Is photosynthetic acclimation to free-air CO2 enrichment (FACE) related to a strong competition for the assimilatory power between carbon assimilation and nitrogen assimilation in rice leaf?
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Net photosynthetic rate (PN) of leaves grown under free-air CO2 enriched condition (FACE, about 200 µmol mol−1 above ambient air) was significantly lower than PN of leaves grown at ambient CO2 concentration (AC) when measured at CO2 concentration of 580 µmol mol−1. This difference was found in rice plants grown at normal nitrogen supply (25 g m−2; NN-plants) but not in plants grown at low nitrogen supply (15 g m−2; LN-plants). Namely, photosynthetic acclimation to FACE was observed in NN-plants but not in LN-plants. Different from the above results measured in a period of continuous sunny days, such photosynthetic acclimation occurred in NN-plants, however, it was also observed in LN-plants when PN was measured before noon of the first sunny day after rain. Hence strong competition for the assimilatory power between nitrogen (N) and carbon (C) assimilations induced by an excessive N supply may lead to the photosynthetic acclimation to FACE in NN-plants. The hypothesis is supported by the following facts: FACE induced significant decrease in both apparent photosynthetic quantum yield (Φc) and ribulose-1,5-bisphosphate (RuBP) content in NN-plants but not in LN-plants.
Additional key wordsapparent quantum yield carboxylation efficiency net photosynthetic rate nitrogen supply Oryza ribulose-1,5-bisphosphate regeneration
ambient CO2 concentration
intercellular CO2 concentration
free-air CO2 enrichment
maximum in vivo electron transport rate
net photosynthetic rate
photosynthetic photon flux density
maximum in vivo carboxylation rate
apparent quantum yield of carbon assimilation
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