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Variations in structural,biochemical, and physiological traits of photosynthesis and resource use efficiency in Amaranthus species (NAD-ME-type C4)
Authors:Nobuko Tsutsumi  Miyuki Tohya  Taiken Nakashima
Institution:1. Graduate School of Bioresource and Bioenvironmental Sciences, Kyushu University, Fukuoka, Japan;2. School of Agriculture, Kyushu University, Fukuoka, Japan
Abstract:C4 plants show higher photosynthetic capacity and productivity than C3 plants owing to a CO2-concentrating mechanism in leaves, which reduces photorespiration. However, which traits regulate the photosynthetic capacity of C4 plants remains unclear. We investigated structural, biochemical, and physiological traits associated with photosynthesis and resource use efficiency in 20 accessions of 12 species of Amaranthus, NAD-malic enzyme-type C4 dicots. Net photosynthetic rate (PN) ranged from 19.7 to 40.5 μmol m?2 s?1. PN was positively correlated with stomatal conductance and nitrogen and chlorophyll contents of leaves and was weakly positively correlated with specific leaf weight. PN was also positively correlated with the activity of the C3 enzyme ribulose-1,5-bisphoshate carboxylase/oxygenase, but not with the activities of the C4 enzymes phosphoenolpyruvate carboxylase and NAD-malic enzyme. Structural traits of leaves (stomatal density, guard cell length, leaf thickness, interveinal distance, sizes of mesophyll and bundle sheath cells and the area ratio between these cells) were not significantly correlated with PN. These data suggest that some of the biochemical and physiological traits are involved in interspecific PN variation, whereas structural traits are not directly involved. Photosynthetic nitrogen use efficiency ranged between 260 and 458 μmol mol?1 N s?1. Photosynthetic water use efficiency ranged between 5.6 and 10.4 mmol mol?1. When these data were compared with previously published data of C4 grasses, it is suggested that common mechanisms may determine the variations in resource use efficiency in grasses and this dicot group.
Keywords:Amaranthus  C4 photosynthesis  leaf anatomy  NAD-malic enzyme type  photosynthetic nitrogen use efficiency  photosynthetic rate  photosynthetic water use efficiency
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