Conifers, Angiosperm Trees, and Lianas: Growth, Whole-Plant Water and Nitrogen Use Efficiency, and Stable Isotope Composition (δ  13C and δ  18O) of Seedlings Grown in a Tropical Environment  

Abstract

Seedlings of several species of gymnosperm trees, angiosperm trees, and angiosperm lianas were grown under tropical field conditions in the Republic of Panama; physiological processes controlling plant C and water fluxes were assessed across this functionally diverse range of species. Relative growth rate, r, was primarily controlled by the ratio of leaf area to plant mass, of which specific leaf area was a key component. Instantaneous photosynthesis, when expressed on a leaf-mass basis, explained 69% of variation in r (P , 0.0001, n 5 94). Mean r of angiosperms was significantly higher than that of the gymnosperms; within angiosperms, mean r of lianas was higher than that of trees. Whole-plant nitrogen use efficiency was also significantly higher in angiosperm than in gymnosperm species, and was primarily controlled by the rate of photosynthesis for a given amount of leaf nitrogen. Whole-plant water use efficiency, TE c , varied significantly among species, and was primarily controlled by c i /c a , the ratio of intercellular to ambient CO 2 partial pressures during photosynthesis. Instantaneous measurements of c i /c a explained 51% of variation in TE c (P , 0.0001, n 5 94). Whole-plant 13 C discrimination also varied significantly as a function of c i /c a (R 2 5 0.57, P , 0.0001, n 5 94), and was, accordingly, a good predictor of TE c . The 18O enrichment of stem dry matter was primarily controlled by the predicted 18 O enrichment of evaporative sites within leaves (R 2 5 0.61, P , 0.0001, n 5 94), with some residual variation explained by mean transpiration rate. Measurements of carbon and oxygen stable isotope ratios could provide a useful means of parameterizing physiological models of tropical forest trees.Tropical forest ecosystems have been subject to extensive perturbations associated with anthropogenic activity in recent decades, and such perturbations will likely continue into the foreseeable future (Laurance et al., 2004;Wright, 2005). Effective environmental management requires knowledge of how such perturbations impact upon cycling of carbon (C) and water between forest trees and the atmosphere, and how these C and water fluxes relate to plant nutrient status. A sound, mechanistic understanding of the physiological processes that control photosynthesis and transpiration in tropical trees is therefore essential for understanding and managing the human impact upon tropical forests. In this study, we analyzed the physiological controls over growth (the relative rate of C accumulation), nitrogen (N) use efficiency (NUE; the rate of C accumulation for a given N content), water use efficiency (the ratio of whole-plant C gain to water loss), and stable isotope composition (d 13

Responses of Legume Versus Nonlegume Tropical Tree Seedlings to Elevated CO2 Concentration

“…7, C and D; Table I). This agrees with previous observations for a smaller number of species (Cernusak et al, 2007a(Cernusak et al, , 2008(Cernusak et al, , 2009b. When plants were grown in fertilized soil, the legume species appeared to lose their advantage in W P , as shown for the comparison between O. macrocalyx and S. macrophylla in this study (Fig.…”

Two tropical conifers show strong growth and water-use efficiency responses to altered CO2concentration

“…Both Tabebuia and Chrysophyllum have been used extensively in previous ecophysiological work in Panama (e.g. Cernusak et al, 2008Cernusak et al, , 2011. All four genera form arbuscular mycorrhizal associations (Dickie and Holdaway, 2010).…”

Photosynthetic physiology of eucalypts along a sub-continental rainfall gradient in northern Australia

“…. The d was previously estimated to have a mean value of about 3‰ in 15 tropical tree species (Cernusak et al, 2008), with other estimates in the literature ranging from about 0 to 4‰ (Cernusak et al, 2007;Hubick, 1990;Hubick and Farquhar, 1989;Hubick et al, 1986). The c i /c a is controlled by the balance between photosynthesis (A) and stomatal conductance (g s ).…”