Deciduous Hardwood Photosynthesis: Species Differences, Temporal Patterns, and Responses to Soil-Water Deficits

Abstract

Changes in regional precipitation patterns will directly impact soil and foliage water status, resulting in physiological modifications in trees that can affect carbon assimilation rates (Briggs et al. 1986; Teskey et al. 1986; Ni and Pallardy 1992). Decreasing water potentials in the root and/or foliage can affect the carbon assimilation by adjusting stomatal conductance (Hinckley et al. 1978a; Epron and Dreyer 1993; Lowenstein and Pallardy 1998) or possibly by directly impacting the biochemical potential for carbon assimilation in the leaf (Lawlor 1995; Escalona et al. 1999). Tree species differ in their morphology and use of physiologic adaptations to avoid the negative impacts of drought on carbon assimilation (Hinckley et al. 1978b; Bahari et al. 1985; Briggs et al. 1986; Ni and Pallardy 1992; Abrams and Mostoller 1995; Lowenstein and Pallardy 1998; Tschaplinski et al. 1998). Species-specific differences in gas-exchange response to drought depend on characteristics such as rooting depth, stomatal sensitivity, osmotic adjustment, cavitation avoidance, and increased tolerance of desiccation (Abrams 1990; Lowenstein and Pallardy 1998; Tshaplinski et al. 1998). For example, because of their deep rooting habit, Quercus species are expected to outcompete the more mesic Acer and Cornus species in dry climates (Hinckley et al. 1979; Bahari et al. 1985; Abrams 1990). Species also may differ in their ability to recover predrought photosynthetic rates following a precipitation event (Ni and Pallardy 1992). Because of shallower rooting depths and limited water-storage capacity, photosynthesis of understory species and saplings is expected to be more sensitive to drying when compared to large overstory trees (Donovan and Ehleringer 1991; Flanagan et al. 1992).