Local habitat condition rather than geographic distance determines the genetic structure of Tamarix chinensis populations in Yellow River Delta, China

Understanding the extent of genetic diversity in natural populations and the correlations between population structure and environmental heterogeneity is of great importance to estimation of the potential for species to undergo rapid adaptive changes in response to environmental variation. In this study, we systematically sampled 800 individuals from 26 Tamarix chinensis populations distributed throughout the Yellow River Delta (YRD) region in China, where a mosaic of habitat patches varying in soil salinity was detected. By exploring the micro-geographic genetic structure using the co-dominant microsatellite (SSR) markers, we aimed to answer questions as to what extent the populations diverged and how habitat heterogeneity affected the local population structure and dynamics of T. chinensis in YRD. The results demonstrated a moderate high level of genetic diversity and a low level of genetic differentiation in T. chinensis populations. The genetic variation was mainly maintained within populations, with a weak but significant genetic differentiation being detected among populations (Fst = 0.053, P < 0.001). While the overall genetic diversity within populations decreased progressively along with the increasing soil salinity, the locus T1D12 exhibited an elevated variation among populations, with the allele 558 (T1D12) showing a significantly higher frequency in highly saline habitats than in other sites, suggesting that the ecological differences among patchy habitats led to weak but significant adaptive divergence among populations. Local habitat conditions rather than geographic distances determine the genetic structure of T. chinensis populations in YRD.