Effect of glyphosate on photosynthesis and chlorophyll fluorescence of leaves of glyphosate-resistant soybean Glycine max (L.) Merr. seedlings under phosphorus deficiency stress

Effect of glyphosate on photosynthesis and chlorophyll fluorescence parameters of leaves of glyphosate-resistant soybean seedlings (RR1) under phosphorus deficiency stress was studied using a solution culture experiment under phosphorus deficiency stress at the true leaf stage. The glyphosate at 4.98 mL/L was sprayed at the two-trifoliolate leaf stage, and physiological indexes were analyzed 5 days after the glyphosate spraying. The results show that under the phosphorus deficiency stress, the photosynthetic rate (Pn), stomatal conductance (Gs), intercellular CO2 concentration (Ci), maximum fluorescence (Fm), PSII maximum quantum yield (Fv/Fm), PSII effective quantum yield［Y(Ⅱ)］, PS II energy dissipation in non-regulatory quantum yield［Y(NO)］, half saturation light intensity (IK) and maximum electron transport rate (ETRmax) in leaves of RR1 treated by 4.98 mL/L glyphosate are lower than those treated by water under normal phosphorus condition, while the stomatal limitation value (Ls), chlorophyll a (Chl a), chlorophyll b (Chl b), chlorophyll a/b (Chl a/b), carotenoid (Car), total chlorophyll (Chl) content and regulation of PSⅡ quantum yield of energy dissipation［Y(NPQ)］ treated by glyphosate under phosphorus deficiency stress are higher than those treated by water under normal phosphorus conditions. It suggests that spraying herbicide glyphosate under phosphorus deficiency stress decreases photosynthetic rate in leaves of Roundup Ready Soybean significantly. The stomatal limitation resulted from phosphorus deficiency stress may be the main reason for the decline of photosynthetic rate, and the decreased photosynthetic rate leads to reduce the openness of PSⅡ reaction center, PSⅡ activity, electrons in CO2 fixation and photochemical efficiency.