Soil properties mediate the freeze-thaw-related soil N2O and CO2 emissions from temperate grasslands

Abstract

Freeze-thaw cycles (FTCs) may affect soil carbon (C) and nitrogen (N) cycling and thus stimulate greenhouse gas emissions in cold regions. However, the dynamics of these gases in response to FTCs, especially for N2O, vary substantially due to the differences in soil properties. We conducted an incubation study to investigate the effects of soil properties from different land cover types (arid steppe, AS; typical steppe, TS; meadow steppe, MS; and marshland, ML) on the N2O and CO2 emissions during three FTCs from temperate grasslands in Northeast China. Our results showed that the freeze-thaw-related soil N2O and CO2 emissions differ significantly among different land cover types. Significant increases in N2O emissions during FTCs were observed from the MS, ML, and TS soils, but not from AS soils, which indicated that threshold values of some key soil properties might exist triggering N2O pulse emissions during thawing. Furthermore, AS soil cores were amended with deionized water, glucose-C and NO3−-N, respectively, to identify the crucial factors for N2O emissions during FTCs. The significantly increased N2O emissions from AS soils after amendments with water and/or nutrients confirmed that soil organic carbon (SOC), NO3− and water content might be the limiting factors influencing the N2O emissions from AS soils during FTCs. In addition to soil substrates and moisture, our results suggest that the soil texture and bulk density significantly impact N2O and CO2 emissions during FTCs. Stepwise multiple regression analysis showed that TN coupled with the soil WFPS and sand content could explain 95% of the spatial variability in N2O fluxes, and 75% of the variations in CO2 fluxes were related to the SOC and clay contents. Thus, our results indicate that the interactions between soil properties and FTCs in various ecosystems are important for predicting regional and global greenhouse gas balances, especially in cold regions.