title: Loss of photosynthetic efficiency in the shade. An Achilles heel for the dense modern stands of our most productive C4 crops?
abstract: The wild progenitors of major C4crops grew as individuals subjected to little shading. Today they are grown in dense stands where most leaves are shaded. Do they maintain photosynthetic efficiency in these low light conditions produced by modern cultivation? The apparent maximum quantum yield of CO2assimilation (ΦCO2max,app), a key determinant of light-limited photosynthesis, has not been systematically studied in field stands of C4crops. ΦCO2max,app was derived from the initial slope of the response of leaf CO2uptake (A) to photon flux (Q). Leaf fractional light absorptance (α) was measured to determine the absolute maximum quantum yield of CO2assimilation on an absorbed light basis (ΦCO2max,abs). Light response curves were determined on sun and shade leaves of 49 field plants of Miscanthus × giganteus and Zea mays following canopy closure. ΦCO2max,app and ΦCO2max,abs declined significantly by 15-27% (P<0.05) with canopy depth. Experimentally, leaf age was shown unlikely to cause this loss. Modeling canopy CO2assimilation over diurnal courses suggested that the observed decline in ΦCO2max,app with canopy depth costs 10% of potential carbon gain. Overcoming this limitation could substantially increase the productivity of major C4crops.
authors.affiliation: University of Illinois, Carl Woese Institute for Genomic Biology and Departments of Crop Sciences and of Plant Biology, 1206 W Gregory Drive, Urbana, IL 61801, USA.
authors.forename: Charles P
authors.initials: CP
authors.lastname: Pignon
authors.affiliation: University of Illinois, Carl Woese Institute for Genomic Biology and Departments of Crop Sciences and of Plant Biology, 1206 W Gregory Drive, Urbana, IL 61801, USA.
authors.forename: Deepak
authors.initials: D
authors.lastname: Jaiswal
authors.affiliation: University of Illinois, Carl Woese Institute for Genomic Biology and Departments of Crop Sciences and of Plant Biology, 1206 W Gregory Drive, Urbana, IL 61801, USA.
authors.forename: Justin M
authors.initials: JM
authors.lastname: McGrath
authors.affiliation: University of Illinois, Carl Woese Institute for Genomic Biology and Departments of Crop Sciences and of Plant Biology, 1206 W Gregory Drive, Urbana, IL 61801, USA slong@illinois.edu.|Lancaster Environment Centre, Lancaster University, Lancaster LA1 4YQ, UK.
authors.forename: Stephen P
authors.identifier: 0000-0002-8501-7164
authors.initials: SP
authors.lastname: Long
mesh_terms: D003624:Darkness; D008954:Models, Biological; D010788:Photosynthesis; D003313:Zea mays / Q000378:metabolism*
keywords: C4 photosynthesis; canopy photosynthesis; corn; crop photosynthesis; crop yield; food security; maize; miscanthus; planting density.; quantum yield; shade acclimation