Diversity in non-linear responses to soil moisture shapes evolutionary constraints in Brachypodium.

Abstract

Water availability is perhaps the greatest environmental determinant of plant yield and fitness. However, our understanding of plant-water relations is limited because-like many studies of organism-environment interaction-it is primarily informed by experiments considering performance at two discrete levels-wet and dry-rather than as a continuously varying environmental gradient. Here we used experimental and statistical methods based on function-valued traits to explore genetic variation in responses to a continuous soil moisture gradient in physiological and morphological traits among ten genotypes across two species of the model grass genus Brachypodium. We find that most traits exhibit significant genetic variation and non-linear responses to soil moisture variability. We also observe differences in the shape of these non-linear responses between traits and genotypes. Emergent phenomena arise from this variation including changes in trait correlations and evolutionary constraints as a function of soil moisture. Our results point to the importance of considering diversity in non-linear organism-environment relationships to understand plastic and evolutionary responses to changing climates.