LAUSR

Abstract Microbially-mediated carbon (C) cycling in response to global warming can be simulated by using incubation experiments under varying and/or constant temperature settings. However, the temperature variation influences nutrition utilization pathways and modifies the temperature sensitivity of microbial communities, which challenges the assumptions about the mechanisms underlying microbially-mediated C processes in response to warming under the constant temperature condition. We conducted a 4-month incubation study to test for differences between varying and constant temperature settings in changing the thermal acclimation of microorganisms derived from different forest stands and soil horizons. Under a diurnally varying temperature setting, the Fungal/Gram-negative, Fungal/Gram-positive and Fungal/Actinomycete phospholipid fatty acid (PLFA) ratios increased 17.3%, 23.7% and 47.5%, respectively, from low (10 °C) to high (30 °C) temperature, whereas under constant temperature settings, these ratios increased merely 2.3% or showed marked reductions of 48.0% and 56.5%, respectively, in the high temperature compared to the low temperature. The PLFA stress indicators, such as the ratios of cyclopropyl to monoenoic fatty acids and of Gram-positive to Gram-negative bacteria, significantly increased with warming under the constant temperature settings but did not change or significantly decreased with warming under the varying temperature status. The above distinctions in the microbial community composition between constant and varying temperature regimes were affected by the interactions with the forest stand and with the soil horizon. Our findings suggest that simulations of soil C mineralization in diurnally and seasonally varying temperatures in situ should be carried out in future incubation experiments.