Leaf abscisic acid accumulation in response to substrate water content: Linking leaf gas exchange regulation with leaf abscisic acid concentration

Quantitative differences in leaf abscisic acid (ABA(L)) among four cultivars of red maple (Acer rubrum L.) and one freeman maple (Acer xfreemanii E. Murray) cultivar were investigated. This study tested the hypothesis that ABA(L) concentration can be used to compare the effects of water stress on the gas exchange response of five different maple genotypes, including four red maple cultivars ['Summer Red', 'October Glory', 'Autumn Flame', and 'Franksred'('Red Sunset')] and one hybridized freeman maple cultivar ['Jeffersred'('Autunm Blaze')]. Two-year-old cloned genotypes of red maple and freeman maple were subjected to two treatments: irrigated daily to container capacity or irrigation withheld for one drought and recovery cycle. Leaf abscisic acid concentration, gas exchange, and whole-tree sap flow measurements were conducted under well-watered and drought stress conditions. Over the course of the drought stress and recovery phase, net photosynthesis (A(net)), stomatal conductance (g(s)), and transpiration (E) declined as ABA(L) and instantaneous water use efficiency (A/g(s)) increased. Until severe water stress conditions were prominent, water use was higher in 'Summer Red' as compared to 'October Glory'. This study found that ABA(L) tracked g(s) and that stomatal responsiveness to substrate moisture deficit is likely mediated by ABA accumulation in leaf tissue. This research demonstrates a leaf level physiological response to substrate volumetric water content that appears to depend on ABA(L) concentration. In addition, the evidence in this study indicates that ABA(L) may be used as a potential surrogate for the g(s) response to substrate water stress and could become part of a cultivar drought tolerance selection strategy for red maple and freeman maple.