Livestock excretion alleviates soil microbial carbon and phosphorus limitations relative to trampling and defoliation in an alpine meadow

Abstract

Livestock grazing significantly influence the carbon (C), nitrogen (N), and phosphorus (P) dynamics within grassland ecosystems. However, a limited understanding of the specific impacts of individual grazing behaviors—such as trampling, defoliation, and excretion—on the flexibility of C:N:P stoichiometry in soil systems still exists. To clarify this, we conducted field experiments to simulate various yak (Bos grunniens) grazing behaviors, including light and heavy trampling, light and heavy defoliation, and dung and urine deposition. These experiments aimed to assess their effects on the C:N:P stoichiometry of soil-microbe-enzyme in an alpine grassland. Our findings revealed that trampling significantly increased the microbial N:P and C:P ratios, compared to the control. Defoliation significantly raised microbial N:P and enzymatic C:P ratios, while excretion resulted in higher microbial C:N and enzymatic N:P ratios. Specifically, light defoliation led to significantly higher microbial C:N and C:P ratios than heavy defoliation. The imbalance in microbial C:N ratio intensified with greater defoliation intensity. Compared to trampling and defoliation, livestock excretion, especially dung deposition, potentially alleviated microbial C and P limitations by increasing the resource availability of soil microbial growth. Furthermore, microbial C:N:P stoichiometry responded more sensitively to grazing behaviors than soil C:N:P stoichiometry. Overall, our study distinguishes the independent effects of different yak grazing behaviors (trampling, defoliation, and excretion) on the C:N:P stoichiometry of soil-microbe-enzyme in an alpine grassland, and underscores the crucial role of soil microorganisms in moderating changes in C, N, and P cycling under livestock grazing.