Interactions among intrinsic water-use efficiency and climate influence growth and flowering in a common desert shrub

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.

Automated summary

Plants make trade-offs between photosynthesis and water loss, favoring conservative water-use strategies in arid environments and aggressive strategies in mesic environments. Intrinsic water-use efficiency (iWUE) serves as an indicator of the balance between carbon assimilation and water loss, influencing plant performance across interannual fluctuations. Relationships between iWUE, water availability, and plant performance are complex and vary depending on factors such as leaf nitrogen content and individual plasticity in response to aridity fluctuations.