Vitra Amarante, Deléglise Claire, Meisser Marco, Risch Anita C, Signarbieux Constant, Lamacque Lia, Delzon Sylvain, Buttler Alexandre, Mariotte Pierre
Ecole Polytechnique Fédérale de Lausanne (EPFL), School of Architecture, Civil and Environmental Engineering (ENAC), Laboratory of Ecological Systems (ECOS), Switzerland.
Swiss Federal Institute for Forest, Snow and Landscape Research (WSL), Site Lausanne, Lausanne, Switzerland.
AoB Plants. 2019 Apr 4;11(3):plz023. doi: 10.1093/aobpla/plz023. eCollection 2019 Jun.
Drought can occur at different times during the grassland growing season, likely having contrasting effects on forage production when happening early or later in the season. However, knowledge about the interacting effects of the timing of drought and the development stage of the vegetation during the growing season is still scarce, thus limiting our ability to accurately predict forage quantity losses. To investigate plant community responses to drought seasonality (early- vs. late-season), we established a drought experiment in two permanent grasslands of the Swiss Jura Mountains that are used for forage production. We measured three plant functional traits, including two leaf traits related to plant economics (specific leaf area, SLA; leaf dry matter content, LDMC) and one hydraulic trait related to physiological function (predicted percentage loss of hydraulic conductance, PLCp), of the most abundant species, and plant above-ground biomass production. Plant species composition was also determined to calculate community-weighted mean (CWM) traits. First, we observed that CWM trait values strongly varied during the growing season. Second, we found that late-season drought had stronger effects on CWM trait values than early-season drought and that the plant hydraulic trait was the most variable functional trait. Using a structural equation model, we also showed that reduction in soil moisture had no direct impacts on above-ground biomass production. Instead, we observed that the drought-induced decrease in above-ground biomass production was mediated by a higher CWM PLCp (i.e. higher risk of hydraulic failure) and lower CWM SLA under drought. Change in CWM SLA in response to drought was the best predictor of community above-ground biomass production. Our findings reveal the importance of drought timing together with the plant trait responses to assess drought impacts on grassland biomass production and suggest that incorporating these factors into mechanistic models could considerably improve predictions of climate change impacts.
干旱可能发生在草原生长季节的不同时间，在季节早期或晚期发生时，可能对牧草产量产生截然不同的影响。然而，关于干旱发生时间与生长季节植被发育阶段的相互作用影响的知识仍然匮乏，从而限制了我们准确预测牧草数量损失的能力。为了研究植物群落对干旱季节性（季节早期与晚期）的响应，我们在瑞士汝拉山脉两个用于牧草生产的永久草地上开展了一项干旱实验。我们测量了最优势物种的三个植物功能性状，包括两个与植物经济学相关的叶片性状（比叶面积，SLA；叶片干物质含量，LDMC）和一个与生理功能相关的水力性状（预测的水力导度损失百分比，PLCp），以及植物地上生物量产量。还确定了植物物种组成以计算群落加权平均（CWM）性状。首先，我们观察到CWM性状值在生长季节中变化很大。其次，我们发现季节晚期干旱对CWM性状值的影响比季节早期干旱更强，并且植物水力性状是最具变化性的功能性状。使用结构方程模型，我们还表明土壤水分减少对地上生物量产量没有直接影响。相反，我们观察到干旱导致的地上生物量产量下降是由干旱条件下更高的CWM PLCp（即更高的水力故障风险）和更低的CWM SLA介导的。CWM SLA对干旱的响应变化是群落地上生物量产量的最佳预测指标。我们的研究结果揭示了干旱发生时间以及植物性状响应对于评估干旱对草地生物量生产影响的重要性，并表明将这些因素纳入机理模型可以显著改善对气候变化影响的预测。
