Abstract Global nitrogen (N) deposition generally reduces plant biodiversity and changes ecosystem carbon (C) cycle. Light limitation caused by accumulated litter under N enrichment is proposed as a main reason for the decreases of biodiversity and ecosystem C sequestration. However, mechanisms underlying this light limitation effect are not well understood, especially under different N input rates. We conducted a field manipulation experiment with N addition as the primary factor nested with litter manipulation as the secondary factor in an alpine meadow in 2017, measured ecosystem C fluxes and investigated the plant communities about 10 days after the N addition treatment, to examine the responses of biodiversity and ecosystem C sequestration to litter manipulation and N addition. Our results showed that alleviation of light limitation by removing litter increased plant species richness under N enrichment, which principally caused by higher species gains and lower losses. Common and rare species contributed most of the increased species as light limitation was relieved. N addition had no significant impact on net ecosystem productivity (NEP), whereas alleviation of light limitation and the subsequent increase in plant coverage and density under N enrichment stimulated gross primary productivity (GPP) but did not affect ecosystem respiration (ER), causing positive responses of NEP. This study highlights the promoting effect of the enhanced light availability through litter removal on species diversity and ecosystem C sequestration under N enrichment. These findings provide new insights into the mechanisms underlying light limitation influence on biodiversity and ecosystem C sequestration under N enrichment. We suggest that grassland management by removing the accumulated litter is an adaptive way to enhance light availability, mitigate diversity loss and thus increase C sequestration under eutrophication.

中文翻译：

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在高寒草甸富氮条件下减轻光照限制增加植物多样性和生态系统碳固存

摘要 全球氮 (N) 沉积通常会降低植物生物多样性并改变生态系统碳 (C) 循环。建议在富氮下累积凋落物引起的光照限制是生物多样性和生态系统碳固存减少的主要原因。然而，这种光限制效应的潜在机制尚不清楚，尤其是在不同的 N 输入速率下。我们于 2017 年在高寒草甸进行了以施氮为主要因素，以凋落物处理为次要因素的田间操纵实验，测量了生态系统 C 通量并调查了施氮处理后约 10 天的植物群落，以检查响应生物多样性和生态系统 C 封存对垃圾处理和 N 添加的影响。我们的结果表明，通过去除凋落物来减轻光限制增加了 N 富集下的植物物种丰富度，这主要是由更高的物种增益和更低的损失引起的。随着光照限制的缓解，常见和稀有物种贡献了大部分增加的物种。N添加对净生态系统生产力（NEP）没有显着影响，而光照限制的减轻以及随后在N富集下植物覆盖度和密度的增加刺激了总初级生产力（GPP）但不影响生态系统呼吸（ER），导致积极NEP 的回应。本研究强调了通过凋落物去除来增强光照对物种多样性和 N 富集下生态系统碳封存的促进作用。这些发现提供了对光限制影响 N 富集下生物多样性和生态系统 C 固存的潜在机制的新见解。我们建议通过清除堆积的凋落物来管理草地是一种适应性方法，可以提高光照可用性，减轻多样性损失，从而增加富营养化下的 C 封存。