PNNL

Abstract

Microbial response to changing environmental factors influence 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 occur 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 rewet. Using these differentiated 12CO2 and 13CO2 respiration rates soils after rewet, we were able to deduce when microbes are accessing different pools of carbon. Immediately upon rewet, respiration of 12CO2 occurred first, with negligible 13CO2 respiration. Appreciable metabolism and respiration of the added 13C glucose did not occur until 15 minutes after rewet. We conclude that while all carbon pools are being accessed in the first 9 hours after rewet, the rate and timing that new and existing carbon pools are being accessed varies. Discerning which carbon pools are metabolized first is vital to understanding how microorganisms will respond to the perturbations and how carbon metabolism can further affect climate, carbon sequestration, and soil health.