Microbial Diversity Losses Constrain the Capacity of Soils to Mitigate Climate Change.

Soil microbes may adapt to climate warming, potentially reducing the warming-induced increase in microbial carbon emissions such as carbon dioxide, and thereby helping to mitigate climate change. Yet, soil microbes are subjected to various global change stresses (e.g., warming, drought, flooding, and land-use changes), altering their biodiversity, which challenges microbial adaptation to climate change. Here, we created microbial diversity gradients in microcosms at two different temperatures using soils from a 2000-km field survey. We found that reduced microbial diversity weakens the thermal adaptation of soil microbial respiration and can further enhance the microbial respiratory temperature sensitivity over time. Our analyses further revealed that the negative impact of microbial diversity losses is linked to the decline of keystone microbial taxa, which can adapt to temperature changes and are crucial for the community's ability to compensate for the temperature-driven effects on soil respiration in the long term. Taken together, our study provides new insights into the key role of microbial diversity in driving the thermal response of soil heterotrophic respiration, suggesting that any global change-driven shifts in microbial diversity can have critical consequences for the future of carbon stocks.