The role of stomata in sensitivity of Betula papyrifera seedlings to SO2 at different humidities

Summary Stomata of paper birch (Betula papyrifera Marsh.) seedlings were more open at high humidity than at low humidity and responded rapidly to changes in vapor pressure deficit. SO₂ at 0.2 or 0.8 l l^-1 caused partial stomatal closure. Seedlings fumigated with SO₂ at 0.2 or 0.5 l l^-1 for 30 h or 0.2 l l^-1 for 75 h took up more SO₂ at high than at low humidity. Differences in pollutant uptake could be explained by stomatal conductance with no need to invoke changes in mesophyll conductance. Betula seedlings were more sensitive to SO₂ when fumigated at high humidity, as manifested in more leaf necrosis, increased leaf abscission, and greater growth inhibition compared to seedlings fumigated at low humidity. Amount of injury to leaves increased with rate of SO₂ uptake, and inhibition of root growth increased with total SO₂ uptake.Abbreviations RH relative humidity - VPD vapor pressure deficit - RGR mean relative growth rate - PPFD photosynthetic photon flux density (400–700 nm) - LDC leaf diffusive conductance - water potentialResearch supported by the College of Agricultural and Life Sciences, University of Wisconsin-Madison