Abscisic acid synthesis in Acer rubrum L. leaves -: A vapor-pressure-deficit-mediated response

Quantitative differences in leaf abscisic acid (ABA) among Acer rubrum L. (red maple) ecotypes were investigated. This study tested the hypothesis that seedlings from wet and dry maternal sites display distinctly different capacities to synthesize ABA in response to atmospheric vapor pressure deficits. The increased levels of ABA in leaf tissue in the red maple ecotypes were associated with atmospheric vapor pressure deficit (VPD). Leaves on well-watered plants responded to VPD by increasing their ABA levels and reducing their photosynthesis (A(net)) and stomatal conductance (g(s)). Both ecotypes appear to accumulate ABA at about the same rate as VPD increased. Despite the similar accumulation rates between ecotypes, wet site ecotypes consistently had a higher level of ABA present in leaf tissue under both-low and high VPD conditions. Furthermore, wet site provenances appear to reduce A(net) and g(s) in response to ABA accumulation, whereas dry sites do not present as clear an ABA/g(s) relationship. This study shows variation between wet and dry site red maple populations in physiological response to atmospheric vapor pressure deficits, indicating that natural ecotypic variation in stomatal responsiveness to air humidity is likely mediated by ABA accumulation in leaf tissue. This research demonstrates that ecotypes of red maple may be selected for atmospheric drought tolerance based-on site moisture conditions.