CARBON EFFLUX RATES OF FINE ROOTS OF 3 TREE SPECIES DECLINE SHORTLY AFTER EXCISION

Fine roots (diameter 12 mm) of Acer rubrum, Quercus rubra and Pinus st robus were used to determine whether respiration rates (measured as CO 2 efflux rates) remain sufficiently stable for the 1 min to 10 h inter val after excision to allow reliable measurements to be taken. Roots o f five individuals of each species were excavated from the upper 10 cm of the soil. From each tree, two samples of roots (dry weights betwee n 0.21 and 1.18 g) were excised and immediately subjected to one of tw o treatments. The attached soil was removed mechanically with (wet tre atment) or without (dry treatment) the further removal of soil by subm ersion in and rinsing with water. Within 1 min of excision, roots were placed in a gas exchange system and their respiration was measured. T he measurements were repeated 5, 15, 30 min and 1, 2 (Acer and Pinus), 3 (Quercus), 6 and 10 h after excision. For all species, carbon efflu x rates showed a marked decline over time, dropping significantly (p l ess than or equal to 0.05) over 5 min for Acei and Pinus and over 15 m in for Quercus (by 37, 52 and 33%, respectively). The initial rates (1 2.9, 9.2 and 8.7 nmol CO2 g(-1) s(-1) at 25 degrees C for Acer, Quercu s and Pinus, respectively) declined to a minimum (4.2, 2.9 and 4.4 nmo l CO2 g(-1) s(-1)) in 30 (Pinus) or 60 (Acer and Quercus) min then lev elled off (deer and Quercus) or started to increase (Pinus). Possible mechanisms causing the decline are discussed. (C) 1997 Elsevier Scienc e B.V.