PS 7-59
Sugar maple fine-root respiration is mechanistically constrained by adenylate control after 3 years of experimental soil warming
The response of plant tissue respiration to climatic warming can influence both return of assimilated C to the atmosphere and net primary productivity. We have previously shown that root respiration in sugar maple can partially acclimate to warmer soil, avoiding excessive respiratory C loss and presumably aligning root C use with the work required of the root system for acquisition of resources. This study investigated two potential mechanisms for this acclimation. This study was conducted at the sugar maple soil warming experiment in Michigan. Treatments include a fully factorial combination of soil warming (ambient, +5 oC), and moisture addition, (ambient, 1.3x ambient growing season). We used applications of exogenous sugar to test for substrate limitation of respiration and a decoupling agent (carbonyl cyanide m-chlorophenylhydrazone, CCCP) to test for adenylate control. CCCP dissipates the H+ gradient of the mitochondria and allows respiration to proceed without production of ATP, eliminating reductions in respiration associated with low levels of ADP that could occur when ATP production exceeds cell metabolic requirements. Surface fine-roots (<1 mm) from all treatments were immersed in glucose and/or CCCP for 15 minutes then respiration measured with an infrared gas analyzer at three times during 2013.
Results/Conclusions
There was evidence of temperature acclimation of fine-root respiration as indicated by less respiration on the heated plots at common reference temperature of 18 oC, as has occurred consistently from 2010-2013 (P < 0.001, n = 26 dates). Glucose additions had no effect on fine-root respiration (P = 0.94) indicating that substrate limitation was not constraining respiration. The CCCP application increased fine-root respiration for all treatments (P < 0.001); indicating some degree of adenylate control was present in all cases. However, CCCP caused greater relative enhancement of respiration for roots from heated soil (P = 0.10) when compared to the controls. The greater relative increase in respiration after CCCP additions to roots from heated soil suggests that fine-root respiration in these treatments is being down-regulated to match the work required of the root system for nutrient uptake and assimilation.