Mutualism theory predicts how legumes influence biodiversity-ecosystem function relationships under global change

初级生产力，即通过光合作用将太阳能转化为植物生物量，是一项特别重要的生态系统服务，支持大多数全球生态系统，并与植物生物多样性呈正相关。该项目将增加对生物多样性-生产力关系的机械性理解，以更好地解释环境条件如何影响生态系统服务。生态学理论预测，植物物种之间的差异是生物多样性-生产力关系变化的基础。然而，植物物种之间这种差异背后的机制很少被实验量化，使得植物差异和生物多样性-生产力关系之间的因果关系难以捉摸。豆科植物被称为根瘤菌的有益土壤细菌感染，根瘤菌固定大气中的氮(N)，以换取植物寄主的碳(C)。由于大多数植物从土壤中获取氮素，通过这种互惠关系获得大气氮素可以区分豆科植物和非豆科植物，从而影响生产力-多样性关系。该项目将对区分豆类物种和非豆类物种的生物过程进行实验研究，以了解这些差异是如何导致美国明尼苏达州长期生物多样性、二氧化碳和氮素操纵实验--Biocon--的初级生产力模式发生变化的。为了促进公众对科学的理解，中学生将在两个N处理下种植和观察接种了当地细菌的豆类种子，以测试来自高土壤N地区的细菌是否比来自低土壤N地区的细菌更有益。本科生将接受相关技术培训，并在本工作范围内开发独立的项目。研究和推广项目将为当前和未来全球变化情景下的生态系统功能管理提供信息，对人类福祉具有重要影响。豆科物种之间的生态位差异(ND)和相对适合度差异(RFD)将通过确定周围条件下Biocon生物多样性地块土壤样本中特定物种根瘤菌群落(NRC)的组成和密度以及植物受益来评估。结构方程模型将ND和RFD及其潜在机制与每个多样性处理计算的相对产量总和联系起来，以检验豆类和非豆类之间较高的ND会产生更强的丰富度-生产力关系，而较高的RFD会削弱丰富度-生产力关系。将通过确定每个生物多样性、CO2和N处理组合的NRC的组成和密度及其植物效益，来评估NRC对CO2和/或N增加的响应的演变及其对丰富度-生产力关系的影响。最后，将通过混合接种实验检验不同豆科植物在二氧化碳和/或氮的有效性如何改变根瘤菌合作的实施(伙伴选择和制裁)方面的差异，以及这种差异对丰富度-生产力关系的影响。

Primary productivity, the conversion of solar energy to plant biomass via photosynthesis, is a particularly important ecosystem service that supports most global ecosystems and is positively related to plant biodiversity. This project will increase mechanistic understanding of the biodiversity-productivity relationship to better explain how environmental conditions influence ecosystem services. Ecological theory predicts that differences among plant species underlie variation in the biodiversity-productivity relationship. However, the mechanisms underlying this variation among plant species are rarely experimentally quantified, leaving causal connections between plant variation and the biodiversity-productivity relationship elusive. Plants in the legume (bean) family are infected by beneficial soil bacteria called rhizobia, which fix atmospheric nitrogen (N) in exchange for carbon (C) from their plant hosts. As most plants obtain N from soil, access to atmospheric N via this mutualism can differentiate legumes from non-legumes, thus influencing the productivity-diversity relationship. This project will experimentally examine biotic processes that differentiate legume species from each other and from non-legumes to understand how these differences cause variation in patterns of primary productivity within a long-term biodiversity, CO2, and N manipulation experiment in Minnesota, USA--BioCON. To promote public understanding of science, middle school students will grow and observe legume seeds inoculated with local bacteria under two N treatments to test if bacteria from regions with high soil N are less beneficial than those from regions with low soil N. Undergraduates will be trained in relevant techniques and develop independent projects within the scope of this work. The research and outreach projects will inform management of ecosystem function under current and future global change scenarios, with important implications for human well-being.Niche differences (ND) and relative fitness differences (RFD) among legume species will be assessed by determining the composition and density of, and plant benefit from, the species-specific nodulating rhizobial community (NRC) in soil samples from the ambient condition BioCON biodiversity plots. Structural equation models will relate ND and RFD, and their underlying mechanisms, to relative yield totals calculated from each diversity treatment, to test the hypothesis that higher ND between legumes and non-legumes produces stronger richness-productivity relationships and higher RFD weakens the richness-productivity relationship. Evolution of the NRC in response to enhanced CO2 and/or N, and its consequences for the richness-productivity relationship, will be assessed by determining the composition and density of, and plant benefit derived from, the NRC of each BioCON diversity, CO2, and N treatment combination. Finally, variation among legume species in how CO2- and/or N-availability shifts enforcement of rhizobial cooperation (partner choice and sanctions), and the consequences of this variation for the richness-productivity relationship, will be examined through mixed-inoculation experiments.