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Background and aims: The frequent occurrence of extreme rainfall events results in soils experiencing drying–rewetting (DRW) cycles. Such rewetting can lead to a surge in soil CO2 emissions; however, the main regulatory factors involved in this priming effect are unclear. Methods: In this study, we conducted a meta-analysis using data extracted from 43 published papers, to determine the direct regulatory factors involved in the priming effect of soil CO2. Results: The results indicated that the priming effect of rewetting on soil CO2 emissions was influenced by ecosystem type, soil properties, climatic factors, and the number of DRW cycles. The priming effect was the highest in cropland but the lowest in grassland when taking flux values observed before rewetting as the control group. It was also greater in acidic soils (pH < 6.5) and soils with a high clay fraction (clay ≥ 30%) than in other soils. The effect size (lnRR) of soil CO2 emissions was exponentially related to the mean annual precipitation (MAP), and decreased with increases in MAP. In DRW experiments, the priming effect of the first rewetting on soil CO2 emissions was the largest, an effect that gradually decreased with the number of DRW cycles, before disappearing completely. Most importantly, soil moisture influenced the peak time and the pulse time of the priming effect: the greater the change in soil moisture, the longer the peak time duration; the higher the maximum soil moisture content after rewetting, the longer the pulse time duration; and the lower the initial soil moisture content, the bigger the priming effect. Conclusion: Generally, physical mechanisms, especially soil moisture, directly regulate the CO2 priming effect during DRW cycles. Thus, this study provides a theoretical basis for assessing and predicting the impact of future precipitation changes on soil carbon cycling. Future studies should also carefully monitor any changes in soil microorganisms in response to changes in soil moisture during DRW cycles, because these appear to be significantly involved in CO2 release from soils. [ABSTRACT FROM AUTHOR]

Background and aims: Many meadows are experiencing severe degradation due to the effects of global climate change and other human-related activity, especially overgrazing. The impact of grazing may however vary in different sites, but the dynamics and mechanisms associated with grazing-related meadow degradation on soil microbial biomass structure and function in different locations are still unclear.To address this we examined three alpine meadows with different grazing sites in northwest China, which included grazing in winter and summer, in each of which there were four degradation gradients, varying from no degradation to severe degradation.At the Maqin site, grazing during the summer resulted in higher concentrations of microbial carbon (MBC), nitrogen (MBN), and phosphorus (MBP) compared to grazing during winter. Undegraded meadows (ND) also had higher MBC concentrations compared to low (LD), medium (MD), or severely degraded (SD) ones at the three sites. However, the homeostasis analysis revealed that the elemental stoichiometries were strictly controlled, despite significant degradation-related effects on the concentrations of MBC, MBN, and MBP, indicating relatively stable coupling relationships among C, N, and P.The random forest and partitioning variation analyses showed that edaphic factors play the more important roles in regulating microbial biomass and elemental composition in the different sites. Overall, these results suggest that the effects of degradation on soil microbial biomass concentrations and the stoichiometries are context dependent, particularly with regard to the impact of background soil properties, demonstrating that site conditions must be considered when predicting how grassland ecosystems will respond to grazing-related degradation.Methods: Many meadows are experiencing severe degradation due to the effects of global climate change and other human-related activity, especially overgrazing. The impact of grazing may however vary in different sites, but the dynamics and mechanisms associated with grazing-related meadow degradation on soil microbial biomass structure and function in different locations are still unclear.To address this we examined three alpine meadows with different grazing sites in northwest China, which included grazing in winter and summer, in each of which there were four degradation gradients, varying from no degradation to severe degradation.At the Maqin site, grazing during the summer resulted in higher concentrations of microbial carbon (MBC), nitrogen (MBN), and phosphorus (MBP) compared to grazing during winter. Undegraded meadows (ND) also had higher MBC concentrations compared to low (LD), medium (MD), or severely degraded (SD) ones at the three sites. However, the homeostasis analysis revealed that the elemental stoichiometries were strictly controlled, despite significant degradation-related effects on the concentrations of MBC, MBN, and MBP, indicating relatively stable coupling relationships among C, N, and P.The random forest and partitioning variation analyses showed that edaphic factors play the more important roles in regulating microbial biomass and elemental composition in the different sites. Overall, these results suggest that the effects of degradation on soil microbial biomass concentrations and the stoichiometries are context dependent, particularly with regard to the impact of background soil properties, demonstrating that site conditions must be considered when predicting how grassland ecosystems will respond to grazing-related degradation.Results: Many meadows are experiencing severe degradation due to the effects of global climate change and other human-related activity, especially overgrazing. The impact of grazing may however vary in different sites, but the dynamics and mechanisms associated with grazing-related meadow degradation on soil microbial biomass structure and function in different locations are still unclear.To address this we examined three alpine meadows with different grazing sites in northwest China, which included grazing in winter and summer, in each of which there were four degradation gradients, varying from no degradation to severe degradation.At the Maqin site, grazing during the summer resulted in higher concentrations of microbial carbon (MBC), nitrogen (MBN), and phosphorus (MBP) compared to grazing during winter. Undegraded meadows (ND) also had higher MBC concentrations compared to low (LD), medium (MD), or severely degraded (SD) ones at the three sites. However, the homeostasis analysis revealed that the elemental stoichiometries were strictly controlled, despite significant degradation-related effects on the concentrations of MBC, MBN, and MBP, indicating relatively stable coupling relationships among C, N, and P.The random forest and partitioning variation analyses showed that edaphic factors play the more important roles in regulating microbial biomass and elemental composition in the different sites. Overall, these results suggest that the effects of degradation on soil microbial biomass concentrations and the stoichiometries are context dependent, particularly with regard to the impact of background soil properties, demonstrating that site conditions must be considered when predicting how grassland ecosystems will respond to grazing-related degradation.Conclusion: Many meadows are experiencing severe degradation due to the effects of global climate change and other human-related activity, especially overgrazing. The impact of grazing may however vary in different sites, but the dynamics and mechanisms associated with grazing-related meadow degradation on soil microbial biomass structure and function in different locations are still unclear.To address this we examined three alpine meadows with different grazing sites in northwest China, which included grazing in winter and summer, in each of which there were four degradation gradients, varying from no degradation to severe degradation.At the Maqin site, grazing during the summer resulted in higher concentrations of microbial carbon (MBC), nitrogen (MBN), and phosphorus (MBP) compared to grazing during winter. Undegraded meadows (ND) also had higher MBC concentrations compared to low (LD), medium (MD), or severely degraded (SD) ones at the three sites. However, the homeostasis analysis revealed that the elemental stoichiometries were strictly controlled, despite significant degradation-related effects on the concentrations of MBC, MBN, and MBP, indicating relatively stable coupling relationships among C, N, and P.The random forest and partitioning variation analyses showed that edaphic factors play the more important roles in regulating microbial biomass and elemental composition in the different sites. Overall, these results suggest that the effects of degradation on soil microbial biomass concentrations and the stoichiometries are context dependent, particularly with regard to the impact of background soil properties, demonstrating that site conditions must be considered when predicting how grassland ecosystems will respond to grazing-related degradation. [ABSTRACT FROM AUTHOR]