Abstract：
The primary mechanisms contributing to nitrogen (N) addition induced grassland biodiversity loss, namely light competition and soil cation toxicity, are often examined separately in various studies. However, their relative significance in governing biodiversity loss along N addition gradient remains unclear. We conducted a 4-yr field experiment with five N addition rates (0, 2, 10, 20, and 50 g N m-2 yr-1) and performed a meta-analysis using global data from 239 observations in N-fertilized grassland ecosystems. Results from our field experiment and meta-analysis indicate that both light competition and soil cation (e.g. Mn2+ and Al3+) toxicity contribute to plant diversity loss under N enrichment. The relative importance of these mechanisms varied with N enrichment intensity. Light competition played a more significant role in influencing species richness under low N addition (≤ 10 g m-2 yr-1), while cation toxicity became increasingly dominant in reducing biodiversity under high N addition (>10 g m-2 yr-1). Therefore, a transition from light competition to cation toxicity occurs with increasing N availability. These findings imply that the biodiversity loss along the N gradient is regulated by distinct mechanisms, necessitating the adoption of differential management strategies to mitigate diversity loss under varying intensities of N enrichment.
摘要：
导致氮（N）添加导致草地生物多样性丧失的主要机制，即光竞争和土壤阳离子毒性，通常在各种研究中单独检查。然而,它们在控制沿N添加梯度的生物多样性损失中的相对意义尚不清楚。我们进行了为期4年的田间试验，采用5种氮添加率（0、2、10、20和50gNm-2yr-1），并使用来自239个氮的观测值的全球数据进行了荟萃分析。施肥的草地生态系统。我们的田间试验和荟萃分析的结果表明，光照竞争和土壤阳离子（例如Mn2和Al3）毒性都会导致氮富集下植物多样性的丧失。这些机制的相对重要性随N富集强度而变化。在低氮添加（≤10gm-2yr-1）下，光竞争在影响物种丰富度方面发挥了更重要的作用，而在高氮添加(>10gm-2yr-1)下，阳离子毒性在减少生物多样性方面越来越占主导地位。因此,随着氮利用率的增加，发生了从光竞争到阳离子毒性的转变。这些发现表明，沿着氮梯度的生物多样性损失是由不同的机制调节的，在不同的氮富集强度下，必须采用不同的管理策略来减轻多样性损失。
