Extreme heat-stress events rapidly alter soil microbial carbon use efficiency and nutrient cycling

This dataset is associated with the paper titled Extreme heat-stress events rapidly alter soil microbial carbon use efficiency and nutrient cycling by Cooledge et al (in review). The abstract is provided below: *** Extreme heat-stress events can disrupt biogeochemical cycling at regional and global scales, leading to devastating environmental and socioeconomic impacts across the agrifood system. Previous studies exploring extreme heat-stress on soil function often apply warming scenarios derived from global surface air temperature projections, where soils are subjected to mean annual temperature increases of 1.5 to 5 °C, rarely exceeding 35 °C. This overlooks the acute temperature extremes where solar-irradiated soil surfaces (0–5 cm) can reach >40 °C, exceeding the thermal optima of most soil microorganisms. This study replicated UK heatwave conditions where soil surface temperature reached 59.7 °C. Using 14C-radioisotope tracing, we determined the effects of heat-stress duration (15-minutes to 7-days), thermal diffusion within the upper soil profile (0-5 cm), and heating method (constant vs. diurnal cycling) on microbial carbon dynamics, carbon use efficiency (CUE), biogeochemistry, and microbial community composition. Total 14C-glucose mineralisation increased 1.5- to 2-fold from 37 ± 1 % in the control (20 °C) to 44-77 % in soils subjected to 59.7 °C for ≥1-hour, with a lag-phase in C cycling occurring within 8-hours of substrate addition. This reduced microbial CUE from 0.61 ± 0.01 (control) to 0.19 ± 0.01 after 2-hours exposure to a thermal extreme. Soil pH and ammonium concentration increased with heat exposure due to cell lysis, alongside a reduction in microbial biomass (from 2.36 to 0.63 g C kg-1) and loss of nitrifiers, with soils dominated by Bacillota. These trends persisted for 14-days, suggesting that exceeding the critical temporal threshold (≥1-hour) creates a lasting soil legacy and a tipping point for microbial activity and nutrient cycling. This was evident by limited microbial recovery when replicating a diurnal heatwave cycle. These results demonstrate the complex effects extreme heat has on soil microbial function, challenging current representations of temperature stress in global soil C models. *** If you have any questions, please contact me via email at [e-mail]