AIM: Livestock grazing can alter carbon (C), nitrogen (N) and phosphorus (P) cycles, thereby affecting the C : N : P stoichiometry in grasslands. In this study, we aimed to examine mechanisms underlying the impacts of grazing on grassland C : N : P stoichiometry, focusing on belowground processes and their linkages with aboveground vegetation properties. LOCATION: Global. TIME PERIOD: 1900–2018. MAJOR TAXA STUDIED: Grassland ecosystems. METHODS: We conducted a meta‐analysis based on 129 published studies to synthesize the effects of grazing on the C : N : P stoichiometry of leaves, stems, litter, roots, microbial biomass, and soil in grassland ecosystems. RESULTS: Grazing significantly affected the C, N and P pools, and then the C : N : P stoichiometry in grassland ecosystems. Grazing effects on C : N : P stoichiometry varied strongly with grazing intensity. Specifically, heavy grazing decreased all C : N : P stoichiometry except litter N : P and root C : N ratios, while light and moderate grazing caused less negative or positive effects. Grazing effects on litter C : N ratio were negatively correlated with grazing effects on soil C : N ratios under light and moderate grazing, but this relationship was positive under heavy grazing. In contrast, grazing effects on root C : P and soil C : P were positively correlated under light and moderate grazing but negatively correlated under heavy grazing. Importantly, grazing significantly decreased the soil N pool by 10.0% but increased the soil P pool by 3.6%, indicating differential mechanisms for grazing impact on N and P cycles in grasslands. MAIN CONCLUSIONS: Our results strongly suggest that grazing intensity regulates the biogeochemical cycles of C, N and P in grassland ecosystems by affecting plant nutrient use efficiency and soil physicochemical processes. Therefore, incorporating grazing intensity into Earth system models may improve predictions of climate–grassland feedbacks in the Anthropocene.

中文翻译：

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放牧强度显着改变草地生态系统中的 C : N : P 化学计量

目的：放牧可以改变碳 (C)、氮 (N) 和磷 (P) 循环，从而影响草原中的 C:N:P 化学计量。在这项研究中，我们旨在研究放牧对草地 C : N : P 化学计量学影响的潜在机制，重点关注地下过程及其与地上植被特性的联系。地点：全球。时间段：1900-2018。研究的主要类群：草原生态系统。方法：我们基于 129 项已发表的研究进行了荟萃分析，以综合放牧对草地生态系统中叶、茎、凋落物、根、微生物生物量和土壤的 C:N:P 化学计量的影响。结果：放牧显着影响了草地生态系统中的 C、N 和 P 库，然后是 C : N : P 化学计量。放牧对 C 的影响 : N : P 化学计量随放牧强度变化很大。具体而言，重度放牧降低了所有 C:N:P 化学计量比，除了凋落物 N:P 和根 C:N 比率，而轻度和中度放牧造成的负面或正面影响较小。在轻度和中度放牧下，放牧对凋落物C：N比的影响与放牧对土壤C：N比的影响呈负相关，但在重度放牧下这种关系呈正相关。相比之下，放牧对根C : P 和土壤C : P 的影响在轻度和中度放牧下呈正相关，而在重度放牧下呈负相关。重要的是，放牧显着降低了土壤 N 库 10.0%，但增加了 3.6% 土壤 P 库，表明放牧对草地 N 和 P 循环的影响不同。主要结论：我们的结果强烈表明，放牧强度通过影响植物养分利用效率和土壤物理化学过程来调节草地生态系统中 C、N 和 P 的生物地球化学循环。因此，将放牧强度纳入地球系统模型可能会改善对人类世气候-草地反馈的预测。