Gas exchange and chlorophyll fluorescence research on different position leaves of rice plant.

Responses of gas exchange and chlorophyll fluorescence parameters to photosynthetic photon densities(PFD),and alternations in contents of photosynthetic pigments,nitrogen and phosphorus were investigated in different position leaves at the heading day in rice plants.The results showed that net photosynthetic rate(Pn),stomatal conductance(Gs),transpiration rate(E) decreased significantly with lowering of leaf positions.In lower two leaves,intercellular CO2 concentration(Ci) declined greatly at lower PFD(800 μmol·m-2·s-1),while they increased at higher PFD,which were even much higher than that in higher two.These results showed that the decline of Pn didn't mainly result from stomatal factors.The increase of initial fluorescence(Fo) and the reduction of photosystem Ⅱ(PSⅡ) maximum photochemical quantum yield(Fv/Fm) indicated PSⅡ reaction center suffered inactivation or/and damage.Furthermore,PSⅡefficient photochemical quantum yield(Fv′/Fm′),PSⅡ actual photochemical quantum yield(ΦPSⅡ),photochemical quenching(qP) and apparent electron transport rate(ETR) were also declined,suggesting not only the absorption but also the transformation and transfer of light energy were seriously inhibited.These caused the decomposition of chlorophyll(Chl) and the reduction of nitrogen(N) and phosphorus(P) contents,although non-photochemical quenching(NPQ) and the contents of carotenoid(Car) continued to increase in response to the inhibition in high energy utilization with lowering of leaf positions.