Variations in soil aggregate stability and organic carbon stability of alpine meadow and shrubland under long-term warming

Global warming is increasingly impacting the structure and functioning of the ecosystems in the Tibetan plateau. However, information about warming effects on the stability of carbon pools in soil aggregates is limited. Here, we implemented a 21-year long-term open-top-chamber (OTCs) warming experiment to reveal the warming effects on the stability of topsoil aggregate structure and carbon pools in a Tibetan alpine meadow and shrubland. The results demonstrated that long-term warming significantly reduced the soil aggregate stability of the shrubland, but had no significant effect on the alpine meadow. Although warming enhanced the stability of carbon pools in topsoil aggregate fractions for both the alpine meadow and shrubland, a negative response of the carbon management index (CMI) and carbon pool storage in the alpine meadow was found, while shrubland showed a positive response to warming. The response of carbon fractions to warming depended on soil aggregate size, with a reduction of labile C fraction 1 (C1) and stable carbon fraction (C4) in large (LMGA: >2 mm) and small macroaggregates (SMGA: 2–0.25 mm) of the alpine meadow, and unchanged carbon fractions in microaggregates (MIGA: <0.25 mm) for both the alpine meadow and shrubland. Long-term warming significantly decreased C-acquiring enzyme activity in shrubland, but had no significant effect on the meadow. Enzyme activity and glomalin-related soil protein (GRSP) concentration decreased as the size of soil aggregates increased in the alpine meadow and shrubland, which could be attributed to the structural characteristics of microaggregates, which have larger specific surface area and stronger microbial protection ability. Our findings provide a new perspective in understanding the response of alpine meadow and shrubland soil structure and carbon pool stability to long-term warming at the soil aggregate level.