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New insights into the covariation of stomatal, mesophyll and hydraulic conductances from optimization models incorporating nonstomatal limitations to photosynthesis
Author(s) -
Dewar Roderick,
Mauranen Aleksanteri,
Mäkelä Annikki,
Hölttä Teemu,
Medlyn Belinda,
Vesala Timo
Publication year - 2018
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.14848
Subject(s) - stomatal conductance , photosynthesis , conductance , vapour pressure deficit , chemistry , botany , c4 photosynthesis , water use efficiency , horticulture , transpiration , biophysics , mathematics , biology , combinatorics
Summary Optimization models of stomatal conductance ( g s ) attempt to explain observed stomatal behaviour in terms of cost‐‐benefit tradeoffs. While the benefit of stomatal opening through increased CO 2 uptake is clear, currently the nature of the associated cost(s) remains unclear. We explored the hypothesis that g s maximizes leaf photosynthesis, where the cost of stomatal opening arises from nonstomatal reductions in photosynthesis induced by leaf water stress. We analytically solved two cases, CAP and MES, in which reduced leaf water potential leads to reductions in carboxylation cap acity ( CAP ) and mes ophyll conductance ( g m ) (MES). Both CAP and MES predict the same one‐parameter relationship between the intercellular : atmospheric CO 2 concentration ratio ( c i / c a ) and vapour pressure deficit (VPD, D ), viz. c i / c a ≈ ξ /( ξ + √ D ), as that obtained from previous optimization models, with the novel feature that the parameter ξ is determined unambiguously as a function of a small number of photosynthetic and hydraulic variables. These include soil‐to‐leaf hydraulic conductance, implying a stomatal closure response to drought. MES also predicts that g s / g m is closely related to c i / c a and is similarly conservative. These results are consistent with observations, give rise to new testable predictions, and offer new insights into the covariation of stomatal, mesophyll and hydraulic conductances.