Higher species richness enhances yield stability in intensively managed grasslands with experimental disturbance

Climate models predict increased frequency and severity of drought events. At an Irish and Swiss site, experimental summer droughts were applied over two successive years to grassland plots sown with one, two or four grassland species with contrasting functional traits. Mean yield and plot-to-plot variance of yield were measured across harvests during drought and after a subsequent post-drought recovery period. At both sites, there was a positive relationship between species richness and yield. Under rainfed control conditions, mean yields of four-species communities were 32% (Wexford, Ireland) and 51% (Zürich, Switzerland) higher than in monocultures. This positive relationship was also evident under drought, despite significant average yield reductions (-27% at Wexford; -21% at Zürich). Four-species communities had lower plot-to-plot variance of yield compared to monoculture or two-species communities under both rainfed and drought conditions, which demonstrates higher yield stability in four-species communities. At the Swiss but not the Irish site, a high degree of species asynchrony could be identified as a mechanism underlying increased temporal stability in four-species communities. These results indicate the high potential of multi-species grasslands as an adaptation strategy against drought events and help achieve sustainable intensification under both unperturbed and perturbed environmental conditions.

气候模型预测，干旱事件的发生频率与严重程度均将上升。在爱尔兰与瑞士的两处试验站点，研究人员连续两年对夏季草地开展干旱胁迫试验，试验地块分别播种了功能性状存在显著差异的1种、2种或4种草地植物物种。于干旱胁迫期间及后续干旱恢复阶段的多次收割中，测定了地块的平均产量与地块间产量方差。两处站点均观测到物种丰富度与产量呈正相关关系。在雨养对照条件下，4物种群落的平均产量较单物种群落分别高出32%（爱尔兰韦克斯福德站点）与51%（瑞士苏黎世站点）。尽管干旱胁迫导致平均产量显著下降（韦克斯福德站点降幅27%，苏黎世站点降幅21%），但该正相关关系在干旱胁迫下依然显著。在雨养与干旱胁迫两种条件下，4物种群落的地块间产量方差均低于单物种或2物种群落，表明4物种群落的产量稳定性更高。仅在瑞士站点，物种间高度的异步性可被认定为4物种群落时间稳定性提升的内在机制，爱尔兰站点未观测到该现象。本研究结果表明，多物种草地可作为应对干旱事件的有效适应策略，同时有助于在自然与受干扰的环境条件下实现可持续集约化生产。