Response of photosynthetic characteristics to Mn nutrition in soybean seedling

With two soybean(Glycine max) varieties,Dongbei 85411(DB854-11) and Zhechun No.2(ZC2) as experimental materials,the responses of photosynthetic characteristics in soybean leaves to different manganese(Mn) concentration(0,0.05,0.5,5,30,50 mg/L) were studied.The results showed that minimal fluorescence(Fo),maximum fluorescence(Fv),maximal photochemical efficiency of PSⅡ(Fv/Fm),the potential activities of PSⅡ(Fv/Fo),photochemical quenching(qP) were enhanced with low concentration of Mn,but the Fo,Fm, Fv/Fm,Fv/Fo,qP were reduced with high concentration of Mn.With the increasing of Mn concentration,non-photochemical quenching coefficient(qN) was increased.Appropriate concentration of Mn significantly increased photosynthetic rate(Pn),transpiration rate(Tr),stomatal conductance(Gs) and decreased stomata resistance(Rs) and intercellular CO2 concentration(Ci).With the increasing of Mn concentration,Pn,Tr and Gs in soybean leaves were reduced,while Rs,Ci increased.Fo reached the maximum value at the concentration of 0.5 mg/L Mn2+,but Fm,qP,Fv/Fm,Fv/Fo was maximum at 5 mg/L Mn2+,which indicated that for the photosynthesis was promoted when the concentration of Mn2+ between 0.5 mg/L and 5 mg/L.Under 50 mg/L Mn2+treatment,qN,Rs,Ci reached the maximum and Tr,Pn reduced to the minimum. The negative effect on soybean growth was resulted from the dissipation of excess light energy and reduction of photosynthetic rate.There was a genotypic difference between the two varieties of soybean.Zhechun No.2 was more Mn-tolerant than Dongbei 854-11 soybean.