Photosynthesis and Water Relations During Drought in Acer rubrum L. Genotypes from Contrasting Sites in Central Pennsylvania

Abstract

Variation in gas exchange and water relations during drought, and in leaf morphology were studied in 1-year-old greenhouse-grown Acer rubrum L. seedlings originating from four contrasting sites in central Pennsylvania: bog (hydric), valley (mesic), ridge and barrens (xeric). During the middle and later stages of drought, bog plants had lower net photosynthesis and leaf conductance than did the three upland sources. Bog plants also had higher (less negative) shoot water potential at the incipient wilting point. Day-to-day instantaneous measurements of leaf water potential were unobtainable due to foam from the phloem which obscured initial xylem sap exudation. Bog plants had higher pre-drought osmotic potentials than the barrens plants and were the only source to osmotically adjust between preand 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 plants had leaves with relatively high stomatal density and small guard cells, whereas leaves of bog plants had high specific mass and stomatal density and intermediate guard cell length. Most differences observed in this study 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