Contrasting effects of deadwood and gaps on the trophic structure of forest soil microarthropods

Understanding the mechanisms driving forest biodiversity is challenging, especially in soil. Trophic niche is the most important perspective to understand how biodiversity changes with disturbances. Deadwood input and gap formation are major disturbances resulting from tree mortality. Both alter the ecological niches of forest organisms, yet their individual and interactive effects on soil animals remain unclear. Trophic diversity, that is the area of trophic niches occupied by organisms, links to the resource processing within food webs and, consequently, to ecosystem functions. Changes in trophic diversity of Collembola communities may result both from changes in species composition and from trophic shifts of individual species. To investigate how the trophic structure of soil fauna responds to forest disturbances, we examined trophic niches of Collembola across three regions in Germany, as influenced by deadwood addition and gap formation using stable isotope analysis ( 13 C, 15 N). Changes in the trophic structure of Collembola associated with deadwood addition and gap formation were distinct and independent. Deadwood addition resulted in higher trophic level (Δ 15 N values) and greater trophic diversity of Collembola communities. These shifts were likely driven by increased habitat heterogeneity resulting in higher trophic differentiation (rather than higher species richness) of Collembola communities. The results highlight the importance of habitat structure in driving soil animal functional diversity. By contrast, gap formation promoted the growth of understorey plants, leading to increased use of plant‐derived resources (lower Δ 13 C values) by Collembola. Further, gap formation reduced the trophic diversity of euedaphic (soil dwelling) Collembola pointing to trophic homogenisation, likely driven by increased use of root‐derived resources from understorey plants, and this also was accompanied by higher biomass of euedaphic Collembola in forest gaps. Overall, our findings highlight that deadwood addition and gap formation affect the trophic structure of detritivore communities in an independent way, with deadwood enhancing habitat heterogeneity and trophic differentiation, while gap formation resulting in trophic homogenisation and increased resource supply to euedaphic Collembola. Thereby, deadwood addition and gap formation complement each other in affecting the trophic structure of detritivore soil animals and thereby their functioning. Read the free Plain Language Summary for this article on the Journal blog.