Teasing apart plant community responses to N enrichment: the roles of resource limitation, competition and soil microbes

Although ecologists have documented the effects of nitrogen enrichment on productivity, diversity and species composition, we know little about the relative importance of the mechanisms driving these effects. We propose that distinct aspects of environmental change associated with N enrichment (resource limitation, asymmetric competition, and interactions with soil microbes) drive different aspects of plant response. We test this in greenhouse mesocosms, experimentally manipulating each factor across three ecosystems: tallgrass prairie, alpine tundra and desert grassland. We found that resource limitation controlled productivity responses to N enrichment in all systems. Asymmetric competition was responsible for diversity declines in two systems. Plant community composition was impacted by both asymmetric competition and altered soil microbes, with some contributions from resource limitation. Results suggest there may be generality in the mechanisms of plant community change with N enri...尽管生态学家已探明氮富集对植物生产力、多样性及物种组成的影响，但我们对驱动这些效应的各类机制的相对重要性仍知之甚少。本研究提出，与氮富集相关的环境变化的不同维度（资源限制、不对称竞争及与土壤微生物的互作）分别调控植物响应的不同方面。我们在温室中型实验生态系统（mesocosms）中对该假说进行验证，在高草草原、高山苔原与荒漠草原三类生态系统中对各因子开展实验调控。研究发现，在所有研究系统中，资源限制均主导了植物生产力对氮富集的响应。不对称竞争则是两类系统中植物多样性下降的诱因。植物群落组成同时受到不对称竞争与土壤微生物群落改变的影响，资源限制也起到了一定作用。研究结果表明，氮富集驱动植物群落变化的机制或存在普遍性