Accumulation and Distribution of Cobalt in Rape and the Effects of Cobalt on the Photosynthesis of Rape Leaves

Soil pot experiment was used to investigate the accumulation and distribution of cobalt in rape(Brassica napus L.)and the effects of cobalt on the photosynthesis of rape leaves.Rape seedlings at the six-leaf stage were treated with different concentration cobalt(0,10,25,50,100mg.kg-1),and the cobalt content in roots,stems and leaves,pigment content,photosynthetic gas exchange parameters and chlorophyll fluorescence characteristics of leaf were investigated on the 7th day after the cobalt treatment.The results showed that:(1)The roots,stems,leaves of rape could absorb and accumulate a certain amount of cobalt,and rape cobalt content and soil cobalt content was a significant positive correlation;there were significant differences in cobalt distribution between the different organs,and the distribution law of cobalt content in rape was:rootsstemsleaves,and old leavesyoung leaves.(2)When the soil cobalt content is 10 mg.kg-1,compared with the control,both of the pigment content of leaf,net photosynthetic rate(Pn),stomatal conductance(Gs),intercellular CO2concentration(Ci),transpiration rate(Tr)significantly increased,after that with the increase of cobalt concentration all of the parameters were significantly decreased,it showed that low concentrations of cobalt could promote the photosynthesis of rape and high concentrations of cobalt significantly inhibit the photosynthesis of rape.(3)Chlorophyll fluorescence analysis showed that the cobalt significantly affected the structure and function of photosystem Ⅱ(PSⅡ)in rape leaves,and high concentrations of cobalt significantly inhibited the activity of the PSⅡreaction center.