Phosphorus addition increases the total abundance and favors microbivorous Collembola in subalpine plantation forest

Abstract

Collembola are among the most abundant microarthropods in virtually all soils. Typically, taxonomic units based on life forms or trophic guilds are treated as proxies for functional groups to explore microarthropod responses to environmental changes. However, this approach may be misleading for understanding the role of Collembola as their ecological functions in soil food webs are affected by both life form and trophic group. In this study, we examined how Collembola communities respond to the addition of different levels of phosphorus (0, 50, 150 and 300 kg ha−1 yr−1) in subalpine forest on the eastern Tibetan Plateau eight years after establishment of the phosphorus enrichment gradients. Consistent with our expectations, phosphorus addition increased Collembola total abundance and this was closely related to decreased litter N/P ratio, increased relative abundance of saprotrophic fungi as well as increased infection rate of plant roots by ectomycorrhizal fungi. Notably, the response varied between Collembola functional groups defined by combining information on life forms and trophic groups. Epedaphic detritivores, hemiedaphic microbivores and euedaphic microbivores were most strongly affected by litter nutrient quality (N/P ratio), saprotrophic and ectomycorrhizal fungi, respectively. Furthermore, the results suggest that hemiedaphic microbivore Collembola preferentially fed on saprotrophic fungi in phosphorus addition treatments, which likely was due to increased relative abundance of saprotrophic fungi. By contrast, euedaphic microbivore Collembola mainly fed on ectomycorrhizal fungi indicating that they are closely linked to root-derived resources. Overall, the results highlight that Collembola functional groups respond differently to changes in the quality and availability of food resources. Furthermore, the results suggest that considering both life form and trophic group information allows to effectively link changes in Collembola community composition to changes in their functions.