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Background and Aims

In water limited landscapes, some plants build structures that enable them to survive with minimal water (drought resistance). Instead of making structures that allow for survival through times of water limitation, annual plants may invoke a drought escape strategy where they complete growth and reproduction when water is available. Drought escape and resistance each require a unique combination of traits and, therefore, plants are likely to have a suite of trait values that are consistent with a single drought response strategy. In environments where conditions are variable, plants may additionally evolve phenotypically plastic trait responses to water availability. Invasive annual species commonly occur in arid and semi-arid environments and many will be subject to reduced water availability associated with climate change. Assessing intraspecific trait variation across environmental gradients is a valuable tool for understanding how invasive plants establish and persist in arid environments. Methods

In this study, we used a common garden experiment with two levels of water availability to determine how traits related to carbon assimilation, water use, biomass allocation, and flowering phenology vary in California wild radish populations across an aridity gradient. Key Results

We found that populations from arid environments have rapid flowering and increased allocation to root biomass; traits associated with both drought escape and tolerance. Early flowering was associated with higher leaf nitrogen concentration and lower leaf mass per area; traits associated with high resource acquisition. While trait values varied across low- and high-water treatments, these shifts were consistent across populations indicating no differential plasticity across the aridity gradient. Conclusions

While previous studies have suggested that drought escape and drought resistance are mutually exclusive drought response strategies, our findings suggest that invasive annuals may employ both strategies to succeed in novel semi-arid environments. As many regions are expected to become more arid in the future, investigations of intraspecific trait variation within low water environments help to inform our understanding of potential evolutionary responses to increased aridity in invasive species.


This is a pre-copy-editing, author-produced PDF of an article accepted for publication in Annals of Botany following peer review. The definitive publisher-authenticated version is available online at


Oxford University Press

Available for download on Sunday, September 19, 2021