EFFECT OF MEASUREMENT CO2 CONCENTRATION ON SUGAR MAPLE ROOT RESPIRATION

Accurate estimates of root respiration are crucial to predicting below ground C cycling in forest ecosystems. Inhibition of respiration has b een reported as a short-term response of plant tissue to elevated meas urement [CO2]. We sought to determine if measurement [CO2] affected ro ot respiration in samples from mature sugar maple (Acer saccharum Mars h.) forests and to assess possible errors associated with root respira tion measurements made at [CO2]s lower than that typical of the soil a tmosphere. Root respiration was measured as both CO2 production and O- 2 consumption on excised fine roots (less than or equal to 1.0 mm) at [CO2]s ranging from 350 to > 20,000 mu l l(-1). Root respiration was s ignificantly affected by the [CO2] at which measurements were made for both CO2 production and O-2 consumption. Root respiration was most se nsitive to [CO2] near and below normal soil concentrations (< 1500 mu l l(-1)). Respiration rates changed little at [CO2]s above 3000 mu l l (-1) and were essentially constant above 6000 mu l l(-1) CO2. These fi ndings call into question estimates of root respiration made at or nea r atmospheric [CO2], suggesting that they overestimate actual rates in the soil. Our results indicate that sugar maple root respiration at a tmospheric [CO2] (350 mu l l(-1)) is about 139% of that at soil [CO2]. Although the causal mechanism remains unknown, the increase in root r espiration at low measurement [CO2] is significant and should be accou nted for when estimating or modeling root respiration. Until the direc t effect of [CO2] on root respiration is fully understood, we recommen d making measurements at a [CO2] representative of, or higher than, so il [CO2]. In all cases, the [CO2] at which measurements are made and t he [CO2] typical of the soil atmosphere should be reported.