Two hypotheses have been used to explain the loss of plant diversity with nutrient addition. The nutrient identity hypothesis posits that biodiversity loss is due to a specific limiting nutrient, such as nitrogen (N) or phosphorus (P), while the niche dimension hypothesis posits that adding a larger number of limiting nutrients, regardless of their identity, results in biodiversity loss. These two hypotheses have not previously been tested together simultaneously. Here, we conduct that analysis to enable their relative effect sizes to be compared. We manipulated the supply of eight nutrients in the same experimental meadow grassland site to isolate the effects of the identity of added nutrients versus the number of added nutrients on biodiversity loss. We found support for both hypotheses, with the largest negative effects on biodiversity measures being due to N, or N and P treatment, with additional more minor effects of the number of added nutrients. Structural equation models (SEMs) suggested both identity and number of added nutrients had direct negative effects on biodiversity, likely caused by species' innate ability to competitively respond to nutrients, especially in response to disease, herbivory, and stress. SEMs also suggested indirect effects arising from nutrient‐driven increases in aboveground biomass, which resulted in intensified competition for light and the competitive exclusion of short‐statured species. These effects were exacerbated by the nutrients N and P which caused a shift in biomass accumulation from belowground to aboveground. The results highlight that a multi‐nutrient perspective will improve our ability to effectively manage, monitor, and restore ecosystems.

中文翻译：

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养分对植物多样性丧失的影响源于养分身份和生态位维度的减少


有两种假设被用来解释营养添加导致植物多样性的丧失。营养物质同一性假说假设生物多样性丧失是由于特定的限制性营养物质，如氮 （N） 或磷 （P），而生态位维度假说假设添加大量限制性营养物质，无论它们的身份如何，都会导致生物多样性丧失。这两个假设以前没有同时一起测试过。在这里，我们进行该分析以比较它们的相对效应大小。我们操纵了同一实验草甸草原场地中 8 种养分的供应，以分离添加养分的身份与添加养分数量对生物多样性丧失的影响。我们发现这两种假设都得到了支持，对生物多样性措施的最大负面影响是由于 N 或 N 和 P 处理，以及添加营养物质数量的额外更轻微的影响。结构方程模型 （SEMs） 表明，添加的营养物质的身份和数量都对生物多样性有直接的负面影响，这可能是由于物种天生对营养物质的竞争反应能力造成的，尤其是在应对疾病、食草和压力时。SEM 还表明，营养驱动的地上生物量增加会产生间接影响，这导致了对光的竞争加剧和对矮个子物种的竞争排斥。营养物质 N 和 P 加剧了这些影响，导致生物量积累从地下转移到地上。结果强调，多营养视角将提高我们有效管理、监测和恢复生态系统的能力。