Data from: Atmospheric N deposition alters co-occurrence, but not functional potential among saprotrophic bacterial communities

The use of co-occurrence patterns to investigate interactions between microorganisms has provided novel insight into organismal interactions within microbial communities. However, anthropogenic impacts on microbial co-occurrence patterns and ecosystem function remain an important gap in our ecological knowledge. In a northern hardwood forest ecosystem located in Michigan, USA, twenty years of experimentally increased atmospheric N deposition has reduced forest floor decay and increased soil C storage. This ecosystem-level response occurred concomitantly with compositional changes in saprophytic fungi and bacteria. Here, we investigated the influence of experimental N deposition on biotic interactions among forest floor bacterial assemblages by employing phylogenetic and molecular ecological network analysis. When compared to the ambient treatment, the forest floor bacterial community under experimental N deposition was less rich, more phylogenetically dispersed, and exhibited a more clustered co-occurrence network topology. Together, our observations reveal the presence of increased biotic interactions among saprotrophic bacterial assemblages under future rates of N deposition. Moreover, they support the hypothesis that nearly two decades of experimental N deposition can modify the organization of microbial communities and provide further insight into why anthropogenic N deposition has reduced decomposition, increased soil C storage, and accelerated phenolic DOC production in our field experiment.

利用共现模式（co-occurrence patterns）探究微生物间的相互作用，可为解析微生物群落（microbial communities）内的物种互作关系提供全新视角。然而，人为活动对微生物共现模式与生态系统功能的影响，仍是当前生态学认知中尚未填补的重要空白。在美国密歇根州的一处北方硬木林生态系统中，为期20年的模拟大气氮沉降（atmospheric N deposition）增施实验，已显著降低了地表枯落物分解（forest floor decay）速率，并提升了土壤碳储量（soil C storage）。这一生态系统尺度的响应，与腐生真菌（saprophytic fungi）和细菌的群落组成变化同步发生。本研究借助系统发育分析（phylogenetic analysis）与分子生态网络分析（molecular ecological network analysis）手段，探究了模拟氮沉降实验对地表细菌群落间生物互作关系的影响。结果显示，与自然氮沉降对照处理（ambient treatment）相比，模拟增氮处理下的地表细菌群落物种丰富度更低，系统发育离散程度更高，且共现网络拓扑结构更呈聚集模式。综合来看，本研究结果揭示：在未来氮沉降速率情境下，腐生细菌群落（saprotrophic bacterial assemblages）间的生物互作强度有所提升。此外，该结果验证了"近20年的模拟氮沉降实验可改变微生物群落组织模式"这一假说，同时也为阐释本野外实验中人为氮沉降为何会降低枯落物分解速率、提升土壤碳储量并加速酚类溶解性有机碳（Dissolved Organic Carbon, DOC）生成，提供了进一步的生态学见解。