To understand leaf photosynthesis characteristics and its response to K starvation in oilseed rape,a field experiment was carried out on K- deficient soil with K deficiency(- K) and K supply( + K) treatments.Gas exchange,chlorophyll fluorescence and chloroplast ultrastructure were studied using winter oilseed rape cultivar Zheyou 601 during over- wintering period. Results showed that leaf net photosynthetic rate( Pn) decreased by45. 1% under- K condition. Although stomatal conductance( gs) was lower in- K t...