Release of Carbon and Nitrogen from Alpine Soils During Thawing Periods in the Eastern Qinghai-Tibet Plateau

Abstract

Soil thawing can affect the turnover of soil carbon (C) and nitrogen (N) and their release into the atmosphere. However, little has been known about the release of C and N during the thawing of alpine soils in the Qinghai-Tibet Plateau. This study investigated the effects of soil thawing on the release of CO2, CH4, and N2O from alpine peatland soils and alpine meadow soils through an indoor experiment and determined the changes in the dissolved organic C (DOC), dissolved organic N (DON), NO3--N, NH4+-N, and NO2--N concentrations in the soils after soil thawing. The freeze-thaw treatments were performed by incubating the soil columns at mild (-5 degrees C) and severe (-15 degrees C) for 14 days, and then at 5 degrees C for 18 days. The control columns were incubated at 5 degrees C. During thawing, the cumulative CO2 emissions from the severely frozen alpine peatland soils and alpine meadow soils were 36 and 85 % higher than those from the control soils, and the cumulative N2O emissions were 3.9 and 5.8 times higher than those from the control soils. However, the thawing after mild freezing produced no significant effects. The two freezing temperatures significantly increased the release of CH4 from the alpine peatland soils, but the thawing of the severely frozen soils reduced the CH4 uptake of the alpine meadow soils by 27 %. After the severely frozen alpine peatland soils thawed, the concentrations of DOC, DON, NO3--N, NH4+-N, and NO2--N increased significantly, but NO2--N showed no significant changes for the alpine meadow soils. After thawing with mild freezing, DOC in the alpine peatland soils and NH4+-N, NO2--N, and DOC in the alpine meadow soils showed no significant changes. This study indicates that the potential for release of C and N from alpine soils during thawing periods strongly depends on the freezing temperature and soil types.