Photosynthesis and water relations during drought in Acer rubrum L. genotypes from contrasting sites in central Pennsylvania

During the middle and later stages of drought, bog (hydric) plants had lower net photosynthesis and leaf conductance than did 3 upland sources. Bog plants also had higher (less negative) shoot water potential at the incipient wilting point. Bog plants had higher pre-drought osmotic potentials than the barrens plants and were the only source to osmotically adjust between pre- and peak drought. During peak drought there were no differences in osmotic potentials, relative water content at zero turgor or tissue elasticity among any of the sources. Barrens (xeric) plants had leaves with relatively high stomatal density and small guard cells; leaves of bog plants had high specific mass and stomatal density and intermediate guard cell length. Most observed differences were between the bog vs upland sources, and not among the latter. The lack of differences among the upland sources may be due to gene flow between sites or the relatively recent invasion of A. rubrum to the sites. -from Authors