Current distribution of C and C grasses is often explained by contrasting environmental conditions. Regions where C and C grasses coexist, as the Southeastern South America grasslands (SESA grasslands), provides an excellent opportunity to investigate the evolutionary imprints of grasses through clade distribution patterns. Here, we aimed to understand how ecological and evolutionary processes affect the phylogenetic diversity of grass communities along 666 sites located in a latitudinal gradient ranging from 26°S to 38°S in SESA grasslands (Argentina, Brazil, and Uruguay). We applied generalized linear models (GLM) to understand the role of the different environmental and historical drivers that shape the proportion of C grasses distribution in SESA grasslands. The effect of latitude on phylogenetic beta-diversity patterns among the vegetation surveys was evaluated through principal coordinates of phylogenetic structure. Contribution of C species increased southwards (R² = 0.40, P<0.001). C species are more likely to occur in colder areas with higher historical temperature stability, reflecting lineages that have specialized and radiated in cold environments (GLM results: R² = 0.37, P<0.01). Climatically stable areas are the coldest, while unstable areas include warmer habitats, which enabled colonization by C species. Regarding soil conditions, C grasses are more likely to occur in more fertile soils and with low capacity to retain water (GLM results: pseudo-R² = 0.37, P<0.01). We found that phylogeny has an important role as a structuring agent of grass communities across our study region, indicating turnover of grass lineages along the latitudinal gradient. Grass species found at the northern portion of the gradient belong mostly to the clade which contain both C and C species. At the southern part of the gradient, communities are dominated by grasses belonging to a C-exclusive clade. The distribution of grass clades across the SESA grasslands is indicative of the environmental gradients found in this region between temperate and tropical zones, describing a climate space where disturbance driven feedbacks play a major role in maintaining open vegetation. Our results contribute to the understanding of ecological and evolutionary drivers of grass distribution in the region that up to now has been poorly described.

中文翻译：

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南美洲草原草生物地理分布的决定因素

C 和 C 草的当前分布通常是通过对比环境条件来解释的。 C 和 C 草共存的地区，如南美洲东南部草原（SESA 草原），为通过分支分布模式研究草的进化印记提供了绝佳的机会。在这里，我们旨在了解生态和进化过程如何影响 SESA 草原（阿根廷、巴西和乌拉圭）南纬 26° 至 38° 纬度梯度范围内 666 个地点草群落的系统发育多样性。我们应用广义线性模型 (GLM) 来了解影响 SESA 草原中 C 草分布比例的不同环境和历史驱动因素的作用。通过系统发育结构主坐标评估纬度对植被调查中系统发育β多样性模式的影响。 C物种的贡献向南增加(R² = 0.40, P<0.001)。 C物种更有可能出现在历史温度稳定性较高的寒冷地区，反映了在寒冷环境中特化和辐射的谱系（GLM结果：R² = 0.37，P<0.01）。气候稳定的地区是最冷的，而不稳定的地区包括较温暖的栖息地，这使得 C 物种能够定居。关于土壤条件，C 草更有可能出现在较肥沃且保水能力较低的土壤中（GLM 结果：pseudo-R² = 0.37，P<0.01）。我们发现，系统发育作为我们研究区域草类群落的结构因素发挥着重要作用，表明草类谱系沿纬度梯度的更替。在梯度北部发现的草种大多属于同时含有 C 和 C 种的分支。在梯度的南部，群落以属于 C 专属分支的草类为主。 SESA 草原上草支的分布表明了该地区温带和热带之间的环境梯度，描述了干扰驱动的反馈在维持开放植被方面发挥主要作用的气候空间。我们的研究结果有助于了解该地区草分布的生态和进化驱动因素，而迄今为止对此的描述还很少。