Eucalypt plantations may have negative consequences on soil properties, yet a comprehensive understanding of their impact on soil invertebrate communities is lacking. This knowledge gap constrains our ability to unravel the potential effects of these fast-growing plantations on soil functioning. Hence, to analyze the overall impact of eucalypt plantations on soil invertebrates and to determine the main factors influencing these effects, we conducted a meta-analysis of studies comparing eucalypt plantations with different land use types (i.e. native forests, other forestry plantations, croplands, grasslands, integrated production systems, and invasive copses). We assessed their effects on both the density (analyzing 26 studies with 143 comparisons) and diversity (examining 14 studies with 168 comparisons) of soil invertebrate communities. The impact of eucalypt plantations on the density and diversity of soil invertebrate communities did not show statistically significant differences when considering all land use types together. However, the effects of eucalypt plantations on soil invertebrate density and diversity varied based on the specific land use types considered for comparison. The density was lower in eucalypt plantations relative to other forestry plantations but higher than in grasslands and integrated production systems. Contrarily, diversity was lower in eucalypt plantations compared to native forests but higher compared to other forestry plantations. Furthermore, the impacts of eucalypt plantations on soil invertebrates relative to other forestry plantations were influenced by factors such as the type of other forestry plantation (angiosperms versus gymnosperms), mean annual temperature, and annual precipitation of the study sites. These findings suggest that the effects of eucalypt plantations on soil invertebrate communities are context-specific and heavily influenced by the diverse characteristics of the different land use types considered for comparison. Taking into account the specific management practices and environmental conditions within eucalypt plantations and other land use types can provide insight into how alterations in land cover affect soil invertebrate communities.

How to cite: Juan-Ovejero, R., Bartz, M. L. C., Baretta, D., Sousa, J. P., and Ferreira, V.: A meta-analysis addressing the effects of eucalypt plantations on soil invertebrate density and diversity, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-1454, https://doi.org/10.5194/egusphere-egu24-1454, 2024.

The most powerful tool to explore nutrient turnover in complex systems such as soils are stable isotope fractionation and labelling studies. This has been extensively used when investigating microbial carbon cycles by targeting the carbon stable isotopes in microbial phospholipid fatty acids (PLFA). However, exploring the role of mesofauna during carbon turnover in soil ecosystems has long been limited due to the small size and weight of those organisms and therefore issues in the detection and quantification of carbon stable isotope ratios. Only recently, carbon stable isotope analysis of fatty acids (FA) have been established and opened the window to include mesofauna into carbon turnover studies. We have used this new possibility after refining the available FA method to discover the role of microarthropods together with the microbial PLFA analysis. This study is to our knowledge the first, which has used ¹³C labelled plant material and has followed its incorporation into microbial PLFAs and microarthropodal FAs in a greenhouse experiment containing heavy metal contaminated and remediated soils.

Total microbial biomass and ¹³C incorporation into microorganisms was significantly increased and the PLFA pattern shifted after remediation of heavy metal contaminated soil. In accordance, the abundance of the microarthropodal groups Gamasina, Oribatida and Collembola were also increased, while Astigmata were not affected. The relative FA patterns of those groups differentiated significantly among each other, but were not influenced by soil treatment, meaning that the altered microbial PLFA pattern was not transferred into microarthropodal FA. However, the amount (nmol FA) per individuum was elevated in the heavy metal contaminated soil. In contrast, incorporation of ¹³C into FA was lower in contaminated soil in Gamasina, Astigmata and Collembola. ¹³C incorporation of Oribatida was at a constantly high level over the different soil treatments.

These first results revealed, that the relative FA pattern of the microarthropodal groups was not affected by changes in the microbial PLFA pattern due to soil treatments. Differences in the absolute FA amount per individuum and the ¹³C uptake were rather governed by the life and reproduction strategies, with higher fattiness and low abundance under adverse environmental conditions (contaminated soil), constant ¹³C incorporation in K-strategist (Oribatida) and higher ¹³C incorporation of mainly r-strategist (Gamasina, Astigmata and Collembola) under improved conditions.

How to cite: Watzinger, A., Christoph, N., Wissuwa, J., and Friesl-Hanl, W.: The role of microarthropodal groups in carbon turnover as revealed by 13C fatty acids analysis – method development and impact of heavy metal remediation, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-9456, https://doi.org/10.5194/egusphere-egu24-9456, 2024.

Sugar maple (Acer saccharum Marsh.) forests are the dominant ecosystems in southern Quebec (Canada) and are widely used for maple syrup production, wood products manufacturing, recreation, and sometimes converted to hybrid poplar plantations. Consequently, human footprints on these ecosystems are multifarious, with potential impacts on soil greenhouse gas (GHG) emissions. We studied the principal and interactive effects of three anthropogenic factors (liming, introduction of non-native earthworms, and tree litter quality) on soil CO₂ and N₂O emissions, and on related soil properties. Thirty-two PVC pipes (1.0 m x 30 cm dia.) were set upright and filled with homogenized soil collected from a sugar maple stand. Each of these mesocosms was assigned one of eight treatments from a 2×2×2 factorial array of three experimental factors (± liming, ± earthworms, maple vs. poplar litter), replicated in four complete blocks. Over the course of a 15-month trial, we measured soil CO₂ and N₂O emissions from each mesocosm. At the conclusion of the trial, we measured soil pH, % organic matter (SOM), mineralizable nitrogen (Nmin), water-stable aggregate index (WSAI), δ¹³C, and mineral-associated organic matter (C-MAOM) at each of four soil depths (0, 20, 40 and 60 cm). The effects of earthworms (+EW) and liming on the response variables were generally greater than the effects of litter types. Liming increased pH by 0.6 units in the soil surface layer. Treatments had negligible effects on SOM throughout the soil profile. Nmin increased by factors of ×15 and ×7 in the surface layer of the Liming and EW treatments respectively. In contrast, mineralizable NO₃^-/NH₄⁺ ratios were 125 and 80 in the EW and EW+Liming treatments respectively, and only 30 in the Liming and Control treatments, suggesting that nitrification was stimulated by soil mixing/aeration rather than by pH. Accordingly, cumulative N₂O emissions were higher in the EW and Ew+Liming treatments (500 and 250 mg N₂O-N m^-2, respectively) compared to the Control and Liming treatments (< 50 mg N₂O-N m^-2). Likewise, cumulative CO₂ emissions increased in the EW treatment and decreased in the Liming treatment relative to the Control; liming offset the positive effect of earthworms when both factors were combined.  Liming increased δ¹³C by 3‰ in the soil surface layer, hinting that lower CO₂ emissions in this treatment could have resulted from higher microbial processing of litter leading to more stable SOM. However, all treatments had no effect on C-MAOM, suggesting instead that higher δ¹³C in the Liming treatment resulted from higher ¹³C in the liming material compared to native soil C. Moreover, both Liming and EW treatments increased WSAI, thus refuting the premise that CO₂ and aggregate stability were related. We conclude that the spread of non-native earthworms in sugar maple forests of southern Quebec is potentially increasing soil N₂O and CO₂ emissions by up to one order of magnitude. Increased N₂O emissions are likely due to increased nitrification, whereas CO₂ emissions cannot be predicted by changes in C-stability. Liming could potentially be used to mitigate the positive effects of earthworms on soil GHG emissions.

How to cite: Jordan, F. and Ouimet, R.: Liming offsets the increase in soil greenhouse gas emissions due to non-native earthworms in sugar maple forests., EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-6967, https://doi.org/10.5194/egusphere-egu24-6967, 2024.

Tree species with leaf litter traits driving slow rates of leaf litter decomposition have traditionally been associated with accumulation of higher soil organic carbon (SOC) stocks than tree species with fast litter decomposition rates. This hypothesis has mainly been based on observations of thick C-rich forest floors under tree species associated with ectomycorrhizae (ECM). However, a recent hypothesis suggested that tree species with foliar litter traits conducive to fast decomposition will lead to more pronounced microbial transformation and stabilization of litter C. The latter tree species are often associated with arbuscular mycorrhizae (AM) and may enhance deeper incorporation of C by more active soil fauna communities and by higher belowground rates of litter input. The Danish multi-site common garden tree species experiment includes ECM and AM tree species that differ widely in traits such as foliar litter chemistry. The experiment has been studied over the last 15 years to document and explain soil C stocks supported by emerging studies of soil fauna and soil microbial community composition and functioning.

The six common European tree species formed distinct groups in soil carbon characteristics as well as in soil biota community composition and functioning that partly reflected their mycorrhizal association. Forest floor C stocks were consistent with the traditional perception of slowly decomposing leaf litter in ECM species being conducive to high C stocks. However, an intriguing pattern of higher C stocks in the mineral soil in AM tree species with high litter quality and characteristic soil biota functioning supported the recent microbial stabilization hypothesis and suggested deeper incorporation of C in more stable forms.

Based on new results on microbial, macro- and mesofauna communities and their functioning, and on repeated soil sampling, this talk will revisit the common garden experiments for a synthesis of processes and patterns in organic matter formation that may explain observed patterns in quantity and quality of SOC.

How to cite: Vesterdal, L., Steffens, C., Peng, Y., Zheng, H., Yi, H., and Hedênec, P.: Tree species effects on stocks and stability of soil carbon: Links to mycorrhizal association and soil biota composition and functioning, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-5867, https://doi.org/10.5194/egusphere-egu24-5867, 2024.

Soil nematodes, being the most abundant soil fauna, can significantly impact soil N mineralization via interaction with soil microorganisms. As a consequence, nematodes likely also influence soil N₂O production and emissions but the very few studies on this matter were carried out in simplified setups with single nematode species and in (highly) disturbed soil conditions. Here we measured soil N₂O emissions in a 74-day incubation experiment in the presence or absence of the entire soil nematode community with minimal disturbance of the soil microbial community and soil nutrients. This was e.g. evidenced by readily recovery of nitrifiers after the mild and selective sterilization and soil powder inoculation. N₂O emissions increased in the presence of nematodes, varying between soils +747.7 % in a loamy sand, +55.8 % in a loam, and +51.9 % in a silt loam cropland topsoil, in line with nematode abundance in these soils. In particular, the loamy sand soil showed an atypical N₂O emission peak at the time of high nematode abundance. Soil nematodes also increased net N mineralization by +8.4, +6.8 and +4.75 %, in these respective soils and to a smaller extent C mineralization as well. The extra soil nitrate buildup and the overall net stimulation of N mineralization by nematodes could not or just slightly explain the observed increased N₂O emissions. This research revealed the important role of soil nematodes in regulating N₂O emissions, and further stresses the need to consider the change in community composition and activity of denitrifiers, and connectivity of soil pores, rather than the stimulation of N mineralization as potential explanations for this role of nematodes.

How to cite: Hu, J., Kong, M., Françoys, A., Yarahmadi, F., Mendoza, O., Hassi, U., Gebremikael, M. T., Wesemael, W., Sleutel, S., and De Neve, S.: Increased N2O emissions by the soil nematode community cannot be fully explained by enhanced mineral N availability, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-11070, https://doi.org/10.5194/egusphere-egu24-11070, 2024.

Alleviation of functional limitations by soil fauna is key to climate feedbacks from arctic soils

Arctic soils play an important role in Earth’s climate system, as they store large amounts of carbon that, if released, could strongly increase greenhouse gas levels in our atmosphere. Most research to date has focused on how the turnover of organic matter in these soils is regulated by abiotic factors, and few studies have considered the potential role of biotic regulation. However, arctic soils are currently missing important groups of soil organisms, and here, we highlight recent empirical evidence that soil fauna presence or absence is key to understanding and predicting future climate feedbacks from arctic soils. We propose that the arrival of certain soil fauna into arctic soils may introduce “novel functions”, resulting in increased rates of, for example, nitrogen cycling, litter fragmentation, or bioturbation, and thereby alleviate functional limitations of the current soil organism community. This alleviation can greatly enhance decomposition rates, in parity with effects predicted due to increasing temperatures. We base this argument on a series of emerging experimental evidence suggesting that the dispersal of until-then absent micro- meso-, and macroorganisms into new regions and newly thawed soil layers can drastically affect soil functioning. These new observations make us question the current view that neglects organism-driven “alleviation effects” when predicting future feedbacks between arctic ecosystems and our planet’s climate. We therefore advocate for an updated framework in which soil biota and the functions by which they influence ecosystem processes become essential when predicting the fate of soil functions in warming arctic ecosystems.

How to cite: Krab, E. J., Blume-Werry, G., Klaminder, J., and Monteux, S.: Alleviation of functional limitations by soil fauna is key to climate feedbacks from arctic soils, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-3873, https://doi.org/10.5194/egusphere-egu24-3873, 2024.

The soil microbiome is widely recognized as an important driver of soil carbon (C) cycling but the role of soil fauna is largely overlooked. It is proven that microbivores, e.g., bacterivorous nematodes, can alter the microbiome composition and activity, but the microbivores themselves can be controlled by their predators. How these higher trophic interactions impact the soil microbiome, through trophic cascades, remains to be investigated, as well as the consequences for soil C cycling.

We tested the existence and direction of trophic cascades in soil food webs by manipulating the presence of bacterivorous-dominated nematode communities and their predators (nematode-feeding mite Gaeolaelaps aculeifer) in a full factorial design. After microbial re-inoculation of sterilized grassland soil and soil food web reconstruction, we monitored the decomposition of added grass litter and associated C mineralization during five weeks. We also characterized the soil microbiome composition by phospholipid fatty acid analysis and 16S sequencing.

While the presence of nematodes mostly did not affect C cycling, the addition of predators decreased C mineralization by 10 %. However, litter decomposition rates were unaffected by soil food web composition. Taken together, these results suggest that the presence of predators may result in enhanced soil C stabilization, at least in the short term. The presence of predators also resulted in a shift in microbiome composition, notably with higher Gram(+):Gram(-) ratios, but no change in microbial biomass, suggesting that nematodes may shift their diet because of predation. Our results confirm that the effects of nematodes and their predators on the soil microbiome are not additive and that predators can alter soil C cycling trough trophic cascades. As predators are often sensitive to land use change and intensification, these findings suggest that loss of belowground predators may result in increased C losses following litter decomposition.

How to cite: Lejoly, J., Wang, Y., van Hoof, E., Favre, V., Quist, C., Geisen, S., and Veen, C.: Trophic cascades in simplified soil food webs and consequences for carbon cycling, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-7897, https://doi.org/10.5194/egusphere-egu24-7897, 2024.

To understand carbon dynamics and how it is affected by ongoing climate change, we need a better appreciation of the belowground ecological interactions driving plant allocation patterns and ecosystem carbon fixation. It has become increasingly clear that belowground root inputs contribute significantly more to soil carbon sequestration than aboveground plant inputs. Yet, current understanding of the role of belowground root herbivory in ecosystem carbon dynamics is weaker than that of aboveground herbivory. We addressed this gap by merging three complementary and novel areas of research, namely testing how: (1) biotic interactions between plants and nematode herbivores affect belowground biomass allocation in grasses; (2) how these biotic interactions and their consequences for biomass allocation are modified by a pervasive perturbation, namely drought, which is becoming more intense and frequent; and (3) how belowground responses vary across contrasting ecosystems. Results of complementary controlled and multi-site field experiments showed that: (1) nematode root herbivory modulates the relationship between water availability and belowground biomass allocation; (2) drought-induced increases in nematode root herbivory impede plants from increasing biomass allocation to roots under drought; and (3) these nematode effects are greater in magnitude in mesic compared to semiarid and arid grasslands. These findings suggest that the fate of carbon in mesic ecosystems under increasing drought frequency is highly influenced by nematode herbivores in the soil, and encourage investigations into the unknown consequences for soil carbon formation and persistence.

How to cite: Franco, A. and Gherardi, L.: The influence of belowground nematode herbivory on carbon allocation in drought-prone ecosystems, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-10509, https://doi.org/10.5194/egusphere-egu24-10509, 2024.

The dominant paradigm is that nitrogen cycles from plants to soil organic matter, being released in mineral form in the soil after organic matter is decomposed by microbes to be taken up again by plants. It is generally held that the process of decomposition is the rate-limiting step in the cycle. Ground dwelling macroinvertebrates may play a large role in ecosystem function by mediating microbe decomposition via predation and could be key links between plant litter and nitrogen availability in soil nutrient cycles. Ground beetles (Carabidae) are an abundant family of soil invertebrates that prey on groups of decomposing invertebrates. The goal of this study was to develop how predation from ground beetles contributes to nitrogen cycling as forests age. We hypothesized that ground beetles in young and old forests would indirectly impact available nitrogen. Our approach to addressing predator impacts on nitrogen cycling in forest soils was an experiment in young and old forest stands at Yale-Myers Forest in the northeastern United States using mesocosm cages stocked with predatory and detritivore ground beetles to create a trophic cascade over 68-days. Both forest sites had five blocks of three clustered treatments (n = 30). Treatments consisted of a control, detritivore, and predator and we took soil cores in each cage to assess available nitrogen. We used standard mesocosm cages that were designed for research on arthropod trophic interactions in ecosystems 1 m², 0.8 m tall cylindrical mesocosms constructed with a scaffolding covered with fine mesh aluminum stocked with live beetles. We conducted a series of linear mixed-effect models in RSudio from the nlme package and lme() function in R Studio to predict the delta nitrogen mineralization rate by treatment in both young and old forests separately. We used ground beetle treatment as a fixed effect and block as a random effect to account for variation in microsite differences. Here we show differences in available nitrogen between forest types (P-value = 0.03). Our hypothesis that predators would impact available nitrogen was supported in young forests. Net nitrogen mineralization (P-value = 0.007) was consistently higher in the predator treatments compared to the control. In conclusion, this study suggests predator top-down control may be important for soil nitrogen availability in temperate forest soil via mediating microbe decomposition. Macroinvertebrates and their food web interactions in the soil should be further investigated and included in soil biogeochemical models.

How to cite: Lienau, J., Duguid, M. C., and Schmitz, O. J.: Ground beetles trophic interactions alter available nitrogen in forest soils, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-729, https://doi.org/10.5194/egusphere-egu24-729, 2024.

Soil biogeochemical cycles are regulated by soil food webs. However, variation of soil food web structure and functioning across key environmental gradients remains unknown, hampering generalisations of any suggested links between fauna and biogeochemistry. Here, we used two complementary approaches to quantify soil animal food web variation across forest types, from southern taiga to rainforests. First, we applied the energy flux approach to explore patterns of energy distribution across micro-, meso- and macrofauna. We showed that tropical soil food webs have consistently higher energy flux, proportionally higher predation rates (31 vs 18-27% of the total energy flux) and relied more on the plant energy channel (21 vs 10%), but less on the bacterial (5 vs 9-18%) and litter energy channels (14 vs 18-32%), than temperate soil food webs. Second, we compiled a large database (>8000 records) of stable isotope composition of soil animals to see how detritivory and microbivory in soil animal communities change with environmental temperature and litter quality. Despite little effect of temperature, shift in ¹⁵N concentrations suggested that in most cases low litter quality (high %C and low %N) result in a switch from feeding directly on litter to feeding on microorganisms. Thus, soil animals change their functional role from competitors to consumers of microbes. Our studies show how the functioning of soil animal food webs changes across biomes with different climate and litter quality and summarise functional roles animals play in different biomes.

How to cite: Potapov, A., Thurikov, S., Scheu, S., and Tiunov, A.: Structure and functioning of soil animal food webs across temperate and tropical forests, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-7464, https://doi.org/10.5194/egusphere-egu24-7464, 2024.