Journal
NEW PHYTOLOGIST
Volume 206, Issue 2, Pages 637-646Publisher
WILEY-BLACKWELL
DOI: 10.1111/nph.13296
Keywords
Craig-Gordon model; leaf water enrichment; oxygen isotope; Peclet effect; transpiration
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Funding
- Australian Research Council [FT0992063]
- Australian Research Council [FT0992063] Funding Source: Australian Research Council
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The two-pool and Peclet effect models represent two theories describing mechanistic controls underlying leaf water oxygen isotope composition at the whole-leaf level (O-18(L)). To test these models, we used a laser spectrometer coupled to a gas-exchange cuvette to make online measurements of O-18 of transpiration (O-18(trans)) and transpiration rate (E) in 61 cotton (Gossypium hirsutum) leaves. O-18(trans) measurements permitted direct calculation of O-18 at the sites of evaporation (O-18(e)) which, combined with values of O-18(L) from the same leaves, allowed unbiased estimation of the proportional deviation of enrichment of O-18(L) from that of O-18(e) (f) under both steady-state (SS) and non-steady-state (NSS) conditions. Among all leaves measured, f expressed relative to both O-18 of transpired water (f(trans)) and source water (f(sw)) remained relatively constant with a mean SD of 0.11 +/- 0.05 and 0.13 +/- 0.05, respectively, regardless of variation in E spanning 0.8-9.1mmolm(-2)s(-1). Neither f(trans) nor f(sw) exhibited a significant difference between the SS and NSS leaves at the P<0.05 level. Our results suggest that the simpler two-pool model is adequate for predicting cotton leaf water enrichment at the whole-leaf level. We discuss the implications of adopting a two-pool concept for isotopic applications in ecological studies.
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