Do soil microbes adapt to warming?

<p>Climate warming may be exacerbated if rising temperatures stimulate losses of soil carbon to the atmosphere. Despite a plethora of studies stimulated by this alarming perspective, the direction and magnitude of this so-called carbon-climate feedback remain uncertain. Part of the uncertainty is due to lack of knowledge of the thermal adaptation of the physiology and composition of soil microbial communities. Here, we tested the hypothesis that microbial communities adapt to long-term warming with a shift in their composition and their temperature response that are consistent with evolutionary theory. We used the unique combination of state-of-the-art macromolecular rate theory (MMRT) to describe the temperature response of microbial respiration and metabarcoding to characterise the microbial community composition of soils sampled along transects of increasing distance from a geothermally active zone in New Zealand. Along those transects, the mean annual temperature of the soil increased dramatically (by up to 15^oC), and this concurred with shifts in microbial communities composition, with thermophile and thermotolerant genera increasing in relative abundance with increasing ambient temperature. However, the ambient temperature had no detectable influence on the MMRT parameters or the relative temperature sensitivity of decomposition (<em>Q</em>₁₀). MMRT parameters were, however, strongly correlated with soil carbon concentration and carbon:nitrogen ratio. Our findings suggest that, while long-term warming selects for warm-adapted taxa, substrate quality and quantity exert a stronger influence than temperature in selecting for distinct thermal traits. The results have major implications for our understanding of the role of soil microbial processes in the long-term effects of climate warming on soil carbon dynamics and will help increase confidence carbon-climate feedback projections.</p>