Priority effects are interactively regulated by top-down and bottom-up forces: evidence from wood decomposer communities

Both top-down (grazing) and bottom-up (resource availability) forces can determine the strength of priority effects, or the effects of species arrival history on the structure and function of ecological communities, but their combined influences remain unresolved. To test for such influences, we assembled experimental communities of wood-decomposing fungi using a factorial manipulation of fungivore (Folsomia candida) presence, nitrogen availability, and fungal assembly history. We found interactive effects of all three factors on fungal species composition and wood decomposition 1 year after the fungi were introduced. The strength of priority effects on community structure was affected primarily by nitrogen availability, whereas the strength of priority effects on decomposition rate was interactively regulated by nitrogen and fungivores. These results demonstrate that top-down and bottom-up forces jointly determine how strongly assembly history affects community structure and function.下行控制（top-down，即牧食作用）与上行控制（bottom-up，即资源可获得性）均可调控优先效应（priority effects）的强度——优先效应即物种到达历史对生态群落结构与功能的影响，但二者的联合作用仍未得到明确解析。为检验此类联合作用，我们通过析因操控食真菌动物（fungivore，Folsomia candida）的存在与否、氮素可获得性以及真菌群落组装历史，构建了木材分解真菌的实验群落。研究发现，在真菌接种一年后，三种因素对真菌物种组成与木材分解过程均存在交互效应。优先效应对群落结构的影响强度主要受氮素可获得性调控，而其对分解速率的影响强度则由氮素与食真菌动物共同交互调控。本研究结果表明，下行与上行控制因子共同决定了群落组装历史对生态群落结构与功能的影响强度。