While tree rings have enabled interannual examination of the influence of climate on trees, this is not possible for most shrubs. Here, we leverage a multidecadal record of annual foliar carbon isotope ratio collections coupled with 39 y of survey data from two populations of the drought-deciduous desert shrub Encelia farinosa to provide insight into water-use dynamics and climate. This carbon isotope record provides a unique opportunity to examine the response of desert shrubs to increasing temperature and water stress in a region where climate is changing rapidly. Population mean carbon isotope ratios fluctuated predictably in response to interannual variations in temperature, vapor pressure deficit, and precipitation, and responses were similar among individuals. We leveraged the well-established relationships between leaf carbon isotope ratios and the ratio of intracellular to ambient CO₂ concentrations to calculate intrinsic water-use efficiency (iWUE) of the plants and to quantify plant responses to long-term environmental change. The population mean iWUE value increased by 53 to 58% over the study period, much more than the 20 to 30% increase that has been measured in forests [J. Peñuelas, J. G. Canadell, R. Ogaya, Glob. Ecol. Biogeogr. 20, 597–608 (2011)]. Changes were associated with both increased CO₂ concentration and increased water stress. Individuals whose lifetimes spanned the entire study period exhibited increases in iWUE that were very similar to the population mean, suggesting that there was significant plasticity within individuals rather than selection at the population scale.

虽然树木年轮可以对气候对树木的影响进行年际检查，但这对于大多数灌木来说是不可能的。在这里，我们利用多年叶面碳同位素比收集记录以及来自干旱落叶沙漠灌木Encelia farinosa两个种群的 39 年调查数据，来深入了解用水动态和气候。该碳同位素记录提供了一个独特的机会来研究气候快速变化地区沙漠灌木对温度升高和水分胁迫的反应。人口平均碳同位素比率可预测地波动，以响应温度、蒸气压不足和降水的年际变化，并且个体之间的反应相似。_{我们利用叶片碳同位素比率与细胞内与环境CO 2}浓度比率之间的既定关系来计算植物的内在水分利用效率（iWUE）并量化植物对长期环境变化的响应。研究期间，人口平均 iWUE 值增加了 53% 至 58%，远高于在森林中测得的 20% 至 30% 的增幅 [J. Peñuelas、JG Canadell、R. Ogaya、Glob。生态。生物地质学。20, 597–608 (2011)]。_{变化与CO 2}浓度增加和水分胁迫增加相关。一生跨越整个研究期间的个体表现出 iWUE 的增加，与群体平均值非常相似，这表明个体内部存在显着的可塑性，而不是群体规模的选择。