The Tanggula Mountains enhance population divergence in Carex moorcroftii: a dominant sedge on the Qinghai-Tibetan Plateau.

High-altitude mountains are often geographic barriers to gene flow and play important roles in shaping population divergence. The central Qinghai-Tibetan Plateau (QTP) stands the location of the Tanggula Mountains (TM). We use the TM as a case, using Carex moorcroftii, a dominant species on the QTP to test the effects of geographic barriers on plant population divergence. We sampled 18 C. moorcroftii populations along a north-south transect crossing the TM to investigate the correlations of genetic variation and morphological traits with climate variables. The results showed this species holds high genetic diversity (H = 0.58) and the surveyed populations can be genetically clustered into two groups: populations from the north face of TM, and the other from the south. Gene flow between populations within groups is higher than those between groups. The traits, number and mass of seeds, mass of root and infructescence significantly varied among populations. Mantel-tests detected a weak but significantly positive correlation between genetic and geographic (R = 0.107, p = 0.032) and climatic distance (R = 0.162, p = 0.005), indicating both isolation by distance and isolation by environment. These findings together suggest high-altitude mountains of TM interrupt habitat continuity, result in distinct climatic conditions on both sides, increasing population divergence of plant species.