Data from: Functional group, biomass, and climate change effects on ecological drought in semiarid grasslands

Water relations in plant communities are influenced both by contrasting functional groups (grasses, shrubs) and by climate change via complex effects on interception, uptake and transpiration. We modelled the effects of functional group replacement and biomass increase, both of which can be outcomes of invasion and vegetation management, and climate change on ecological drought (soil water potential below which photosynthesis stops) in 340 semiarid grassland sites over 30-year periods. Relative to control vegetation (climate and site-determined mixes of functional groups), the frequency and duration of drought were increased by shrubs and decreased by annual grasses. The rankings of shrubs, control vegetation, and annual grasses in terms of drought effects were generally consistent in current and future climates, suggesting that current differences among functional groups on drought effects predict future differences. Climate change accompanied by experimentally-increased biomass (i.e. the effects of invasions that increase community biomass, or management that increases productivity through fertilization or respite from grazing) increased drought frequency and duration, and advanced drought onset. Our results suggest that the replacement of perennial temperate semiarid grasslands by shrubs, or increased biomass, can increase ecological drought both in current and future climates.

植物群落的水分关系同时受两类因素调控：一是不同功能群（草本、灌木）的特征差异，二是气候变化——后者通过对冠层截留、水分吸收与蒸腾作用的复杂效应施加影响。本研究针对340个半干旱草原样地开展了为期30年的模型模拟，探究功能群更替、生物量提升（二者均可由生物入侵与植被管理引发）以及气候变化对生态干旱（即光合作用停止时的土壤水势阈值）的影响。相较于由气候与样地特征决定的功能群混合对照植被，灌木会提升干旱发生频率与持续时长，而一年生草本则会降低二者。灌木、对照植被与一年生草本的干旱效应排序在当前与未来气候情景下整体保持一致，表明当前功能群间的干旱效应差异可用于预测未来的效应差异。当气候变化伴随实验性生物量提升（即通过提升群落生物量的生物入侵，或通过施肥、休牧等管理手段提升群落生产力所引发的效应）时，干旱发生频率、持续时长均会增加，且干旱起始时间会提前。本研究结果表明，无论是以灌木取代温带半干旱多年生草原群落，还是提升群落生物量，均可在当前与未来气候情景下加剧生态干旱。