Ecophysiological Responses in Mesic versus Xeric Hardwood Species to an Early-Season Drought in Central Pennsylvania
Field and laboratory studies were used to evaluate net photosynthesis and plant and tissue water relations in saplings of co-occurring xeric (Quercus prinus and Q. ilicifolia) versus mesic (Q. rubra and Castanea dentata) hardwood species during a droughty summer. Mean daily net photosynthesis, leaf conductance, leaf water potential, and water use efficiency were reduced in all four species during the peak drought period. Throughout the study, net photosynthesis and leaf conductance were on average high in Q. ilicifolia and Q. prinus, intermediate in Q. rubra, and low in C. dentata. Leaf water potential was generally highest in C. dentata and not significantly different among the Quercus species. There were few consistent patterns in the tissue water relations data, including a lack of osmotic adjustment during peak drought, a lack of correlation between osmotic potentials and gas exchange rates, decreases in osmotic potentials and tissue elasticity after the peak drought period ended, and bulk leaf water potential values below the osmotic potential at zero turgor, despite relatively high gas exchange in those plants. Thus, the tissue water relations data provided little insight to mechanisms of drought tolerance in these species and suggest some methodology problems using standard pressure-volume procedures. For. Sci. 36(4):970-981.
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