Table_2_Functional Traits Explain Variation in Chaparral Shrub Sensitivity to Altered Water and Nutrient Availability.DOCX

Worldwide drylands are threatened by changes in resource availability associated with global environmental change. Functional traits may help predict which species will be most responsive to these alterations in nutrient and water availability. Current functional trait work focuses on tissue construction and nutrient concentrations, but plant performance in low resource environments also may be strongly influenced by traits related to nutrient budgets and allocation. Our overall objective was to compare trait responses in a suite of serpentine and nonserpentine congener pairs from the California chaparral, a biodiverse region facing nutrient deposition and future changes in precipitation. In a common garden greenhouse environment, we grew small plants of Arctostaphylos manzanita, A. viscida, Ceanothus cuneatus, C. jepsonii, Quercus berberidifolia, and Q. durata in contrasting soil nutrient and moisture treatments. We measured a suite of traits representing physiological, growth, and mineral nutrient responses to these treatments. Overall, plant growth rate and leaf-level phosphorus use efficiency were greatest in the low water, high nutrient treatment, and lowest in the high water, low nutrient treatment. Variation in growth rate and plasticity among species and treatments was primarily associated with differences in mineral nutrition-based traits as opposed to differences in biomass allocation or specific leaf area. Namely, faster growing species and species with greater plasticity allocated more nitrogen and phosphorous to leaves and demonstrated greater photosynthetic phosphorus use efficiency. Overall, nonserpentine species had greater plasticity and biomass response to resource addition than serpentine species, and congener pairs responded to these resource additions more similarly to each other than species across congener pairs. This study extends our general understanding of how functional traits may influence species responses to environmental change and highlights the need to integrate mineral nutrition-based traits, including allocation of nutrient pools and nutrient use efficiency into this larger trait framework. Ultimately, this insight can help identify, in part, why coexisting species may vary in sensitivity to anthropogenic driven changes in soil resource availability.

全球干旱地区正面临着与全球环境变化相关的资源可利用性改变带来的威胁。功能性状（functional traits）或可预测哪些物种对养分与水分可利用性的改变响应最为强烈。当前的功能性状研究多聚焦于组织构建与养分浓度，但低资源环境下的植物表现，也可能受到养分收支与分配相关性状的显著影响。本研究的总体目标是，针对面临养分沉降与未来降水变化的生物多样性热点区域——加州沙巴拉灌丛带，选取一组蛇纹岩土与非蛇纹岩土的同属物种对，比较其性状响应差异。在温室同质园环境中，我们栽培了6个物种的幼苗：熊果属（Arctostaphylos）的A. manzanita、A. viscida，美洲茶属（Ceanothus）的C. cuneatus、C. jepsonii，以及栎属（Quercus）的Q. berberidifolia、Q. durata，并设置了不同的土壤养分与水分处理梯度。我们测定了一系列表征植株对上述处理的生理、生长及矿质养分响应的性状指标。总体而言，植株的生长速率与叶片磷利用效率（phosphorus use efficiency）在低水分、高养分处理组中最高，而在高水分、低养分处理组中最低。不同物种与处理间的生长速率及可塑性变异，主要与基于矿质养分的性状差异相关，而非生物量分配或比叶面积（specific leaf area）的差异。具体而言，生长速率更快、可塑性更强的物种，会将更多的氮与磷分配至叶片，并表现出更高的光合磷利用效率。总体而言，非蛇纹岩土物种对资源添加的可塑性与生物量响应均强于蛇纹岩土物种；且同属物种对之间的资源添加响应，相较于跨属物种对更为相似。本研究深化了我们对功能性状如何影响物种对环境变化响应的一般性认知，并强调需将基于矿质养分的性状——包括养分库分配与养分利用效率——纳入更大尺度的性状研究框架中。最终，该研究结论可在一定程度上帮助解析共存物种对人为驱动的土壤资源可利用性变化的敏感性差异成因。