A global meta-analysis on freeze-thaw effects on soil carbon and phosphorus cycling

Abstract Enhanced frequency and intensity of freeze-thaw cycle (FTC) owing to global climate change may influence soil carbon (C) and phosphorus (P) cycling in terrestrial ecosystems. However, a comprehensive understanding of soil C and P cycling in response to FTC is still lacking. Here, we compiled data of 2471 observations from 75 publications and conducted a meta-analysis on the responses of soil C and P cycling and the stoichiometry of C, N and P cycling to FTC. Results showed that experimental FTC significantly increased soil dissolved organic C (+38%), instant and cumulative CH4 (+41% and +59%, respectively), dissolved organic C leaching (+62%), total salt-extractable P (+27%), dissolved organic P (+9.4%), leaching of dissolved total P (+312%), dissolved organic P (+30%), and dissolved inorganic P (+115%), and the ratio of available N to P (+21%). In contrast, soil microbial biomass C (-10%), cellulase activity (-16%), microbial biomass P (-10%), and the ratio of microbial biomass C to nitrogen (-8.1%) significantly decreased under FTC treatments. The likely reason for the increases in soluble soil C and P after FTC is the C and P release from dead soil microorganisms and changes in soil structure enhancing organic matter availability. The mean effect size of FTC generally increased with increasing FTC intensity, which was probably also the main reason for higher responses of soil C and P pools and fluxes to FTC observed in laboratory than in field experiments. However, mean effect sizes of FTC generally decreased with increasing duration and frequency of FTC, very likely due to substrate depletion through microbial uptake and leaching. The results of this meta-analysis contribute to a better understanding of the overall responses of soil C and P pools and fluxes to FTC, providing the basis for more accurate prediction of the impacts of future global climate change on biogeochemical cycles.