Intraspecific variation in hydraulic conductance and water use efficiency of oak trees and seedlings across natural and experimental hydrologic gradients.
Cavender-Bares, Jeannine*,1, 3, Miles, Brianna1, 3, Terwilliger, Valery2, 3, Urgenson, Lauren3, 5, Parker, Geoffrey3, Lovelock, Catherine3, 4, 1 Ecology, Evolution & Behavior, St. Paul, MN, USA3 Smithsonian Environmental Research Center, Edgewater, MD, USA2 Geography Department, Lawrence, KS, USA5 University of Washington, Seattle, WA, USA4 Center for Marine Studies, Brisbane, Queensland, AU
ABSTRACT- We examined water transport in seedlings and mature trees in the genus Quercus across natural and experimental hydrologic gradients. The goals of the study were 1) to compare the sapflow, whole plant hydraulic conductance and water use efficiency (WUE) of three oak species with contrasting microenvironments in an extremely dry and an extremely wet year; 2) to compare whole plant hydraulic conductance, water use efficiency and other physiological parameters of seedlings (seven species) grown across an experimental hydrologic gradient, and 3) to determine whether the degree of plasticity of each species in their functional traits is related to their habitat breadth across an elevation gradient. We found that among mature trees, Quercus palustris, a predominantly floodplain species, shows higher sapflow in wet environments than Q. alba and Q. falcata, two upland oak species. In upland sites, Q. alba and Q. falcata show maximal sapflow rates, and both species show higher sapflow in an extreme drought year than under conditions of flooding. Seedlings of Quercus palustris also showed higher whole plant hydraulic conductance in saturated soils than more upland species. At the same time, upland species showed a greater capacity to increase WUE under drought conditions than lowland species, as determined by instantaneous measurements and stable carbon isotope ratios. For all species, we found that non-photochemical quenching increased in drought stressed plants, which is likely to be a protective mechanism against excess light energy when photosynthetic capacity is reduced. Our results indicate that physiological function under optimal conditions is similar among closely related sympatric species, but species responses to extreme conditions is highly predictive of their actual distributions.
Key words: sapflow, Quercus, hydrologic gradient, whole plant hydraulic conductance
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