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Whole‐tree mesophyll conductance reconciles isotopic and gas‐exchange estimates of water‐use efficiency
Author(s) -
Gimeno Teresa E.,
Campany Courtney E.,
Drake John E.,
Barton Craig V.M.,
Tjoelker Mark G.,
Ubiererea,
Marshall John D.
Publication year - 2021
Publication title -
new phytologist
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 3.742
H-Index - 244
eISSN - 1469-8137
pISSN - 0028-646X
DOI - 10.1111/nph.17088
Subject(s) - photosynthesis , water use efficiency , stomatal conductance , transpiration , carbon dioxide , photosynthetic capacity , δ13c , botany , biology , horticulture , chemistry , ecology , stable isotope ratio , physics , quantum mechanics
Summary Photosynthetic water‐use efficiency (WUE) describes the link between terrestrial carbon (C) and water cycles. Estimates of intrinsic WUE (iWUE) from gas exchange and C isotopic composition (δ 13 C) differ due to an internal conductance in the leaf mesophyll ( g m ) that is variable and seldom computed. We present the first direct estimates of whole‐tree g m , together with iWUE from whole‐tree gas exchange and δ 13 C of the phloem (δ 13 C ph ). We measured gas exchange, online 13 C‐discrimination, and δ 13 C ph monthly throughout spring, summer, and autumn in Eucalyptus tereticornis grown in large whole‐tree chambers. Six trees were grown at ambient temperatures and six at a 3°C warmer air temperature; a late‐summer drought was also imposed. Drought reduced whole‐tree g m . Warming had few direct effects, but amplified drought‐induced reductions in whole‐tree g m . Whole‐tree g m was similar to leaf g m for these same trees. iWUE estimates from δ 13 C ph agreed with iWUE from gas exchange, but only after incorporating g m . δ 13 C ph was also correlated with whole‐tree 13 C‐discrimination, but offset by −2.5 ± 0.7‰, presumably due to post‐photosynthetic fractionations. We conclude that δ 13 C ph is a good proxy for whole‐tree iWUE, with the caveats that post‐photosynthetic fractionations and intrinsic variability of g m should be incorporated to provide reliable estimates of this trait in response to abiotic stress.