Fine root respiration in mature eastern white pine (Pinus strobus) in situ: the importance of CO2 in controlled environments

We measured seasonal fine root respiration rate in situ while controlling c hamber temperature and [CO2]. Atmospheric [CO2] ([CO2](a)) and measured soi l [CO2] ([CO2](s)) were alternately delivered to a cuvette containing intac t fine roots of eastern white pine (Pinus strobus L.). Respiration rates we re consistently higher in [CO2](a) than in [CO2](s) and were almost three t imes higher during midsummer. Respiration rates were immediately reversed a fter returning to the alternate [CO2] (i.e., [CO2](a) --> [CO2](s) --> [CO2 ](a), and vice versa) suggesting a direct effect of elevated [CO2] on appar ent respiration. Soil-[CO2]-based respiration rates decreased with increasi ng [CO2] on a dry mass and tissue [N] basis. We conclude that estimates of soil CO2 flux and soil carbon budgets may be improved by more completely ac counting for the rhizosphere microclimate (i.e., soil temperature and [CO2] (s)) during measurement of fine root respiration.