Divergence of feeding channels within the soil food web determined by ecosystem type

Abstract

Understanding trophic linkages within the soil food web (SFW) is hampered by its opacity, diversity, and limited niche adaptation. We need to expand our insight between the feeding guilds of fauna and not just count biodiversity. The soil fauna drive nutrient cycling and play a pivotal, but little understood role within both the carbon (C) and nitrogen (N) cycles that may be ecosystem dependent. Here, we define the structure of the SFW in two habitats (grassland and woodland) on the same soil type and test the hypothesis that land management would alter the SFW in these habitats. To do this, we census the community structure and use stable isotope analysis to establish the pathway of C and N through each trophic level within the ecosystems. Stable isotope ratios of C and N from all invertebrates were used as a proxy for trophic niche, and community-wide metrics were obtained. Our empirically derived C/N ratios differed from those previously reported, diverging from model predictions of global C and N cycling, which was unexpected. An assessment of the relative response of the different functional groups to the change from agricultural grassland to woodland was performed. This showed that abundance of herbivores, microbivores, and micropredators were stimulated, while omnivores and macropredators were inhibited in the grassland. Differences between stable isotope ratios and community-wide metrics, highlighted habitats with similar taxa had different SFWs, using different basal resources, either driven by root or litter derived resources. Overall, we conclude that plant type can act as a top-down driver of community functioning and that differing land management can impact on the whole SFW.

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

“…We therefore calibrated isotope values for soil arthropods as difference between the aboveground plant and soil arthropod samples (δ plant -δ animal) at a particular site (expressed by the notion 15 N or 13 C). The resulting enrichment values for nitrogen and carbon isotopes suggest that values are comparable to calibration by litter samples (Crotty et al, 2014; Mesostigmata N: +6‰, C: +3‰; Listed are the major taxonomic groups, the trophic levels (D, decomposer; P, predator), the Pearson correlation coefficient between δ 15 N values in animal samples and plant samples (R), the number of sites within each region for which abundances were sufficiently high to analyze ratios of naturally occurring C and N stable isotopes and the mean abundances of each taxonomic group per region (n, individuals m −2 ) ± standard errors of the mean for each region and taxon.…”

“…Regional differences in dietary niche size and overlap nevertheless indicate a substantial influence of geographic conditions on food exploitation by most microarthropods (cf. Crotty et al, 2014). Concerning the detritivorous mesofauna, however, a significant regional shift of the basic food source could only be established for the oribatid mite T. trimaculatus (group 3, trophic response only).…”

“…The interplay between regional conditions and local land-use is therefore likely to modify the contribution of edaphic animals to ecosystem services. It remains unknown, however, to what extent such changes manifest themselves through numerical and/or functional responses of the soil fauna to large-and small-scale differences in environmental conditions (Barrios, 2007;Crotty et al, 2014).…”

“…This, for example, has been demonstrated for the effects of fertilization (King and Hutchinson, 1980;Birkhofer et al, 2008), grazing (King and Hutchinson, 1976;Ponge et al, 2015), and cutting (Jensen et al, 1973;Lemanski and Scheu, 2015). As a consequence, critical shifts within soil food webs may occur (Haubert et al, 2009;Birkhofer et al, 2011;Crotty et al, 2014;Klarner et al, 2014). Unfortunately, the greening measures recently implemented by the European Commission to protect and maintain species-rich permanent grasslands do not take such human interventions into account (Common Agricultural Policy 2013: Regulation No 1307.…”

Fire affects root decomposition, soil food web structure, and carbon flow in tallgrass prairie

“…This technique has been used to study plant-C utilization by microbial communities in soils by examining 13 C incorporation into microbial phospholipid fatty acids (PLFAs; e.g., Denef et al, 2009;Rubino et al, 2010;Kohl et al, 2015;Soong et al, 2016). Also, natural abundances of 13 C and 15 N have been useful for studying structures of soil faunal communities (e.g., collembolans, earthworms, enchytraeids, arthropods, gastropods, and nematodes; Chahartaghi et al, 2005;Albers et al, 2006;Goncharov et al, 2014;Crotty et al, 2014;Kudrin et al, 2015). Furthermore, C flow though soil faunal trophic groups can be traced and quantified using 13 C in labeling experiments (Albers et al, 2006;Pollierer et al, 2007;Elfstrand et al, 2008;Ostle et al, 2007;D'Annibale et al, 2015;Gilbert et al, 2014).…”