Impact of experimental soil warming, snow addition, and grazing on soil microbial community diversity and functional potential in Tibetan Kobresia grasslands

Temperature on the Tibetan Plateau (TP) is rising at a rate higher than the global average, and the frequency of extreme climate events is predicted to increase, making the TP a region of critical importance for understanding the consequences of climate change on ecosystems and its feedbacks. The TP hosts the largest alpine pastoral ecosystem in the world: the Kobresia grasslands, dominated by the sedge species Kobresia pygmaea. These ecosystems store most of the terrestrial carbon (C) on the plateau, primarily in the felty root mat. With continuous warming, the carbon captured by Kobresia grasslands may become increasingly vulnerable to decomposition. Our study, therefore, focuses on the soil microbial community’s response to long-term exposure to warming, grazing, and snow addition in a Tibetan alpine pasture, thus reflecting major environmental changes.

We conducted our study at the Nam Co Observation and Research Station for Multisphere, CAS. The fully factorial experiment includes a combination of treatments: warming using open-top chambers, grazing by yaks three times a year (June, July, and August), and spring snow addition using snow cakes measuring 1 m in diameter and 0.5 m in height. Bulk and rhizosphere soil samples were collected for bacterial (16S rRNA) and fungal (ITS1 rRNA) sequencing. Functional genes involved in the carbon (C), nitrogen (N), phosphorus (P), and sulfur (S) cycles were quantified using the high-throughput quantitative-PCR-based Quantitative Microbial Elemental Cycling chip.

Results showed no significant effects of the treatments on microbial fungal or bacterial diversity, community composition, structure, or functional potential for bulk soils. Rhizosphere soils exhibited higher bacterial diversity from plots with warming + grazing treatment. Furthermore, the abundance of genes related to microbial functional potential for C and P degradation was significantly higher in rhizosphere soil than in the bulk soil. Samples from the plots subjected to both warming and grazing treatments showed a higher relative abundance of predominant genes. These findings suggest that the synergistic effects of warming and grazing significantly enhance rhizosphere microbial diversity and functional potential compared to individual treatments, highlighting the complex interactive effects of environmental factors on soil microbial communities.