Changing soil available substrate primarily caused by fertilization management contributed more to soil respiration temperature sensitivity than microbial community thermal adaptation

Abstract

Substrate depletion and microbial community thermal adaptation are major mechanisms that regulate the temperature sensitivity (Q₁₀) of soil microbial respiration. Traditionally, the Q₁₀ of soil microbial respiration is measured using laboratory incubation, which has limits in the continuous input of available substrates and the time scale for microbial community thermal adaptation. How the available substrate and the soil microbial community regulate the Q₁₀ of soil microbial respiration under natural warming conditions remains unclear. To fill this gap in knowledge, a long-term field experiment was conducted consisting of two years of soil respiration observations combined with a soil available substrate and microbial community thermal adaptation analysis under seasonal warming conditions. The Q₁₀ of soil respiration was calculated using the square root method, and it was more affected by the available substrate than by microbial community thermal adaptation. Fertilization management has a stronger effect on soil available substrate than temperature. As the temperature increased, NH₄-N proved itself to be important for the bacterial community in the process of Q₁₀ regulation, while dissolved organic carbon and nitrogen were key factors for the fungal community. Based on the niche breadth of microbial community composition, the changing Q₁₀ of the soil respiration was not only closely associated with the specialist community, but also the generalist and neutralist communities. Furthermore, bacterial community thermal adaptation primarily occurred through shifts in the abundances of specialists and neutralists, while changes in species richness and species replacement occurred for the fungal generalists and neutralists. This work indicates that changing available nitrogen and DOC primarily caused by fertilization management contributed more in regulating the Q₁₀ of soil microbial respiration than microbial community thermal adaptation, and there are different mechanisms for bacterial and fungal community thermal adaptation under warming.

Keywords: Available nitrogen; Dissolved organic carbon; Microbial community thermal adaptation; Q(10) of soil respiration; Soil respiration.