Effects of extreme rainfall frequency on soil organic carbon fractions and carbon pool in a wet meadow on the Qinghai-Tibet Plateau

The frequent occurrence of extreme rainfall events may greatly affect soil organic carbon (SOC) fractions and carbon (C) pool of wet meadow in the Qinghai-Tibet Plateau (QTP). However, it remains unclear how SOC fractions will change under different extreme rainfall frequency. Therefore, we set five extreme rainfall fre-quency treatments in the QTP wet meadow: CK (control plots), DF1 (once a week), DF2 (once every-two weeks), DF3 (once every-three weeks), DF4 (once every-four weeks), all treatments received ambient rainfall. We found that soil particulate organic carbon (POC) content increased with the increasing of extreme rainfall frequency in 0-40 cm layer. Extreme rainfall frequency significantly decreased dissolved organic carbon (DOC) content in 0-10 cm layer. DF2, DF3 and DF4 significantly decreased the soil easily oxidizable carbon (EOC) content, DF2 significantly increased and DF4 significantly decreased SOC content in 0-10 cm layer. Soil organic carbon storage (SOCS) decreased with the increase of extreme rainfall frequency, the lowest value in DF1 treatment (85.61 mg.hm(-2)) and the highest value in DF4 treatment (139.92 mg.hm(-2)). The EOC/SOC and DOC/SOC values at 20-40 cm were greater than those at 0-10 cm under each treatment, and the proportion of SOC fractions in the surface layer (0-10 cm) was more sensitive to the extreme rainfall frequency, while in the deep soil layer (10-20, 20-40 cm) was relatively stable. Redundancy analysis (RDA) showed that soil bulk density (BD) (Explanation = 31.8 %), total phosphorus (TP) (Explanation = 12.8 %), NH4+-N (Explanation = 8.8 %) were important envi-ronmental factors affecting the SOC fractions content under extreme rainfall frequency. Our study suggests that the increase of extreme rainfall frequency in the future will lead to significant differences in the content of SOC fractions and will reduce the SOCS by affecting soil physicochemical properties, and this may have a serious impact on the C sequestration function and C pool stability of QTP wet meadow soil.