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Intrinsic Water-Use Efficiency and Heterotrophic Investment in Tropical Leaf Growth of Two Neotropical Pioneer Tree Species as Estimated from δ 13 C Values

V. J. Terwilliger, K. Kitajima, D. J. Le Roux-Swarthout, S. Mulkey and S. J. Wright
The New Phytologist
Vol. 152, No. 2 (Nov., 2001), pp. 267-281
Published by: Wiley on behalf of the New Phytologist Trust
Stable URL: http://www.jstor.org/stable/1353766
Page Count: 15
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Since scans are not currently available to screen readers, please contact JSTOR User Support for access. We'll provide a PDF copy for your screen reader.
Intrinsic Water-Use Efficiency and Heterotrophic Investment in Tropical Leaf Growth of Two Neotropical Pioneer Tree Species as Estimated from δ 13 C Values
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Abstract

13 C enrichment in emerging leaves and its effect on carbon isotopic composition (δ 13 C) of mature leaves were investigated in the neotropical pioneer tree species, Cecropia longipes and Urera caracasana, in Panama. • Leaves of all ages were analysed for δ 13 C, gas exchange, nitrogen, and leaf mass per area. Low intercellular to atmospheric carbon dioxide ( CO2) partial pressure ( p i: p a); and high δ 13 C of CO2 in air, intrinsic water-use efficiency, internal resistance, and carboxylation capacity were discounted as causes of 13 C enrichment. • 13 C enrichment might occur when leaf growth is from imported organic carbon but might not reflect δ 13 C values at the leaf producing the carbon. Results support hypotheses that: de novo sucrose synthesis causes 13 C enrichment of mobile sugars after export from source leaves; and high ratios of PEP carboxylase (PEPc): PEPc + Rubisco cause emerging leaves to be 13 C enriched relative to their growth substrate. Carbon contributions of 13 C-enriched early growth could yield inaccurate p i: p a estimates from δ 13 C in mature leaves. • A model estimated investment of imported organic carbon to leaf growth and improved estimates of p i: p a from mature leaves. With such adjustment, δ 13 C analyses provide valuable information about age-related source-sink relations in leaves.

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