Andrey S. Zaitsev

Diversity of the Soil Biota in Burned Areas of Southern Taiga Forests (Tver Oblast)

Relations between soil biota diversity and its contribution to the performance of some ecosystem functions were assessed based on the results obtained in undisturbed and burned spruce forests near the Central Forest Nature Biosphere Reserve (Tver oblast). In August 2014, in two 4-year-old burned areas, abiotic parameters of the soils, indicators of the state of the microbial communities, the number, taxonomic diversity, and the abundance of the main groups of soil invertebrates (testate amoebae, nematodes, enchytraeids, mites, collembolans, and the mesofauna as a whole) were determined. In the soils of the burned areas, higher CO2, CH4, and N2O emissions were observed. The number of bacterial cells remained similar, and the total length of active mycelium was not significantly different. All this implies a certain intensification of biogenic processes promoting the mobilization of carbon and nitrogen after fire. The number of most of the groups of soil animals was lower (not always significantly) in the burned area than that in the soils of the undisturbed forests. The changes in the taxonomic diversity were specific for each taxon studied. Overall, the diversity of invertebrates was related to the litter thickness. However, the high taxonomic diversity of soil fauna did not always correspond to the active functioning of the ecosystem. Thus, for some taxa, a quite close correlation was found, for instance, between the total number of species (of testate amoebae in particular) and the berry crop, as well as between the soil mesofauna population and the dead wood stock. The total diversity of the investigated taxa included in the detrital trophic web was the most reliable indicator of the carbon stock in the burned areas.

Land-use type and intensity differentially filter traits in above- and below-ground arthropod communities

Along with the global decline of species richness goes a loss of ecological traits. Associated biotic homogenization of animal communities and narrowing of trait diversity threaten ecosystem functioning and human well-being. High management intensity is regarded as an important ecological filter, eliminating species that lack suitable adaptations. Below-ground arthropods are assumed to be less sensitive to such effects than above-ground arthropods. Here, we compared the impact of management intensity between (grassland vs. forest) and within land-use types (local management intensity) on the trait diversity and composition in below- and above-ground arthropod communities. We used data on 722 arthropod species living above-ground (Auchenorrhyncha and Heteroptera), primarily in soil (Chilopoda and Oribatida) or at the interface (Araneae and Carabidae). Our results show that trait diversity of arthropod communities is not primarily reduced by intense local land use, but is rather affected by differences between land-use types. Communities of Auchenorrhyncha and Chilopoda had significantly lower trait diversity in grassland habitats as compared to forests. Carabidae showed the opposite pattern with higher trait diversity in grasslands. Grasslands had a lower proportion of large Auchenorrhyncha and Carabidae individuals, whereas Chilopoda and Heteroptera individuals were larger in grasslands. Body size decreased with land-use intensity across taxa, but only in grasslands. The proportion of individuals with low mobility declined with land-use intensity in Araneae and Auchenorrhyncha, but increased in Chilopoda and grassland Heteroptera. The proportion of carnivorous individuals increased with land-use intensity in Heteroptera in forests and in Oribatida and Carabidae in grasslands. Our results suggest that gradients in management intensity across land-use types will not generally reduce trait diversity in multiple taxa, but will exert strong trait filtering within individual taxa. The observed patterns for trait filtering in individual taxa are not related to major classifications into above- and below-ground species. Instead, ecologically different taxa resembled each other in their trait diversity and compositional responses to land-use differences. These previously undescribed patterns offer an opportunity to develop management strategies for the conservation of trait diversity across taxonomic groups in permanent grassland and forest habitats.

Regional Conditions and Land-Use Alter the Potential Contribution of Soil Arthropods to Ecosystem Services in Grasslands

We investigated the impact of regional conditions and land-use intensity on eight selected arthropod taxa of Mesostigmata (Parasitidae), Oribatida (3 species), Collembola (1 species), Chilopoda (2 species) and Diplopoda (1 species) sampled in differently managed permanent grasslands of three German study regions. By jointly analyzing changes in abundance and trophic behavior (measured as natural variation in 15N/14N and 13C/12C ratios) we intended to develop a framework for evaluating the impact of local and regional conditions on the ecosystem services delivered by soil animals (mainly decomposition- and predation-related services). The investigated taxa could be assorted to three major groups: (1) numerical response only, (2) numerical and trophic response and (3) trophic response only. Since the combination of taxa assembled in the individual groups does not correspond to any of the conventional soil ecological classification systems, this grouping offers a new approach for analyzing soil communities. The complementing consideration of both the direction of the numerical response and the type of the trophic response (change of the basal food source vs. trophic level shift vs. variations in isotopic niches) provided a differential insight into the effect of management and geographic differences on soil arthropods. It could be shown that the effect of land-use on the abundance of detritivorous microarthropods varies among regions, but does not induce any changes in feeding behavior. Our findings on Parasitidae indicate that carnivorous microarthropods exert substantial predation pressure on soil mesofauna and may be quite resistant to environmental changes due to high trophic flexibility. If conditions are favorable, centipedes may reach comparatively high densities in permanent grasslands and could be very important for controlling belowground pests. Concerning millipedes, isotopic signatures suggest that some species could exert a substantial disservice by feeding on roots over a wide range of land-use intensities and regional conditions. We conclude that the many consistent and significant effects found in our study support our contention that the combined analysis of numerical and trophic responses provides a promising framework for designing spatially explicit models that quantify the impact of human interventions on the delivery of ecosystem services by the soil fauna.

Belowground Tritrophic Food Chain Modulates Soil Respiration in Grasslands

Abstract Edaphic biota significantly affects several essential ecological functions such as C-storage, nutrient turnover, and productivity. However, it is not completely understood how belowground animal contribution to these functions changes in grasslands subject to different land use types. A microcosm experiment was carried out to test the effect of a tritrophic food chain on CO2 release from grassland soils. Soil was collected from three differently managed grassland systems (meadow, pasture, and mown pasture) located in three distinct German regions that cover a north-south gradient of approximately 500 km. The tritrophic food chain comprised natural edaphic microflora, nematodes, and predatory gamasid mites. The experimental design involved a full factorial combination of the presence and absence of nematodes and gamasid mites. Nematodes significantly increased the CO2 emissions in most treatments, but the extent of this effect varied with land use type. The fact that grazing by nematodes stimulated the metabolic activity of the edaphic microflora over a wide range of grassland soils highlighted the critical impact of the microfauna on ecosystem services associated with soil organic matter dynamics. Gamasids slightly amplified the effect of nematodes on microbial metabolic activity, but only in the pastures. This effect was most probably due to the control of nematode abundance. The fact that gamasid addition also augmented the impact of environmental conditions on nematode-induced modulation of soil respiration highlighted the need for including land use differences while evaluating soil fauna contribution to soil processes. To conclude, the differential response of the investigated tritrophic food chain to different grassland management systems suggests that adverse effects of land use intensification on important soil processes such as atmospheric C-release could potentially be reduced by using management methods that preserve essential features of the belowground food web.

Reduced functionality of soil food webs in burnt boreal forests: a case study in Central Russia

Functionality of soil food webs after forest fires remains generally unexplored. We address this question by studying both burnt and unburnt spruce forests in Central European Russia (Tver Region). In August 2014 we sampled two spatially distant blocks consisting of forest areas burnt in 2010 and the respective unburnt controls. We analyzed biomass and structure of soil food webs as well as carbon mobilization with respect to carbon stocks in the dead wood, litter and soil after burning. The biomass of soil fauna was moderately reduced in the burnt plots. For some groups like testate amoebae and enchytraeids, however, this decrease was highly significant and corresponded with the decreased C-stock in litter. For the other taxa changes in biomass were insignificant. At the same time C-flow through the soil food web after fire was strongly reduced mainly due to the reduction of biomass of active fungi and secondary decomposers. The overall consumption rate of detritus by the soil food web strongly decreased in the burnt forests and was maintained predominantly by the decomposition activity of bacteria instead of fungi. This resulted in the reduction of the total soil food web functionality related with C-mobilization in the forests four years after a fire event.Brief SummaryWe compared rates of carbon mobilization by soil food webs in burnt and unburnt boreal forests in Central Russia. Despite of only slight decrease in soil animal biomass, consumption rate of carbon in the soil food webs after fire was considerably lower and mainly associated with soil bacteria instead of fungi.