Interaction of drought and ozone exposure on isoprene emission from extensively cultivated poplar

摘要

The combined effects of ozone (O-3) and drought on isoprene emission were studied for the first time. Young hybrid poplars (clone 546, Populus deltoides cv. 55/56 x P. deltoides cv. Imperial) were exposed to O-3 (charcoal-filtered air, CF, and non-filtered air +40 ppb, E-O-3) and soil water stress (well-watered, WW, and mild drought, MD, one-third irrigation) for 96 days. Consistent with light-saturated photosynthesis (Asat), intercellular CO2 concentration (Ci) and chlorophyll content, isoprene emission depended on drought, O-3, leaf position and sampling time. Drought stimulated emission (+38.4%), and O-3 decreased it (-40.4%). Ozone increased the carbon cost per unit of isoprene emission. Ozone and drought effects were stronger in middle leaves (13th-15th from the apex) than in upper leaves (6th-8th). Only Asat showed a significant interaction between O-3 and drought. When the responses were up-scaled to the entire-plant level, however, drought effects on total leaf area translated into around twice higher emission from WW plants in clean air than in E-O-3. Our results suggest that direct effects on plant emission rates and changes in total leaf area may affect isoprene emission from intensively cultivated hybrid poplar under combined MD and O-3 exposure, with important feedbacks for air quality.