Why small fluxes matter: the case and approaches for improving measurements of photosynthesis and (photo)respiration.
Since its inception, the Farquhar et al. (1980) model of photosynthesis has been a mainstay for relating biochemistry to environmental conditions from chloroplast to global levels in terrestrial plants. Many variables could be assigned from basic enzyme kinetics, but the model also required measurements of maximum rates of photosynthetic electron transport (J max ), carbon assimilation (Vcmax ), conductance of CO2 into (g s ) and through (g m ) the leaf, and the rate of respiration during the day (R d ). This review focuses on improving the accuracy of these measurements, especially fluxes from photorespiratory CO2, CO2 in the transpiration stream, and through the leaf epidermis and cuticle. These fluxes, though small, affect the accuracy of all methods of estimating mesophyll conductance and several other photosynthetic parameters because they all require knowledge of CO2 concentrations in the intercellular spaces. This review highlights modified methods that may help to reduce some of the uncertainties. The approaches are increasingly important when leaves are stressed or when fluxes are inferred at scales larger than the leaf.
Department of Biology, MSC03-2020, 1 University of New Mexico, Albuquerque, NM 87131, USA dthanson@unm.edu.
David T
0000-0003-0964-9335
DT
Hanson
Department of Biology, MSC03-2020, 1 University of New Mexico, Albuquerque, NM 87131, USA.
Samantha S
SS
Stutz
Interdisciplinary Plant Group, 1-31 Agriculture Building, University of Missouri, Columbia, MO 65211, USA.
John S
JS
Boyer
D002245:Carbon Dioxide / Q000032:analysis / Q000378:metabolism; D002736:Chloroplasts / Q000737:chemistry / Q000378:metabolism; D010788:Photosynthesis / Q000502:physiology*; D018515:Plant Leaves / Q000737:chemistry / Q000502:physiology; D018526:Plant Transpiration / Q000502:physiology
D002245:Carbon Dioxide
Diffusion; internal leaf CO2; mesophyll conductance; photosynthesis; respiration; stomatal conductance; xylem CO2.