Natural grasslands are an important renewable resource for livestock production. Grazing in these areas alters the plant community composition, litter quality, and soil microbial structure and activity. Three cool-season species were studied in a semiarid rangeland area of Argentina: Poa ligularis and Nassella tenuis (desirable/preferred for livestock) and Amelichloa ambigua (undesirable/non preferred). The objective was to analyze the effect of moderate defoliation and plant species on the structure and activity of soil microbial communities associated with their roots. In winter 2012, soil samples (0–10 cm) were taken underneath marked plant canopies of the three species (n = 8). Immediately thereafter, half of the plants (n = 4) were defoliated (5 cm stubble height) and the other half remained undefoliated (controls). The defoliation treatment was conducted again in the spring. Soil samples were taken 30 days after each defoliation event. The study was repeated in 2013, using a different plant set. Bacterial community structure and soil microbial activity were analyzed using PCR-DGGE analysis and basal soil respiration, respectively. Moderate and early defoliations allowed compensatory growth in the defoliated plants. Variations in the soil genetic profiles of A. ambigua suggest a higher dependence on its rhizospheric bacterial communities. Defoliation treatments did not substantially affect basal soil respiration but showed strong links between desirable species and soil microbial activity. Sustainable management practices that promote the persistence of these species are important for the development of microbial communities that respond quickly to stress conditions, favoring decomposition processes that maintain soil fertility in semiarid grasslands.

天然草原是畜牧生产的重要可再生资源。在这些地区放牧会改变植物群落组成、凋落物质量以及土壤微生物结构和活动。在阿根廷的一个半干旱牧场地区研究了三种凉爽季节的物种：Poa ligularis和Nassella tenuis（适合/喜欢饲养牲畜）和Amelichloa ambigua（不受欢迎/不受欢迎）。目的是分析适度落叶和植物种类对与其根相关的土壤微生物群落结构和活性的影响。2012 年冬季，在三个物种（n = 8）的标记植物冠层下方采集了土壤样本（0-10 厘米）。紧接着，一半的植物（n = 4）脱叶（5 厘米留茬高度），另一半保持未脱叶（对照）。春季再次进行落叶处理。在每次落叶事件后 30 天采集土壤样品。该研究于 2013 年使用不同的植物组重复进行。分别使用PCR-DGGE分析和基础土壤呼吸分析了细菌群落结构和土壤微生物活性。中度和早期落叶允许落叶植物的补偿性生长。土壤遗传谱的变化A. ambigua表明对其根际细菌群落的依赖性更高。落叶处理并未显着影响基础土壤呼吸，但显示出所需物种与土壤微生物活动之间的密切联系。促进这些物种持久性的可持续管理实践对于快速响应压力条件的微生物群落的发展很重要，有利于保持半干旱草原土壤肥力的分解过程。