Data from: Mowing exacerbates the loss of ecosystem stability under nitrogen enrichment in a temperate grassland

Summary: 1. Global reactive nitrogen (N) is projected to further increase in the coming years. Previous studies have demonstrated that N enrichment weakens the temporal stability of ecosystem primary productivity through decreased biodiversity and species asynchrony. Mowing is a globally common practice in grasslands; and infrequent mowing can maintain or increase plant diversity under N enrichment conditions. However, it is unclear how infrequent mowing affects ecosystem stability in the face of N enrichment. 2. By independently manipulating the frequency (twice vs. monthly additions yr–1) and rate (i.e., 0, 1, 2, 3, 5, 10, 15, 20, and 50 g N m–2 yr–1) of NH4NO3 inputs and mowing (unmown vs. mown) over three years (2011–2013) in a temperate grassland of northern China, we aimed to examine the interactive effects of N enrichment and mowing on ecosystem stability. 3. The results show that mowing maintained a positive relationship between species richness and ecosystem stability despite N addition but that it exacerbated the negative effects of N addition on ecosystem stability. Mowing increased mean primary productivity and plant species richness, but it also increased the synchrony of population fluctuations and the variability of primary productivity under N enrichment, thereby contributing to a decline in ecosystem stability. 4. Thus, our study reveals that infrequent mowing can buffer the negative effects of N enrichment on biodiversity to some extent and further increase primary productivity but it exacerbates the loss of ecosystem stability with N enrichment, thereby threatening local and/or semiarid regional food security.研究摘要： 1. 全球活性氮（reactive nitrogen）预计未来数年将持续增长。既往研究表明，氮富集（N enrichment）可通过降低生物多样性与物种异步性（species asynchrony），削弱生态系统初级生产力的时间稳定性。刈割（mowing）是全球草原普遍采用的管理措施，在氮富集条件下，低频刈割可维持甚至提升植物多样性，但目前尚不清楚在氮富集背景下，低频刈割如何影响生态系统稳定性。 2. 本研究于中国北方温带草原（temperate grassland）开展了2011-2013年为期3年的野外控制实验，通过独立设置硝酸铵（NH4NO3）的施入频率（每年2次与每月1次）、施入速率（0、1、2、3、5、10、15、20、50克氮·平方米⁻¹·年⁻¹）以及刈割处理（不刈割与刈割），旨在探究氮富集与刈割的交互作用对生态系统稳定性的影响。 3. 研究结果显示，尽管存在施氮处理，刈割仍维持了物种丰富度与生态系统稳定性之间的正相关关系，但同时加剧了施氮对生态系统稳定性的负面影响。刈割提升了平均初级生产力与植物物种丰富度，但在氮富集条件下，也增大了种群波动同步性与初级生产力变异性，最终导致生态系统稳定性下降。 4. 综上，本研究表明，低频刈割可在一定程度上缓解氮富集对生物多样性的负面影响，并进一步提升初级生产力，但同时会加剧氮富集背景下生态系统稳定性的丧失，进而威胁本地乃至半干旱区域的粮食安全。