Effects of long-term warming on microbial nutrient limitation of soil aggregates on the Qinghai-Tibet Plateau

Background and aims Global warming has increasingly serious impacts on the structure and function of the Tibetan Plateau ecosystem. However, the mechanism by which warming affects the biogeochemical processes, and consequently the microbial nutrient limitation in soil aggregates, is not clear. Methods In the present study, we used open-top chamber experiments to simulate warming in an alpine meadow and an alpine shrubland on the Qinghai-Tibet Plateau, and we measured the C, N, and P-acquiring enzyme (β-1, 4-glucosidase, BG; leucine aminopeptidase, LAP; β-N-acetylglucosaminidase, NAG; alkali phosphatase, AP) activities and their stoichiometry to understand how warming affects microorganism-limiting mechanisms in soil aggregates. Results The results showed that long-term warming treatment significantly decreased soil organic carbon (SOC) and total nitrogen (TN) concentrations of large macroaggregates (LMGA) and small macroaggregates (SMGA) in alpine meadows, but significantly increased SOC concentration of LMGA in alpine shrubland. The SOC and TN concentrations of alpine meadows increased with the decrease of soil aggregate size and the concentrations in microaggregate (MIGA) were significantly higher than those LMGA. Soil enzyme activity increased with the decrease in aggregate size and was not significantly affected by warming treatment. Enzyme stoichiometry results demonstrated that soil microbes in alpine meadows and shrubland were limited by nutrient P relative to nitrogen; moreover, the long-term warming treatment aggravated the P limitation of soil microorganisms in the shrubland, and it had significant differences in LMGA and MIGA. At the same time, the long-term warming treatment had no significant effect on C limitation in the alpine shrubland and alpine meadows, but soil aggregate size affected the C limitation patterns of microorganisms and showed the greatest limitations in MIGA. Conclusions The microbial P limitation in shrubland is more sensitive to warming than that in meadow. Soil aggregates mediate the acquisition of C by microorganisms, and the C limitation in MIGA is the greatest. By providing a new perspective on this topic, our study increased our understanding of the effects of warming on microbial nutrient utilization and restriction patterns in soil aggregates.

Effects of Long-Term Warming on Microbial Nutrient Limitation of Soil Aggregates on the Qinghai-Tibet Plateau

Background and aims Global warming has increasingly serious impacts on the structure and function of the Tibetan Plateau ecosystem. However, the mechanism by which warming affects the biogeochemical processes and consequently the microbial nutrient limitation in soil aggregates is not clear. Methods In the present study, we used open-top chamber experiments to simulate warming in an alpine meadow and an alpine shrubland on the Qinghai-Tibet Plateau to understand how warming affects nutrient utilization and microorganism-limiting mechanisms in soil aggregates. Results The results showed that long-term warming treatment had contrasting effects on soil organic carbon (SOC) content of the alpine meadow and that of the shrubland. This difference was more pronounced with the increase in soil aggregate size, and the SOC content in microaggregates (MIGA) was significantly higher than that in large macroaggregates (LMGA). Soil enzyme activity increased with the decrease in aggregate size and was not significantly affected by warming treatment. Enzyme stoichiometry demonstrated that microbial P limitation is widespread on the Tibetan Plateau, and the long-term warming treatment exacerbated it, which has significant differences in shrubland. At the same time, the long-term warming treatment had no significant effect on C limitation in the alpine shrubland and the alpine meadow, but soil aggregate size affected the C limitation patterns of microorganisms and showed strong limitations in MIGA. Conclusions The microbial P limitation in shrubland is more sensitive to warming than that of grassland. Soil aggregates mediate the acquisition of carbon by microorganisms, and the carbon limitation in MIGA is the greatest. By providing a new perspective on this topic, our study increased our understanding of the effects of warming on microbial nutrient utilization and restriction patterns in soil aggregates.