Effect of drought on isoprene emission rates from leaves of Quercus virginiana Mill.

Leaf isoprene emission rates (F-iso) were studied in 2-year old trees of live oak (Quercus virginiana Mill.) during two drying-rewatering cycles. During the first drying-rewatering cycle, photosynthesis (A) and stomatal conductance (gs) decreased by 92%(+/- 7%) and 91%(+/- 8%), respectively, while F-iso remained essentially constant for 8 days of treatment. After 12 days under severe drought conditions, F-iso was reduced by 64%(+/- 6%). Similar values were found during the second drying-rewatering cycle. During the recovery phase of both cycles, F-iso recovered more quickly than A and g(s). The lower drought sensitivity of F-iso compared with that of A resulted in a higher percentage of fixed C lost as isoprene (C-iso/C-A) as plants became more stressed, reaching peaks of 50% when A was almost zero. F-iso showed a strong negative linear relationship with pre-dawn leaf water potential (psi(PD)) that could be a useful parameter to include in isoprene emission models to account for effects of drought stress on leaf F-iso. (C) 2004 Elsevier Ltd. All rights reserved.