DROUGHT REDUCES ROOT RESPIRATION IN SUGAR MAPLE FORESTS

Soil moisture deficits can reduce root respiration, but the effects ha ve yet to be quantified at the stand level or included in models of fo rest carbon budgets. We studied fine-root (less than or equal to 1.0 m m diameter) respiration in four sugar maple forests for three growing seasons in order to assess the combined effects of temperature, N conc entration, and soil moisture on respiration rates. Fine-root respirati on at the four sites was exponentially related to soil temperature and linearly related to root N concentration and soil moisture availabili ty. Most of the variability in respiration rates was explained by temp erature. Differences in soil moisture availability explained temporal variation within sites in respiration rate at a given temperature, whe reas differences among sites in respiration rates resulted from site-s pecific differences in fine-root N concentration. Periodic moisture de ficits during 1995 and 1996 were sufficient to cause declines of up to 17% in total growing-season root respiration at affected sites. Estim ated reductions in respiration of up to 0.8 Mg C/ha during dry years w ere equivalent to a significant portion of annual aboveground woody bi omass C increment, arguing for the inclusion of soil moisture availabi lity as a predictor of root respiration when modeling C allocation in forest ecosystems.