Effects of potassium-deficiency on photosynthesis and energy dissipation in different rice cultivars

Our previous study has demonstrated that Erjiufeng(EJF) is one of potassium-sensitivity rice cultivars,and Yuanfengzao(YFZ) is an insensitive one. In this study,the growth,photosynthetic parameters and chlorophyll fluorescence parameters and dark relaxation kinetics of non-photochemical chlorophyll fluorescence quenching of these two rice cultivars were investigated after 41 days' potassium-deficiency treatment.The results showed that the net photosynthetic rate(Pn) of flag leaves was reduced,and the growth was significantly suppressed under the potassium deficient condition in both cultivars;however,the dominant factors induced Pn lower were different in two cultivars.Pn of flag leaves in YFZ was decreased with decreasing stomatal conductance(Gs) and intercellular CO2 concentration(Ci),but chlorophyll fluorescence parameters and the content of chlorophyll content were quite stable,suggesting that the reduction in Pn could be accounted for the stomatal limitation.However,for EJF,Pn was decreased accompanied with Gs and Ci at lower photosynthetic photon flux densities(PFD) 500 mol/(m2s).At higher PFD,Ci was increased with the decrease of Pn and Gs,and it exceeded the control at 1200 mol/(m2s), indicating that Pn suppression was mainly caused by the non-stomatal factors rather than stomatal limitation.Light saturation point(LSP) of EJF dropped to about 500 mol/(m2s) under potassium deficient condition,while LSP of YFZ was stable at 1200 mol/(m2s) in potassium-deficient plants.Under potassium deficient condition,F'v/F'm,ФPSII,qP and ETR were rapidly decreased with the increase of PFD;while L(PFD),E and PP were dramatically increased,NPQ was increased when PFD was less than 1200 mol/(m2s),but it was rapidly decreased to less than its control under higher PFD.Meanwhile,Fm and Fv/Fm were significantly decreased accompanied by the increase in Fo.All these results suggested that photosynthetic apparatus was damaged under potassium deficient condition,and photoinhibition occurred.Based on dark relaxation kinetics of non-photochemical chlorophyll fluorescence quenching,middle component(qNm) was observed to have a larger contribution to energy dissipation,and part of excited energy could be transferred from PSⅡ to PSⅠ,thus the pressure of dissipating energy was reduced.In conclusion,different rice cultivars of potassium sensitivity may also be partially related to their protection capacity against photodamage under prolonged potassium deficient conditions.