Feedbacks between warming and temperature sensitivity of soil respiration: Theoretical considerations of the mechanisms
The feedback between warming and soil respiration remains the largest uncertainty in an accurate prediction of future climate and global carbon cycle. Investigating how temperature sensitivity of soil respiration changes in a warming world is critical in understanding such feedback. Through lab incubation, field measurement and analysis of data from published literature, we have observed a tendency of decreasing relative temperature sensitivity in response to warming. However, mechanisms behind these observations have not been throughly investigated and compared. Here, we use general formulation to model soil respiration and explore potential mechanisms from a theoretical perspective to investigate 1) plausible mechanisms that generate such observation and 2) conditions under which such observation is more likely to be observed.
We explore two broad categories of possible mechanisms: thermodynamics of chemical reactions, and microbial physiological or community response. Considering mechanisms related to the thermodynamics of chemical reaction, we demonstrate that the changes in composition of kinetically distinct substrates is a plausible mechanism behind the observed decrease in temperature sensitivity. Conditions under which the thermodynamics generate the observation is in general agreement with existing literatures. Considering microbe related mechanisms, we demonstrate how the direction and magnitude of changes in the key physiological traits, such as mass specific respiration rate and allocation strategy, and population/community level responses, such as total biomass and community composition, could lead to the observed changes in temperature sensitivity. Our analysis and comparison provide a useful guidance for experimental design and data interpretation to link temperature sensitivity of soil respiration to its underlying mechanisms.