Carbon efflux rates of fine roots of three tree species decline shortly after excision

Fine roots (diameter 12 mm) of Acer rubrum, Quercus rubra and Pinus strobus were used to determine whether respiration rates (measured as CO2 efflux rates) remain sufficiently stable for the 1 min to 10 h interval after excision to allow reliable measurements to be taken. Roots of five individuals of each species were excavated from the upper 10 cm of the soil. From each tree, two samples of roots (dry weights between 0.21 and 1.18 g) were excised and immediately subjected to one of two treatments. The attached soil was removed mechanically with (wet treatment) or without (dry treatment) the further removal of soil by submersion in and rinsing with water. Within 1 min of excision, roots were placed in a gas exchange system and their respiration was measured. The 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 efflux rates showed a marked decline over time, dropping significantly (p less than or equal to 0.05) over 5 min for Acei and Pinus and over 15 min for Quercus (by 37, 52 and 33%, respectively). The initial rates (12.9, 9.2 and 8.7 nmol CO2 g(-1) s(-1) at 25 degrees C for Acer, Quercus and Pinus, respectively) declined to a minimum (4.2, 2.9 and 4.4 nmol CO2 g(-1) s(-1)) in 30 (Pinus) or 60 (Acer and Quercus) min then levelled off (deer and Quercus) or started to increase (Pinus). Possible mechanisms causing the decline are discussed. (C) 1997 Elsevier Science B.V.