LAUSR

Sand rice (Agriophyllum squarrosum) is broadly distributed on sand dunes in Arid Asia Interior. Large intraspecific trait variation makes it as an optimal model to investigate the ecological process underlying the adaptation to desert environment. In this study, seed size variation across 68 natural populations was used to determine the geographic pattern and to quantify the effects of climate, soil, and collection-year weather variables. Seed major axis and thousands of seed weight (TSW) both showed significant longitudinal patterns. Long-term climate variables accounted for most of the explained variances of major axis (57.20%) and TSW (91.54%). Specifically, annual precipitation and PPTmin had the most significantly positive and negative effects, indicating that longitudinal clines are driven by a precipitation gradient across its distribution range. Substantial unique effect of soil variables (27.27%) was found for major axis variation, but only was 3.64% of TSW variation explained by soil variables. Two extreme groups were selected to evaluate the genetic and plastic effects on seed size in a common garden. Large-seeded individuals were more competitive in semi-arid regions, and had stronger adaptive plasticity, as well as better performance in early seedling establishment. Therefore, the large-seeded genotypes merit the following sand rice domestication and breeding.