Adjustments in physiological and morphological traits suggest drought-induced competitive release of some California plants.

Drought and competition affect how morphological and physiological traits are expressed in plants. California plants were previously found to respond less negatively to resource limitation compared to invasive counterparts. In a glasshouse in Santa Cruz, CA, USA, we exposed five native California C grassland species to episodic drought and competition (via five locally invasive species). We hypothesized that leaf morphology would be more affected by competition, and leaf photosynthetic gas exchange more so by drought, consistent with optimal partitioning and environmental filter theories. We expected that traits would exhibit trade-offs along a spectrum for resource conservatism acquisition. had greater photosynthetic recovery, while had lower percent loss of net assimilation (PLA) and intrinsic water-use efficiency (WUE) during drought and competition simultaneously compared to just drought. and gas exchange was unaffected by drought, and leaf morphology exhibited drought-related adjustments. exhibited trait adjustments for competition but not drought. Functional traits sorted onto two principal components related to trade-offs for resource conservatism acquisition, and for above- belowground allocation. In summary, morphological traits were affected by competition and drought, whereas physiological traits, like leaf gas exchange, were primarily affected by drought. The grassland plants we studied showed diverse responses to drought and competition with trait trade-offs related to resource conservatism acquisition, and for above- belowground allocation consistent with optimal partitioning and environmental filter theories. experienced competitive release based on greater WUE and lower PLA when facing drought and competition.