Data from: Soil biota suppress positive plant diversity effects on productivity at high but not low soil fertility

1. Plant community productivity commonly increases with increasing plant diversity, which is explained by complementarity among plant species in resource utilization (complementarity effect), or by selection of particularly productive plant species in diverse plant communities (selection effect). Recent studies have also shown that soil biota can drive the positive plant diversity–productivity relationship by suppressing productivity more in low- than in high-diversity plant communities. However, much remains unknown about whether soil fertility plays a role in determining how soil biota affect plant diversity–productivity relationships. 2. We hypothesized that under high soil fertility conditions, negative soil biota effects dominate, which reduces plant monoculture biomass more than that of high-diversity plant communities. Conversely, under low soil fertility conditions, we hypothesized positive soil biota effects dominate, which facilitates plant resource partitioning and enhances community-level biomass in high-diversity plant communities. Hence we expected positive plant diversity–community productivity relationships under low and high soil fertility conditions but caused by different mechanisms. 3. We tested these hypotheses using woody seedlings and set up plant assemblages with four species richness levels (one, two, four and eight species), and grew them in sterilized and unsterilized (sterilized soil + living soil inoculum) soils at two nutrient levels (low vs. high fertility). 4. We found that at high fertility negative soil biota effects dominated and suppressed plant community biomass more in high-diversity plant communities than in monocultures, resulting in reduced complementarity effects of diverse plant communities and a non-significant plant species richness–community biomass relationship in unsterilized soil. Whereas at low fertility soil biota had net neutral to positive effects on plant community biomass but the beneficial effects did not increase with increasing plant species richness. Instead, soil biota neutrally affected the positive plant species richness–community biomass relationship, presumably due to non-specific effects of beneficial soil biota. 5. Synthesis. Soil biota and soil fertility interactively determine plant species richness–community biomass relationships. Moreover, soil biota modulate the complementary resource use among plant species. These findings suggest that environmental context plays an important role in determining whether and how soil biota generate the biodiversity–productivity relationship. Future studies would benefit from revealing the mechanisms underlying the interactive effects of soil biota, soil fertility, and plant diversity on ecosystem functioning.1. 植物群落生产力通常随植物多样性提升而增加，该现象可通过两种机制解释：一是植物物种间的资源利用互补性（complementarity effect，互补效应），二是高多样性植物群落中优势高产物种的筛选效应（selection effect，选择效应）。近期研究还发现，土壤生物群（soil biota）可通过对低多样性植物群落的生产力抑制程度高于高多样性群落，从而强化植物多样性-生产力的正相关关系。但目前仍不清楚土壤肥力是否会参与调控土壤生物群对植物多样性-生产力关系的作用路径。 2. 本研究提出如下假说：在高土壤肥力条件下，土壤生物群的负效应占主导，其对植物单播群落生物量的抑制作用强于高多样性植物群落；反之，在低土壤肥力条件下，土壤生物群的正效应占主导，可促进植物的资源分区利用，并提升高多样性植物群落的群落级生物量。据此我们预期，无论土壤肥力高低，植物多样性与群落生产力均呈正相关关系，但二者的驱动机制存在差异。 3. 本研究以木本幼苗为实验材料，构建了包含4个物种丰富度梯度（1、2、4、8个物种）的植物组合群落，并在两种养分水平（低肥力与高肥力）的灭菌与未灭菌（灭菌土壤+活体土壤接种物）土壤中开展种植实验。 4. 实验结果显示：在高肥力条件下，土壤生物群的负效应占主导，其对高多样性植物群落的生物量抑制作用强于单播群落，进而导致高多样性植物群落的互补效应下降，且未灭菌土壤中植物物种丰富度与群落生物量间的相关性无统计学显著性。而在低肥力条件下，土壤生物群对植物群落生物量的净效应呈中性至正相关，但这种有益效应并未随植物物种丰富度提升而增强。相反，土壤生物群对植物物种丰富度-群落生物量的正相关关系仅产生中性影响，这可能源于有益土壤生物群的非特异性作用。 5. 综合分析：土壤生物群与土壤肥力共同调控植物物种丰富度-群落生物量的关系。此外，土壤生物群可调控植物物种间的互补资源利用模式。上述结果表明，环境背景在决定土壤生物群能否以及如何形成生物多样性-生产力关系中发挥关键作用。未来研究若能阐明土壤生物群、土壤肥力与植物多样性的交互效应对生态系统功能的内在调控机制，将进一步推动该领域的研究进展。