Photosynthesis, Water Relations, and Drought Adaptation in Six Woody Species of Oak-Hickory Forests in Central Missouri

Abstract

Responses of photosynthesis, leaf conductance, water potential, and tissue water relations to drought were compared during two growing seasons for saplings of six woody species that occupy natural habitats of varying soil moisture regime. Drought substantially restricted leaf conductance in all angiosperm species ( Quercus velutina, Q. alba, Q. rubra, Cornus florida , and Acer saccharum ), but only slightly reduced conductance of Juniperus virginiana . Cornus florida exhibited the most accentuated response to drought because of its inability to avoid low water potential, a situation attributable to the known shallow rooting habit of this species. Differences in drought adaptation among angiosperms were apparent, with Quercus species exhibiting generally lower osmotic potentials at full turgor and turgor loss point, higher moduli of leaf tissue elasticity, and higher rates of photosynthesis under drought compared with A. saccharum and C. florida . These characteristics would confer a competitive growth advantage to the oaks on dry sites. Juniperus virginiana , a species usually found on very xeric sites, exhibited a very different, but no less effective, pattern of drought adaptation. An inherently low capacity for water loss and the ability to sustain stomatal opening at low water potentials appear to promote the success of this species in dry environments. Forest Sci. 31:557-569.