Journal Article

Transpiration efficiency of a tropical pioneer tree (<i>Ficus insipida</i>) in relation to soil fertility

Lucas A. Cernusak, Klaus Winter, Jorge Aranda, Benjamin L. Turner and John D. Marshall

in Journal of Experimental Botany

Published on behalf of Society for Experimental Biology

Volume 58, issue 13, pages 3549-3566
Published in print October 2007 | ISSN: 0022-0957
Published online October 2007 | e-ISSN: 1460-2431 | DOI:

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The response of whole-plant water-use efficiency, termed transpiration efficiency (TE), to variation in soil fertility was assessed in a tropical pioneer tree, Ficus insipida Willd. Measurements of stable isotope ratios (δ13C, δ18O, δ15N), elemental concentrations (C, N, P), plant growth, instantaneous leaf gas exchange, and whole-plant water use were used to analyse the mechanisms controlling TE. Plants were grown individually in 19 l pots with non-limiting soil moisture. Soil fertility was altered by mixing soil with varying proportions of rice husks, and applying a slow release fertilizer. A large variation was observed in leaf photosynthetic rate, mean relative growth rate (RGR), and TE in response to experimental treatments; these traits were well correlated with variation in leaf N concentration. Variation in TE showed a strong dependence on the ratio of intercellular to ambient CO2 mole fractions (ci/ca); both for instantaneous measurements of ci/ca (R2=0.69, P <0.0001, n=30), and integrated estimates based on C isotope discrimination (R2=0.88, P <0.0001, n=30). On the other hand, variations in the leaf-to-air humidity gradient, unproductive water loss, and respiratory C use probably played only minor roles in modulating TE in the face of variable soil fertility. The pronounced variation in TE resulted from a combination of the strong response of ci/ca to leaf N, and inherently high values of ci/ca for this tropical tree species; these two factors conspired to cause a 4-fold variation among treatments in (1–ci/ca), the term that actually modifies TE. Results suggest that variation in plant N status could have important implications for the coupling between C and water exchange in tropical forest trees.

Keywords: Carbon isotope; oxygen isotope; soil fertility; transpiration efficiency; tropical tree

Journal Article.  11240 words.  Illustrated.

Subjects: Plant Sciences and Forestry

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