Cool-season perennial grasslands are commonly used for livestock pasture. However, understanding of the belowground effects of forage defoliation (selective pressure applied by grazing) management is nascent. We investigated how defoliation management affects aboveground (forage productivity) and belowground processes (soil C/N), microbial nutrient cycling, and potential nitrous oxide [N₂O] emissions). We hypothesized that rotational (moderate frequency) defoliation at low severity will increase soil organic matter (SOM) storage and microbial capacity to cycle C, N, and P, but that these changes would also lead to greater soil N₂O emission potential. Data were collected from organically (OF) and conventionally managed (CF) farms with differing botanical composition in West Virginia, where three frequencies and two severities of forage defoliation were imposed. At OF, more severe defoliation decreased labile soil C content (–26%), while moderate defoliation resulted in a 39% reduction in microbial enzymatic capacity to cycle C, but not at CF. The N₂O emission potential (ratio of nirK/nosZ functional gene abundance), was differentially affected by defoliation treatments at both sites. At OF, defoliation severity altered N₂O emission potential, whereby low severity resulted in an 82% decrease in potential N₂O emissions compared with high severity treatments. At CF, continuously defoliated plots exhibited a 71% lower N₂O emission potential relative to less frequent defoliation. Belowground microbial parameters were more responsive to defoliation at OF, suggesting past management may influence how grazing management asserts belowground changes. Results suggest that defoliation management could enhance soil C storage, but potentially at the risk of increased N₂O emissions.

中文翻译：

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规定的落叶策略影响牧场的土壤碳和一氧化二氮潜力

凉季多年生草原常用于牲畜牧场。然而，对牧草落叶（放牧施加的选择性压力）管理的地下影响的理解是新生的。我们调查了落叶管理如何影响地上（草料生产力）和地下过程（土壤 C/N）、微生物养分循环和潜在的一氧化二氮 [N ₂ O] 排放）。我们假设低强度的轮换（中等频率）落叶会增加土壤有机质 (SOM) 的储存和微生物循环 C、N 和 P 的能力，但这些变化也会导致土壤 N _2增加O 排放潜力。数据是从西弗吉尼亚州植物成分不同的有机 (OF) 和常规管理 (CF) 农场收集的，其中实施了三种频率和两种严重程度的牧草落叶。在 OF，更严重的落叶降低了不稳定土壤 C 含量 (–26%)，而适度的落叶导致微生物酶循环 C 的能力降低了 39%，但在 CF 没有。N ₂ O 排放潜力（nirK/nosZ功能基因丰度的比率）受到两个地点的落叶处理的不同影响。在 OF，落叶严重程度改变了 N ₂ O 排放潜力，因此低严重程度导致潜在 N _{2减少 82%}与高强度处理相比的 O 排放。在 CF 处，连续落叶地块的 N ₂ O 排放潜力比不那么频繁落叶低 71%。地下微生物参数对 OF 的落叶反应更敏感，这表明过去的管理可能会影响放牧管理如何断言地下变化。结果表明，落叶管理可以提高土壤碳储存量，但可能存在增加 N ₂ O 排放的风险。