Department of Environmental Science and Policy, University of California, Davis, CA 95616;
Department of Plant Sciences, University of California, Davis, CA 95616.
Proc Natl Acad Sci U S A. 2019 Mar 19;116(12):5576-5581. doi: 10.1073/pnas.1818543116. Epub 2019 Mar 4.
Trait-based approaches are increasingly used to predict ecological consequences of climate change, yet seldom have solid links been established between plant traits and observed climate-driven community changes. Most analyses have focused on aboveground adult plant traits, but in warming and drying climates, root traits may be critical, and seedlings may be the vulnerable stage. Relationships of seedling and root traits to more commonly measured traits and ecological outcomes are poorly known. In an annual grassland where winter drought-induced seedling mortality is driving a long-term decline in native diversity, using a field experiment during the exceptionally dry winter of 2017-2018, we found that seedling mortality was higher and growth of seedlings and adults were lower in unwatered than watered sites. Mortality of unwatered seedlings was higher in species with shorter seedling roots, and also in species with the correlated traits of small seeds, high seedling specific leaf area (SLA), and tall seedlings. Adult traits varied along an axis from short-stature, high SLA and foliar N, and early flowering to the opposite values, and were only weakly correlated with seedling traits and seedling mortality. No evidence was found for adaptive plasticity, such as longer roots or lower SLA in unwatered plants. Among these species, constitutive variation in seedling root length explained most of the variation in survival of a highly vulnerable life stage under winter drought. Selective loss of species with high adult SLA, observed in this community and others under drought stress, may be the byproduct of other correlated traits.
基于特征的方法越来越多地被用于预测气候变化对生态的影响，但植物特征与观察到的气候驱动群落变化之间很少建立起坚实的联系。大多数分析都集中在地上成年植物特征上，但在气候变暖干燥的情况下，根特征可能是至关重要的，而幼苗可能是脆弱的阶段。幼苗和根特征与更常见的测量特征和生态结果之间的关系知之甚少。在一个一年生草原中，冬季干旱导致幼苗死亡，正在推动本地多样性的长期下降，在 2017-2018 年异常干燥的冬季期间进行的一项野外实验中，我们发现，未浇水的地方比浇水的地方幼苗死亡率更高，幼苗和成年植物的生长速度更慢。未浇水幼苗的死亡率在幼苗根系较短的物种中更高，在具有相关特征的物种中也是如此，这些特征包括小种子、高幼苗比叶面积（SLA）和高大的幼苗。成年植物特征沿短株高、高 SLA 和叶片氮、早开花的轴变化，与幼苗特征和幼苗死亡率的相关性较弱。在未浇水的植物中没有发现适应性可塑性的证据，例如根更长或 SLA 更低。在这些物种中，幼苗根长的组成性变异解释了冬季干旱下高度脆弱生命阶段的生存变化的大部分。在这种社区和其他干旱胁迫下观察到的具有高成年 SLA 的物种的选择性丧失，可能是其他相关特征的副产品。
