Abstract In dry steppes, strong climatic constraints, especially highly variable precipitation, and grazing are the most important factors controlling plant life. Growth is strongly limited by water availability, while grazing may affect species presence and performance. However, there is a lack of studies on population genetics of dryland plants in general, and of those addressing grazing effects in particular. To determine the landscape-scale genetic structure of dryland species, and if grazing has an impact on that, we chose the Eurasian steppe grass Stipa glareosa for a population genetic study employing nine polymorphic Simple Sequence Repeat (SSR) markers. We assessed genetic fingerprints of 200 individuals from six populations in Mongolia, which were sampled along a large-scale precipitation and altitudinal gradient. Nested within this gradient, sub-populations were sampled along short local transects representing different grazing intensities. Overall, S. glareosa populations showed rather low levels of genetic diversity at a mean Bruvo distance among individuals within a given population of 0.494 (mean expected heterozygosity He = 0.053). Linear mixed model analysis implied that genetic diversity was affected by both climatic constraints and local grazing conditions. We found a moderate isolation-by-distance pattern across all populations; grazing additionally influenced the genetic structure at local scale. Analysis of Molecular Variance revealed a modest genetic differentiation between populations (9 % of variation) and among sub-populations representing different grazing levels (11 %). Moreover, we detected indicator alleles that were exclusive for populations along the precipitation gradient; other alleles were associated with certain grazing levels across all populations. Thus, our data suggest that climatic constraints affect the genetic structure of S. glareosa populations, while at local scales differences in grazing disturbance may also matter.

中文翻译：

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气候和土地利用影响针茅 PA Smirn 的遗传结构。在蒙古

摘要 在干旱草原，强烈的气候约束，特别是降水变化很大，放牧是控制植物生命的最重要因素。生长受到可用水量的严重限制，而放牧可能会影响物种的存在和表现。然而，缺乏对一般旱地植物群体遗传学的研究，特别是针对放牧影响的研究。为了确定旱地物种的景观尺度遗传结构，如果放牧对此有影响，我们选择欧亚草原草 Stipa glareosa 进行种群遗传研究，使用九个多态性简单序列重复 (SSR) 标记。我们评估了来自蒙古六个种群的 200 个个体的遗传指纹，这些个体是沿着大规模降水和海拔梯度采样的。嵌套在此梯度内，沿代表不同放牧强度的短局部横断面对亚群进行采样。总体而言，S. glareosa 种群在给定种群内个体之间的平均 Bruvo 距离为 0.494（平均预期杂合性 He = 0.053）时显示出相当低的遗传多样性水平。线性混合模型分析表明遗传多样性受气候限制和当地放牧条件的影响。我们在所有人群中发现了中等的距离隔离模式；放牧还影响了当地规模的遗传结构。分子变异分析揭示了种群之间（变异的 9%）和代表不同放牧水平的亚种群之间（11%）的适度遗传差异。而且，我们检测到沿降水梯度种群独有的指示等位基因；其他等位基因与所有种群的某些放牧水平相关。因此，我们的数据表明气候限制会影响 S. glareosa 种群的遗传结构，而在局部尺度上，放牧干扰的差异也可能很重要。