Real-Time and Rapid Respiratory Response of the Soil Microbiome to Moisture Shifts

Microbial response to changing environmental factors influences the fate of soil organic carbon, and drought has been shown to affect microbial metabolism and respiration. We hypothesized that the access of microbes to different carbon pools in response to dry-rewet events occurs sequentially at different rates. We amended desiccated soils with ¹³C-labeled glucose and measured the rates of ¹²CO₂ and ¹³CO₂ respiration in real time after rewetting. Using these differentiated ¹²CO₂ and ¹³CO₂ respiration rate soils after rewetting, we were able to deduce when microbes are accessing different pools of carbon. Immediately upon rewetting, respiration of ¹²CO₂ occurred first, with negligible ¹³CO₂ respiration. Appreciable metabolism and respiration of the added ¹³C glucose did not occur until 15 min after rewetting. We conclude that, while all carbon pools are being accessed in the first 9 h after rewetting, the rate and timing at which new and existing carbon pools are being accessed varies. Within this study, using stable isotope-labeled substrates to discern which carbon pools are metabolized first uniquely illustrates how microorganisms access different carbon pools which has implications into understanding how carbon metabolism can further affect climate, carbon sequestration, and soil health.