Data from: Disentangling plant and soil microbial controls on carbon and nitrogen loss in grassland mesocosms

1. It is well known that plant–soil interactions play an important role in determining the impact of global change phenomena on biodiversity and ecosystem functioning. Little is known, however, about the individual and relative importance for carbon (C) and nitrogen (N) cycling of non-random changes in plant and soil communities that result from global change phenomena, such as fertilization and agricultural intensification. 2. We set up a field-based mesocosm experiment in which we re-inoculated soil with contrasting microbial communities taken from extensively managed and from intensively managed grasslands. In a full-factorial design, we subsequently established plant communities representative of intensively and extensively managed grasslands and imposed a fertilization treatment. We then measured plant biomass and diversity, and leaching of C and N as key measures of C and N loss. 3. We hypothesized that non-random changes in both microbial and plant communities would impact C and N leaching, but via different mechanisms. We predicted that plant communities representative of extensively managed grassland would reduce C and N leaching directly through increased water or N uptake, or indirectly via promoting microbial communities that immobilize C and N, whereas plant communities of intensively managed grassland would have the opposite effect. We also hypothesized that microbial communities of extensively managed grassland would feed back positively to plant diversity and that ‘matching’ plant and microbial communities would reduce C and N leaching. 4. We found that both plant and microbial communities from extensively managed grassland reduced C and N leaching, especially when ‘matched’. Plant community effects on C and N leaching operated directly through root C inputs and N uptake, rather than through changes in soil microbial communities. In contrast, microbial communities modified C and N leaching both directly by immobilization and indirectly through modifying plant community composition. 5. Synthesis. Our results show that changes in plant and microbial communities both individually and interactively modify C and N loss from grasslands. Moreover, our results suggest that soil microbial communities typical of extensively managed grassland might counteract, or delay, the negative consequences of fertilization on plant diversity and ecosystem functioning.

1. 众所周知，植物-土壤相互作用（plant–soil interactions）在决定全球变化现象对生物多样性和生态系统功能的影响方面发挥着关键作用。然而，针对施肥、农业集约化等全球变化现象所引发的植物与土壤群落的非随机变化，其在碳（C）、氮（N）循环中的个体作用与相对重要性，目前仍缺乏深入认知。
2. 本研究搭建了基于野外的中宇宙实验（field-based mesocosm experiment）：从粗放管理与集约化管理的草地中获取具有显著差异的微生物群落，并将其重新接种至土壤基质中。随后采用完全析因设计（full-factorial design），建立了分别代表集约化与粗放管理草地的植物群落，并施加施肥处理。最终测定了植物生物量、植物多样性，以及碳、氮淋溶量，以此作为碳、氮流失的核心观测指标。
3. 我们提出如下研究假说：微生物与植物群落的非随机变化均会对碳、氮淋溶过程产生影响，但二者的作用机制存在差异。我们预测，代表粗放管理草地的植物群落，可通过增强水分或氮素吸收直接降低碳、氮淋溶，或通过促进固持碳、氮的微生物群落间接实现该效果；而集约化管理草地对应的植物群落则会产生相反效应。此外，我们还提出补充假说：粗放管理草地的微生物群落可对植物多样性产生正向反馈，且“匹配”的植物与微生物群落可进一步降低碳、氮淋溶水平。
4. 研究结果表明，来自粗放管理草地的植物与微生物群落均可降低碳、氮淋溶，尤其是当二者“匹配”时，该抑制效果尤为显著。植物群落对碳、氮淋溶的影响主要通过根系碳输入与氮素吸收直接发挥作用，而非通过改变土壤微生物群落结构实现。与之相反，微生物群落既可通过固持作用直接调控碳、氮淋溶，也可通过改变植物群落组成间接发挥调控功能。
5. 综合与结论。本研究结果显示，植物与微生物群落的变化，无论是单独作用还是交互作用，均可改变草地生态系统的碳、氮流失过程。此外，本研究结果还暗示，典型粗放管理草地的土壤微生物群落，或可抵消或延缓施肥对植物多样性与生态系统功能带来的负面影响。