Data and code corresponding to: Contemporary evolution rivals the effects of rhizobium abundance on soil nitrogen availability in experimental mesocosms

Because genotypes within a species commonly differ in traits that influence other species, whole communities, or even ecosystem functions, evolutionary change within one key species may affect community and ecosystem processes. Here we use experimental mesocosms to test how the evolution of reduced cooperation in rhizobium mutualists in response to 20 years of nitrogen fertilization compares to the effects of rhizobium abundance on soil nitrogen availability and plant community composition and diversity. The evolution of reduced rhizobium cooperation caused reductions in soil nitrogen that were as strong, or even stronger, than substantially reducing rhizobium mutualist abundance in a community. Effects of both rhizobium evolution and rhizobium inoculation on legume dominance, plant community composition, and plant species diversity were much smaller in magnitude, but suggest that rhizobium evolution can alter the relative abundance of plant functional groups. Our findings indicate that the consequences of rapid microbial evolution for ecosystems and communities can rival the effects resulting from the presence or abundance of keystone mutualists.

Methods
We conducted a greenhouse experiment manipulating rhizobium evolutionary history (rhizobia isolated from long-term nitrogen addition treatments or adajacent control plots) and rhizobium abundance (uninoculated) on experimental mesocosms simulating early successional plant communities. Data was originally collected on hard copy datasheets, was entered into spreadsheets, and proofed for errors. A number of values in the accompanying data files are calculations based on raw data (e.g., diversity indices), but the data has not otherwise been modified.

由于同一物种内的不同基因型通常携带可影响其他物种、整个群落乃至生态系统功能的性状，因此单一关键物种内的演化改变可能会对群落与生态系统过程产生影响。本研究借助实验中型生态系统（mesocosms），旨在对比两类效应的差异：一是针对20年氮肥施用演化出合作能力减弱的根瘤菌共生体（rhizobium mutualists）的演化效应，二是根瘤菌丰度对土壤氮有效性、植物群落组成及物种多样性的影响。

根瘤菌合作能力减弱的演化所引发的土壤氮含量降低效应，其强度可与群落中大幅降低根瘤菌共生体丰度所带来的效应相当，甚至更强。根瘤菌演化与根瘤菌接种对豆科植物优势度、植物群落组成及植物物种多样性的影响幅度均相对较小，但结果表明根瘤菌演化能够改变植物功能群的相对丰度。本研究结果显示，微生物快速演化对生态系统与群落造成的影响，可与关键共生体（keystone mutualists）的存在或丰度变化所带来的效应相媲美。

方法
本研究开展温室实验，设置根瘤菌演化历史（从长期氮肥添加样地或邻近对照样地分离得到的根瘤菌）与根瘤菌丰度（含未接种处理）两个操控变量，实验中型生态系统模拟了早期演替的植物群落。原始数据最初记录于纸质数据表，随后录入电子表格并经过错误核查。配套数据文件中的部分数值由原始数据计算得到（如多样性指数），未进行其他额外修改。