Study On Photosythetic Characteristics And Osmotic Adjedgement Of Desert Plants Cynanchum Komarovii

Cynanchum komarovii is the main constructive plants in Maowusu desert. The photosynthesis characteristics of Cynanchum komarovii was dynamic studied under natural conditions. The result indicated that the diurnal changes of net photosynthetic rate (Pn) of Cynanchum komarovii displayed significantly less symmetrical two-peak pattern, with a predominant peak in ll:00am and a small peak in 16:00pm. On hot bright sunny day. But the diurnal changes of transpiration (Tr) and stomatal conductance (Cs) of Cynanchum komarovii shown very different with that of Pn , they exhibited no peak all the day. The photosynthesis of different leaves on the same stem is very different, the third expanded leaf is the highest among them. The analysis of diurnal changes of chlorophyll fluorescence parameters shown that The PSII primarily photo-chemical efficiency (Fv/Fm) and PSII linear electron transport (Yield) were low in the noon, high in the morning and afternoon.The Cynanchum Komarovii seedlings were treated with PEG(6000) in different concentration and treated time in order to inquire into physiological. Response and adaptive regulation mechanism to dried resistance. The result showed that physiological response were mainly affected by concentration of PEG and less affected by time of PEG(6000) treatment. Relative water content of leaves root activity, and growth of roots and plants showed a less reduction under 10-20% PEG(6000) treatment, but ratios of root cap, and contains of soluble sugar, contain of Pro and potassium showed a less increase. All those just described indexes showed a marked change under 25% PEG treatment. Relative water content of leaves, and root activity displayed a apparent reduction. The time of highest contains of soluble sugar appeared was moved up three days . The contains of soluble sugar were less than that of under 20% PEG (6000) treatment. After the period of treatments were prolonged for three days, the contain of sugar reduced again. The growth of roots and plants were retarded severely and the ratios of root cap were increased manifestly. The ratios of root-shoot was stability and the growth almost stopped at the later period of PEG (6000) treatment. Although Cynanchum komarovii has a strong ability to resist to drought, the osmotic regulationcapacity of Cynanchum komarovii was lost under severe water stress of 25% PEG treatment that indicated that 25% PEG concentration was the threshold value of Cynanchum komarovii under the drought stress.The growth and osmolyte accumulation of Cynanchumkomarovii was studied under water stress. Treatments were carried out in PVC tube to simulate drought. The results indicated that Cynanchumkomarovii is sensitive to soil water from root to shoot, which apparently become slower and even stopped growing with water stress aggravation and the time of stress increase, but the root-shoot ratio increased. The soluble sugar is primary osmolyte in roots of cynanchum komarovii, which increased markedly with water stress aggravation, while soluble sugar in leaves decrease. The results showed that assimilation of Cynanchum komarovii mostly distributed to root. The proline in roots, stems and leaves is also important osmolyte. They will accumulate markedly with water stress aggravation. But inorganic ion acted less in osmotic adjustment process of Cynanchum komarovii.