Environmental control of stomatal conductance in forest trees of the GreatSmoky Mountains National Park

To determine if stomatal conductance (g(s)) of forest trees could be predic ted from measures of leaf microclimate, diurnal variability in in situ g(s) was measured in black cherry (Prunus serotina), red maple (Acer rubrum), a nd northern red oak (Quercus rubra). Relative to overstory trees, understor y saplings exhibited little diurnal variability in g(s) and ozone uptake. D epending on species and site, up to 30% of diurnal and seasonal variation i n g(s) of overstory trees was explained by photosynthetically active radiat ion and vapor pressure deficit. Daily maximum g(s) was significantly relate d to soil moisture in overstory northern red oak and black cherry (R-2 rang ed from 33 to 65%). Although g(s) was not fully predicted using instantaneo us measures of leaf microclimate, ozone uptake of large forest trees was re duced by low soil moisture. (C) 2000 Elsevier Science Ltd. All rights reser ved.