Conventional gas exchange systems adsorb ozone (O3) despite attempts to saturate the system prior to measurements. A steady-state, open photosynthetic system was designed and used in the field to supply a small leaf cuvette with conditioned air stream (growth CO2 concentrations, humidified, cooled) and augmented with either background or elevated O3. Two innovations led to success: (1) supplying the cuvette with cooled air instead of Peltier cooling within the cuvette; and (2) using a custom-designed, low flow (capable of 100 seem), fast response (20 seconds) O3 monitor. We tested whether elevated CO2 would alter stomatal response to short term, steady state elevated O3. Holm oak (Quercus ilex), an evergreen broadleaf tree growing near a geothermal CO2 vent, has been exposed over its lifetime to a gradient of CO2 concentrations. We chose trees in areas averaging 450 µl l-1 (low background CO2) and 1500 µl l-1 (super-elevated CO2). Background O3 exposure at this site is moderate (10 am to 5 pm averages of 62 nl l-1 in June). We measured gas exchange at the growth CO2 levels, and at ambient O3 or 1.7 times ambient O3 concentrations. At low background CO2, short term elevated O3 depressed foliar transpiration. Because there was little concurrent change in net assimilation, instantaneous transpiration efficiency was increased. At super-elevated CO2, short term elevated O3 did not affect foliar transpiration. Because there was a concurrent decrease in net assimilation, instantaneous transpiration efficiency was decreased at elevated CO2 and O3.
A field system to deliver desired O3 concentrations in leaf-level gas exchange measurements: Results for Holm Oak near a CO2 spring.
Paoletti E
2005
Abstract
Conventional gas exchange systems adsorb ozone (O3) despite attempts to saturate the system prior to measurements. A steady-state, open photosynthetic system was designed and used in the field to supply a small leaf cuvette with conditioned air stream (growth CO2 concentrations, humidified, cooled) and augmented with either background or elevated O3. Two innovations led to success: (1) supplying the cuvette with cooled air instead of Peltier cooling within the cuvette; and (2) using a custom-designed, low flow (capable of 100 seem), fast response (20 seconds) O3 monitor. We tested whether elevated CO2 would alter stomatal response to short term, steady state elevated O3. Holm oak (Quercus ilex), an evergreen broadleaf tree growing near a geothermal CO2 vent, has been exposed over its lifetime to a gradient of CO2 concentrations. We chose trees in areas averaging 450 µl l-1 (low background CO2) and 1500 µl l-1 (super-elevated CO2). Background O3 exposure at this site is moderate (10 am to 5 pm averages of 62 nl l-1 in June). We measured gas exchange at the growth CO2 levels, and at ambient O3 or 1.7 times ambient O3 concentrations. At low background CO2, short term elevated O3 depressed foliar transpiration. Because there was little concurrent change in net assimilation, instantaneous transpiration efficiency was increased. At super-elevated CO2, short term elevated O3 did not affect foliar transpiration. Because there was a concurrent decrease in net assimilation, instantaneous transpiration efficiency was decreased at elevated CO2 and O3.I documenti in IRIS sono protetti da copyright e tutti i diritti sono riservati, salvo diversa indicazione.
