Sensitivity of old-field soil respiration to warming and altered precipitation

Background/Question/Methods Soil respiration is the largest terrestrial source of CO₂ to the atmosphere. Soil respiration includes both root and microbial respiration and is sensitive to changes in temperature, moisture and substrate quality. Responses of root respiration to temperature and moisture differ from those of microbial respiration.  We examined the effects of warming and altered precipitation on soil respiration (roots+ microbes) and microbial respiration alone in the old-field community of the Boston Area Climate Experiment at Waltham, MA. The experiment is conducted to evaluate the main and interactive effects of four levels of warming (ambient, +1.3, +2.7, and +4 degrees C) and three levels of precipitation (drought, ambient, wet) on various ecosystem processes. We measured soil respiration monthly in areas where plant roots were present, and excluded. We used data on soil CO₂ efflux and soil temperature at a depth of 5cm to estimate the temperature sensitivity (apparent Q₁₀) of soil respiration in each treatment.  We then analyzed the effects of warming and precipitation change on apparent Q₁₀ in treatments with and without plant roots.  

Results/Conclusions Our initial analyses suggest that both temperature and moisture affected the Q₁₀ of soil respiration (roots+microbes; P<0.05), but that the Q₁₀ of microbial respiration was only affected by moisture (P<0.05). Soil moisture may be more important for microbial respiration because moisture stress affects the free diffusion of soluble carbon substrates and extracellular enzymes that could limit microbial decomposition of organic matter.