Warming yields distinct accumulation patterns of microbial residues in dry and wet alpine grasslands on the Qinghai-Tibetan Plateau

High altitude alpine grasslands in the Qinghai-Tibetan Plateau (QTP) contain high soil organic C (SOC) stocks that are extremely vulnerable to climate warming. Microbial residues are increasingly recognized as a major source of SOC, however, how climate warming affects this component of SOC in this region remains largely unknown. In this study, we examined the response of microbial residues to a 3-year experimental warming and the degree to which they contributed to SOC storage in two Tibetan ecosystems-alpine steppe (AS) and swamp meadow (SM). The number of microbial residues was indicated by amino sugar analysis. Our results revealed that warming yielded divergent microbial residue accumulation that significantly altered their contribution to SOC storage in the two alpine grasslands. Warming increased microbial residue abundance by approximately 17.6% across 0 to 20 cm depth in SM soils, while causing a significant decline (about 6.2%) in AS soils. The higher microbial residue accumulation in SM could lessen potential positive feedbacks from climate warming, while the decrease in microbial residues in AS may indicate greater loss of microbial-derived C inputs in warmed soils. Moreover, we found that warming selectively increased fungal residues as compared with bacterial despite inconsistent responses to warming in the two grasslands. These changes were accompanied by significant shifts in fungal to bacterial residue C ratios and their contribution to SOC pool, indicating an alteration of SOC composition and stability in alpine grassland ecosystems. These findings demonstrate that a microbial-derived C feedback to climate change is ecosystem-specific that alters the direction and magnitude of the microbial community.