The Effect of Warming and Simulated Rainfall on Soil Microbial Community Structure and Function

Soil respiration, from plant roots and soil microbes, accounts for 60 – 80 percent of total ecosystem respiration, with the microbial component contributing approximately 54 percent. Global climate trends resulting from CO2 emissions include increased soil temperatures and changes in precipitation regimes resulting in less frequent, more intense rainfall events. Soil temperature and moisture availability drive soil respiration rates, but how they impact the microbial respiration is poorly qualified. I investigated how the soil microbial community responds to changes in temperature and moisture availability in a laboratory based experiment. Soils from a mixed hardwood forest under two thermal regimes received either a large or small simulated rainfall event. A large event corresponded with the highest recorded daily average rainfall event for a 30 year period and a small event was half that amount. Soil temperature, moisture, and respiration were measured at 30 minute intervals for the duration of the experiment. I used the following metrics to quantify microbial respiratory respoinse: (1) maximum rate of soil microbial respiration (SMRmax); (2) the amount of time it took to reach SMRmax (Tmax); (3) the amount of time it took to return to pre-rainfall rates of soil microbial respiration (Tduration); and the total CO2 production in each mesocosm associated with rainfall (SMRtotal). Temperature treatments positively influenced SMRmax, but had no impact on my other metrics. Rainfall event size positively impacted SMRmax, Tduration, and SMRtotal. My research suggests that in temperate mixed hardwood forest soils moisture is a stronger driver of soil microbial respiration than temperature