Aerosol deposition increases conductance to water in immobilized stomata closed with abscisic acid or opened with fusicoccin

Hypothesized effects of aerosol deposition on plant water balance have been difficult to establish. This is due to variability between species, stomatal response to the treatment itself, and to environmental effects. Here we attempt a quantitative evaluation with a defined aerosol application, a paired leaf experimental design, and immobilized stomata. Attached leaves of poplar were treated with ammonium nitrate aerosol. After 17 or 20 days for deliquescence to develop an aqueous film, leaves were excised and stomata held closed with abscisic acid or open with fusicoccin. Transpiration and stomatal conductance were measured in a greenhouse with a porometer and leaf health was assessed by fluorescence. Median stomatal conductance was increased significantly, by 60 and 65%, following aerosol loading of 31.3 g cm-2 in ABA- and FC-treated leaves, respectively. Aerosol induced transpiration, probably associated with a liquid film that lines the stomatal pore and not effectively regulated by stomatal closure, may be significant in magnitude. As aerosol deposition is ubiquitous, and its chemical nature may be changing, this factor should be considered in models of transpiration from leaf to canopy scale.