Differences in species' abilities to capture resources can drive competitive hierarchies, successional dynamics, community diversity, and invasions. To investigate mechanisms of resource competition within a nitrogen (N) limited California grassland community, we established a manipulative experiment using an R* framework. R* theory holds that better competitors within a N limited community should better depress available N in monoculture plots and obtain higher abundance in mixture plots. We asked whether (1) plant uptake or (2) plant species influences on microbial dynamics were the primary drivers of available soil N levels in this system where N structures plant communities. To disentangle the relative roles of plant uptake and microbially-mediated processes in resource competition, we quantified soil N dynamics as well as N pools in plant and microbial biomass in monoculture plots of 11 native or exotic annual grassland plants over one growing season. We found a negative correlation between plant N content and soil dissolved inorganic nitrogen (DIN, our measure of R*), suggesting that plant uptake drives R*. In contrast, we found no relationship between microbial biomass N or potential net N mineralization and DIN. We conclude that while plant-microbial interactions may have altered the overall quantity of N that plants take up, the relationship between species' abundance and available N in monoculture was largely driven by plant N uptake in this first year of growth.
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机译:物种捕获资源能力的差异可能会导致竞争等级制度,演替动态,社区多样性和入侵。为了调查氮(N)有限的加利福尼亚草原社区内资源竞争的机制,我们建立了使用R *框架的操纵性实验。 R *理论认为,在一个氮有限的社区中,更好的竞争者应该更好地抑制单一耕作地中的可用氮,并在混合地中获得更高的丰度。我们询问(1)植物吸收或(2)植物种类对微生物动力学的影响是否是该系统中N构成植物群落的土壤N水平的主要驱动因素。为了弄清植物吸收和微生物介导的过程在资源竞争中的相对作用,我们在一个生长季节内,对11种本地或外来一年生草地植物的单一耕作地中的土壤氮动态以及植物和微生物生物量中的氮库进行了定量。我们发现植物氮含量与土壤溶解的无机氮(DIN,我们对R *的测量值)之间呈负相关,表明植物吸收驱动R *。相反,我们发现微生物生物量氮或潜在的净氮矿化与DIN之间没有关系。我们得出的结论是,虽然植物与微生物之间的相互作用可能改变了植物吸收的氮的总量,但单种养殖中物种丰度与有效氮之间的关系在很大程度上取决于生长第一年中植物对氮的吸收。
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