Grazing intensity significantly affects belowground carbon and nitrogen cycling in grassland ecosystems: a meta‐analysis

Abstract

Livestock grazing activities potentially alter ecosystem carbon (C) and nitrogen (N) cycles in grassland ecosystems. Despite the fact that numerous individual studies and a few meta-analyses had been conducted, how grazing, especially its intensity, affects belowground C and N cycling in grasslands remains unclear. In this study, we performed a comprehensive meta-analysis of 115 published studies to examine the responses of 19 variables associated with belowground C and N cycling to livestock grazing in global grasslands. Our results showed that, on average, grazing significantly decreased belowground C and N pools in grassland ecosystems, with the largest decreases in microbial biomass C and N (21.62% and 24.40%, respectively). In contrast, belowground fluxes, including soil respiration, soil net N mineralization and soil N nitrification increased by 4.25%, 34.67% and 25.87%, respectively, in grazed grasslands compared to ungrazed ones. More importantly, grazing intensity significantly affected the magnitude (even direction) of changes in the majority of the assessed belowground C and N pools and fluxes, and C : N ratio as well as soil moisture. Specifically,light grazing contributed to soil C and N sequestration whereas moderate and heavy grazing significantly increased C and N losses. In addition, soil depth, livestock type and climatic conditions influenced the responses of selected variables to livestock grazing to some degree. Our findings highlight the importance of the effects of grazing intensity on belowground C and N cycling, which may need to be incorporated into regional and global models for predicting effects of human disturbance on global grasslands and assessing the climate-biosphere feedbacks.

Drought‐induced changes in root biomass largely result from altered root morphological traits: Evidence from a synthesis of global field trials

“…Our meta‐analysis also found that drought significantly increased R/S (Figure c; Table S1), which was consistent with the results from Pallardy and Rhoads () and Aspelmeier and Leuschner (). Increased R/S is a plant avoidance mechanism in response to drought when drought increases the proportion of RB relative to aboveground biomass (Hermans, Hammond, White, & Verbruggen, ; Hodge, ; Zhou et al, ). Meanwhile, the response of R/S to drought varied among plant functional types (Figure ), which might be attributed to the different strategies of plant functional types to obtain water and nutrients and distribution of RB at different soil profile (Daryanto et al, ).…”

“…Well‐designed experiments are thus necessary to comprehensively examine the response of diverse root traits and other ecosystem processes to drought (Fotelli et al, ). Third, global climate change often incorporates simultaneous changes in multiple environmental factors (e.g., rising temperature, precipitation, nitrogen addition, and elevated CO 2 ), which may interactively influence root traits (Zhou et al, ). However, despite the fact that our current study indicated the importance of drought on root traits, the interactions between drought and multiple climate factors on root traits in terrestrial ecosystems still remained uncertain.…”

Grassland Management Affects Delivery of Regulating and Supporting Ecosystem Services

“…A meta-analysis of 115 published studies found that grazing intensity affected the magnitude and direction of most belowground C and N pools and fluxes, with light grazing contributing to soil C and N sequestration, whereas moderate and heavy grazing significantly increasing C and N losses (Zhou et al, 2017). A global review and meta-analysis of 83 studies of extensively managed grasslands found an interaction of grazing intensity and regional climate for soil C accumulation (Abdalla et al, 2018).…”

Responses of growing‐season soil respiration to water and nitrogen addition as affected by grazing intensity

“…Livestock grazing is a global land‐use activity with a wide‐range of effects on key biotic and abiotic variables and hence on terrestrial carbon cycling (Selsted et al., ; Zhou et al., ). Because most previous grazing experiments have lasted <10 years (Zhao et al., ; Zhou et al., ), they were unable to detect the underlying mechanisms of how long‐term grazing affects soil carbon processes by changing biotic and abiotic parameters. Although the individual effects of nitrogen deposition and precipitation change on soil respiration are relatively well understood, how their effects on soil respiration are altered by long‐term grazing have rarely been assessed, especially under different grazing intensities.…”