Plants make leaf-level trade-offs between photosynthetic carbon assimilation and water loss, and the optimal balance between the two is dependent, in part, on water availability. “Conservative” water-use strategies, in which minimizing water loss is prioritized over assimilating carbon, tend to be favored in arid environments, while “aggressive” water-use strategies, in which carbon assimilation is prioritized over water conservation, are often favored in mesic environments. When derived from foliar carbon isotope ratios, intrinsic water-use efficiency (iWUE) serves as a seasonally integrated indicator of the balance of carbon assimilation to water loss at the leaf level. Here, we used a multi-decadal record of annual iWUE, growth, and flowering from a single population of Encelia farinosa in the Mojave Desert to evaluate the effect of iWUE on plant performance across interannual fluctuations in water availability. We identified substantial variability in iWUE among individuals and found that iWUE interacted with water availability to significantly influence growth and flowering. However, the relationships between iWUE, water availability, and plant performance did not universally suggest that “conservative” water-use strategies were advantageous in dry years or that “aggressive” strategies were advantageous in wet years. iWUE was positively related to the odds of growth regardless of water availability and to the odds of flowering in dry years, but negatively related to growth rates in dry years. In addition, we found that leaf nitrogen content affected interannual plant performance and that an individual’s iWUE plasticity in response to fluctuations in aridity was negatively related to early life drought survival and growth.

植物在光合碳同化和水分流失之间进行叶级权衡，两者之间的最佳平衡部分取决于水的可用性。“保守”用水策略，在干旱环境中，尽量减少水分流失优先于吸收碳，而“积极”用水策略，其中碳同化优先于节约用水，通常在干旱环境中受到青睐。中等环境。当从叶面碳同位素比率得出时，内在水分利用效率 (iWUE) 可作为季节性综合指标，用于衡量叶片水平上碳同化与水分流失之间的平衡。在这里，我们使用了一个单一的Encelia farinosa种群的年度 iWUE、生长和开花的多年记录在莫哈韦沙漠中，以评估 iWUE 对可用水年际波动的植物性能的影响。我们确定了个体之间 iWUE 的显着差异，并发现 iWUE 与可用水量相互作用以显着影响生长和开花。然而，iWUE、可用水量和植物性能之间的关系并不普遍表明“保守”用水策略在干旱年份有利或“积极”策略在丰水年份有利。iWUE 与不考虑可用水量的生长几率和干旱年份开花几率呈正相关，但与干旱年份的增长率呈负相关。此外，