical composition was species-specific with the exception of nitrogen concentrations that increased for all plants. This is related to the stronger degradation of peat organic matter and thus increasing availability of nitrogen with rising temperature. All investigated molecular markers indicated a very fast response of carbon cycling in the whole acrotelm of the peat profile. This resulted from a dropping water table and thus more oxic conditions in the peat, which further enabled increasing shrub and tree root growth and increasing microbial abundance and activity. As a consequence of the more aerobic conditions, not only the comparatively easily degradable free extractable lipids, but also slow cycling polymeric substances such as suberin/cutin, lignin, and benzene polycarboxylic acids rapidly degraded and reflect an unexpectedly fast cycling of organic matter in the boreal peatland with increasing temperature. The acceleration of carbon cycling within the peatland with rising temperature is also reflected by the partial uptake of respired CO₂ by the plants as indicated by the bulk and compound-specific d¹³C composition of the plants. Overall, our results illustrate the fast alteration of organic matter cycling in a boreal peatland when exposed to increasing temperature.

How to cite: Wiesenberg, G. L. B., Ofiti, N., Huguet, A., Hanson, P. J., and Schmidt, M. W. I.: Rapid alteration of organic matter cycling in a boreal peatland in response to rising temperatures, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-22049, https://doi.org/10.5194/egusphere-egu24-22049, 2024.

Vegetation dynamics in dryland systems is highly dependent on soil moisture availability. Arid and semi-arid ecosystems are under the pressure of climate change and are facing overgrazing and logging, leading to increased degradation and desertification. The drylands of Mendoza, Argentina, are fragile ecosystems devoted to cattle breeding on native bushes and rangelands. Livestock farming relies on the productivity of natural resources, closely related to the monthly, annual, and seasonal rainfall, which is a critical driver of vegetation productivity and dynamics. However, the limited availability of precipitation data from gauging stations prevents a detailed analysis of the relationship between rainfall and vegetation. Therefore, satellite-estimated rainfall becomes a valuable information source to overcome this constraint.

This study aims to analyze the relationship between the antecedent accumulated precipitation (AAP) and the vegetation dynamics in terms of phenological metrics (Length of Growing Season – LGS; Peak of Growing Season – PGS; Amplitude of Growing Season – AGS) for four vegetation types in Southeast Mendoza, Argentina (Bush steppe with low land cover; Open Bush; Forest of Prosopis Flexuosa; and Psammophilous Grassland).

Vegetation parameters were derived using the software TIMESAT from Savitzky-Golay smoothing NDVI series of MODIS-Terra (MOD13Q1 V6.1) over 20 years (June 2000 to May 2020) and then correlated to AAP estimated by satellite using GPM (Global Precipitation Measurement) considering three time periods: Spring (accumulated precipitation of September to December), Spring plus Summer (September to February) and the duration of the Growing Season of each vegetation type.

All vegetation types showed a similar response and behavior regarding the AAP and vegetation dynamics metrics. The LGSs are similar, from 187 days for Psammophilous grassland to 198 days for Forest of Prosopis. However, there are differences at the start of the season. The PGSs (peak of NDVI) and the AGS show higher correlations to the spring and summer precipitation, while the LGS correlates to spring and accumulated precipitation during the growing season.

This information can help manage cattle grazing, avoid overgrazing, and manage production sustainably. Tracking vegetation responses to rainfall in space and time is of utmost importance for managing the limited resources,

How to cite: Brieva, C., Rodriguez, J., and Saco, P.: Vegetation Phenological Metrics and Accumulated Antecedent Precipitation (AAP) in dryland pastures., EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-14784, https://doi.org/10.5194/egusphere-egu24-14784, 2024.

Globally, agricultural soil management leads to soil organic carbon (SOC) losses, which contribute to increase atmospheric CO₂ concentrations and thereby climate change. Grassland introduction into cropping phases (ley grasslands) was suggested as an appropriate management strategy to reduce these losses. Here we examine the impact of ley grassland durations in crop rotations on soil organic carbon in temperate climate from 2005 to 2100. We considered two IPCC scenarios, RCP4.5 and RCP8.5, with and without atmospheric CO₂ enhancements. We used the DailyDayCent model and a long-term field experiment to show that ley grasslands increase SOC storage by approximately 10 Mg ha⁻¹ over 96 years compared with continuous cropping. Surprisingly, extending ley duration from 3 to 6 years does not enhance SOC, while it had a positive effect on plant residue accumulation in soil. Furthermore, in comparison with non-renewed grasslands, those renewed every three years demonstrated a notable increase in SOC storage, by 0.3 Mg ha⁻¹ yr⁻¹. These results may be explained by the enhanced input of root C in young grassland systems and its preferential contribution to soil organic matter formation. We concluded that management of root C inputs by ley grassland ploughing and renewal intervals is crucial for maximizing SOC stocks in agricultural soils, through balancing biomass carbon inputs during regrowth and carbon losses through soil respiration.

How to cite: Rumpel, C., Hu, T., Malone, S., and Chabbi, A.: Management of belowground inputs is crucial to maintain soil carbon storage under climate change, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-19210, https://doi.org/10.5194/egusphere-egu24-19210, 2024.