Context Disturbances may affect the spatial patterns of plant genetic diversity, but these effects are not yet well understood for lack of direct experimental evidence. Grazing is one of such environmental disturbance factors which may lead to small-scale spatial heterogeneity in natural grasslands. Objectives Our main goal was to determine whether a grazing disturbance alters population genetic diversity and genetic structure of the dominant species in the Inner Mongolia Steppe. Methods We performed inter-simple sequence repeat (ISSR) molecular marker analysis on populations of Stipa grandis and S. krylovii which were exposed to five consecutive years of varying degrees of grazing disturbance. Results The amplification results showed that the genetic diversity of both S. grandis and S. krylovii populations varied under different grazing intensities; the highest diversity (Nei's index and Shannon's index) were under moderate disturbance, whereas the lowest under the heavy grazing. The coefficient of gene differentiation (G ST ) of S. grandis and S. krylovii populations were 16.82 and 21.00°%, respectively. These results suggest that the genetic diversity of these two dominant populations was altered by the smallscale grazing disturbance, which provides new evidence supporting the theories of landscape genetics. Conclusions The enhancement of moderate grazing on genetic diversity implies the necessity to involve animal grazing in the design of management regimes for biodiversity conservation of the Inner Mongolia steppes.
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