Purpose Global climate change scenarios forecast the increasing frequency of extreme precipitation events in the Qinghai-Tibet Plateau (QTP), events that likely will result in increased annual rainfall. The effects of varying rainfall frequency on terrestrial ecosystems, especially in QTP regions impacted by global warming, have become a major research topic. However, the responses of soil labile organic carbon fractions to different rainfall frequencies in the QTP remain unknown. Methods In this study, we set five rainfall frequencies in the wet meadows of the QTP (control plots, CK; once a week, DF1; once every 2 weeks, DF2; once every 3 weeks, DF3; and once every 4 weeks, DF4). Rainfall frequency treatments received monthly ambient rainfall plus 25 mm of additional rainfall for each irrigation event, and the number of irrigation events was varied. The soil organic carbon fractions (soil organic carbon, SOC; microbial biomass carbon, MBC; and dissolved organic carbon, DOC) in the 0-10, 10-20, and 20-40 cm soil layers were determined. Results We identified significant relationships of soil carbon fractions. With increased rainfall frequency, SOC content increased significantly and DOC content decreased significantly (P < 0.05). The MBC contents of DF3 were 25.1% (0-10 cm) and 32.14% (10-20 cm) higher than that of CK. During the plant growth season, soil carbon components had different patterns over time. The maximum SOC content was recorded in August, and the maximum soil DOC content was recorded in June or July. The minimum content of MBC was observed in July. Conclusion Our results show that the low frequency of extreme rainfall events increased microbial activity and promoted the decomposition of SOC, which was not conducive to the accumulation of soil carbon.
