Document: MAA-3-30-27

The effects of leaf wetness on photosynthesis of and ozone deposition to Poplar leaves.

SCHREUDER, M.D.J.* ¹, L.W.A.VAN HOVE ² and C.A.BREWER ¹

University of Montana, Missoula, MT 59812 ¹
Wageningen University and Research Center ²

Abstract:
Leaf wetness events such as dew, rain and mist are common in field conditions, and affect gas exchange over leaf surfaces. We examined the effects of leaf wetness on photosynthesis of and ozone deposition to Populus nigra brandaris leaves. Photosynthesis, transpiration and ozone deposition were monitored in light (PAR 420 7 SE umol m ^-2 s^-1) and dark conditions, and leaves were sprayed with deionized water, and simulated acid rain and mist, with pH 7.0, 4.5 and 3.7 respectively. Background ozone concentrations in the cuvettes averaged 102 1 SE ug O₃ m^-3. During light conditions leaf wetness decreased net photosynthesis by 16 % (p<0.001). Dark respiration decreased by 60, 82 and 100 % using water with pH 7.0, 4.5 and 3.7 respectively (p<0.001). Net photosynthesis and ozone deposition were highly correlated (r²=0.98, p<0.0001). In light conditions leaf wetness increased ozone deposition by a factor of 1.1, lasting 30 minutes on average. In darkness leaf wetness increased ozone deposition 2.7 to 3.4 times, 160 minutes on average, and effects decreased with lower pH. Ozone deposition to wet leaves in light conditions could be explained by: 1) decreased deposition due to lower stomatal conductance, and 2) increased deposition into the water film (r²=0.86, p<0.001). Thus, leaf wetness and water pH significantly altered CO₂ gas exchange and ozone deposition, especially at night. These factors need to be incorporated in ozone deposition models.

Keywords: photosynthesis, ozone deposition, leaf wetness, acid precipitationis

This abstract is being presented at: 2:00 PM in session:
Oral Session #50: Plant Gas Exchange.