Recurrent drought amplifies drought impacts and increases seasonal synchrony in mountain grassland communities

Climate change increases the frequency and severity of drought events with strong repercussions on grassland ecosystems. While the effects of single drought events on ecosystem structure and functioning are well understood, it is largely unknown whether and how drought frequency modifies ecosystem responses to drought. Here, we assessed how the increase in frequency of severe, annual summer drought impacted grassland communities. We examined these effects in a species-rich sub-alpine mountain meadow with drought frequencies of one, three, and 13 years, compared to ambient conditions. We found that high drought frequency increased seasonal plant community synchrony. This pattern was associated with a reduction in species richness, a shift in plant functional groups, a loss of early-seasonal plant species, and a constrained establishment of seedlings throughout the growing season. Additionally, these changes were accompanied by a decreased fraction of biomass as drought frequency increase..., , , # Data from: Recurrent drought amplifies drought impacts and increases seasonal synchrony in mountain grassland communities [https://doi.org/10.5061/dryad.4tmpg4fmt](https://doi.org/10.5061/dryad.4tmpg4fmt) ## Description of the data and file structure Four summer drought treatments were established in the enclosed area at the study site: a single year summer drought, three years of recurrent summer drought, 13 years of recurrent summer drought, and ambient conditions (n = 4, respectively). In total, 4 plots for ambient, single, three, and 13 years of drought frequency were installed four weeks before summer drought simulation in 2020, respectively. In all 16 plots, species composition and vegetation height (cm) were measured every two weeks from 22 May to 22 October 2020. Plant species composition was estimated by noting for each species present the number of modules and flowering stems. Seedling composition in the plots was counted separately every three weeks between the 23 June a...,气候变化提升了干旱事件的发生频次与严重程度，对草原生态系统造成强烈的连锁影响。尽管单次干旱事件对生态系统结构与功能的影响已得到充分阐明，但干旱频次如何改变生态系统对干旱的响应，以及该响应是否存在，目前仍不明确。本研究旨在探究年度夏季重度干旱的频次增加如何影响草原群落。我们在物种丰富的亚高山草甸（sub-alpine mountain meadow）中设置了1年、3年、13年的干旱频次梯度，并以自然背景条件为对照，以此检验上述效应。 研究结果显示，高干旱频次提升了植物群落的季节同步性（seasonal synchrony）。该现象与物种丰富度下降、植物功能群（plant functional groups）组成偏移、早春植物物种丧失，以及整个生长季幼苗定植受抑制密切相关。此外，随着干旱频次增加，生物量占比亦呈下降趋势…… # 数据来源：《周期性干旱加剧山地草原群落的干旱影响并提升其季节同步性》 [https://doi.org/10.5061/dryad.4tmpg4fmt](https://doi.org/10.5061/dryad.4tmpg4fmt) ## 数据与文件结构说明 研究样地的封闭区域内设置了4组夏季干旱处理：1年单次夏季干旱、3年周期性夏季干旱、13年周期性夏季干旱，以及自然对照（每组重复数n=4）。2020年夏季干旱模拟实验开展前4周，分别完成了自然对照、1年、3年、13年干旱频次处理的共16个样地的布设。2020年5月22日至10月22日期间，每两周对全部16个样地的物种组成与植被高度（单位：厘米）进行测定。植物物种组成通过记录样地内各物种的分株数与开花茎秆数进行估算。样地内的幼苗组成则于6月23日起每三周单独计数一次……