The Ionic Response And Physiological Ecological Changes Of Ph. Praecox Under Salt Stress

Soil salinization,threating the development of agriculture, is a global problem. One third of the irrigated land worldwide undergoes salt stress and the soil salinity area increases year by year,which causes heavy losses to agricultural production. Therefore,to select and cultivate salt-tolerant plants species,improve salt tolerance and soil physiochemical properties by chemical modification and biological methods,becomes a major issue fpr agricultural development and needs to be urgently resolved.Phyllostachys praecox cv. prevernalis(Ph. praecox)is an endemic bamboo species for shoot in China. The major cultivation region focuses in Zhejiang province and extends to other provinces owing to the short payback period,good benefits and strong adaptability. It is even widely cultivated in the coastal land of Shangyu,Cixi,Sanmen and Yueqing County in Zhejiang province. However,the salt content in the soil of coastal land is too high to make them grow regularly and some of them have tended to decline or even death. Therefore, the physiological ecological changes under salt stress and mechanism of salt resistance of Ph. praecox were studied in order to resolve this challenge.Ion response and physiological ecological changes of Ph. praecox under salt stress were systematically studied combined with the achievements before. The ionic selective absorption and transportation,accumulation,root activity,membrane permeability,osmotic adjustment and the photosynthesis of Ph. praecox under salt stress conditions are determined.The results showed as follows:(1)The ionic selective absorption capacity increaseed with salt stress concentration,peaked at 0.3% NaCl,and then declined. 6days after treatment,the ionic selective absorption was strong and then declined rapidly with the extension of the treated time. Moreover, appropriate calcium fertilizer could alleviate the damage of salt stress.(2)The ionic selective transportation of ST(root/rhizome)increaseed with salt in soil,and top at 0.3% NaCl treatment,then declined. That of ST(rhizome/branches)was very weak except 0.5% NaCl treatment. With the treatment days of salt stress,the change trend of ST(root/rhizome)and ST(rhizome/branches)was similar,that was,low- high-low-high. High ST was found at early time under the 0.3% NaCl treatment. Besides,ST at earlier time under 0.1% and 0.3% treatment was higher than that under 0.5%.(3)Under salt stress,the distribution of Na~+ and K~+ in different parts of the plant was different. The content of K~+ was far more higher than that of Na~+. The changes of Na~+ and K~+ content were just rendering antagonistic effects under 0.1% and 0.5% NaCl treatment. Each Na~+ and K~+ content in bamboo leaves showed obvious change law. K~+ content of treatment reaches the highest level by the 12th day,and then declined gradually. The change law of Na~+ and K~+ content in rhizome and branch was less regular than that in root and leaf. Na~+ content under 0.5% salt stress was the highest in the last sampling analysis.(4)Ph. praecox under different salt stress maintained high superoxide dismutase(SOD)activity,even higher or similar than the control by the later stage of treatment. The peroxidase(POD)activity under 0.5% NaCl treatment in leaf at later stage decreased slightly compared to the control,while higher and similar than the control at the medium stage and later stage under 0.3% treatment. Proline(Pro)content showed the highest level under low concentrations of salt stress,then declined with increase of concentration. Pro content under 0.3% treatment was similiar with the control and as well as malondialdehyde(MDA)content. MDA content under 0.1% treatment at the later properties stage was lower than control. The correlation between physiological and biochemical indexes was not significant under different treatments. Activity of SOD and POD and content of Pro under 0.3% treatment could maintain a high level thus inhibited membrane lipid peroxidation and kept the content of MDA at lower level.(5)Under salt stress,root system activity of the control was the highest,followed by 0.3% and 0.5%. Ph. praecox showed a certain degree of stress ability at the early stage of salt stress with high root system activity. However,the root system had been damaged and its vigor decreased with the increase of salt concentration and days of treatment.(6)The permeability of cell membrane varied with the concentration of salt stress. That of the control showed the minimal,and of 0.1% and 0.3% treatment was similar,and of 0.5% treatment increased significantly. The change of cell membrane permeability at early stage of salt stress treatment was evident,and stable at the later stage.(7)Chlorophyll content slightly increased under 0.1% treatment,and declined with the increase of salt concentration. Besides,chlorophyll content of different treatments showed trend of high-low-high with the days of treatment. However,the increase of chlorophyll content was not significantly increased at later stage of high concentrations treatment while increased obviously under 0.3% treatment.(8)Net photosynthesis rate(Pn),stomatal conductance(Gs)and transpiration rate(Tr)declined with the increase of salt concentration. The change law of intercellular CO2 concentration(Ci)and stomatal limit value(Ls)was not obvious,but in contrary change trend. Analysis demonstrated that the main cause leading to decline of Pn of Ph. praecox was stomatal limit under low concentration of salt stress at early stage,while non-stomatal limit under high concentration at later stage.(9)Pn diural changes of Ph. praecox showed sigl peak curve and reached maximum at 11:00. However,Pn of the control was higher than that of other three salt stress treatments after 11:00. The diurnal change of Pn and Ls of Ph. praecox under three treatments from 7:00 to 15:00 was similar,showing the trend of rising firstly and declined later,while the diurnal change of Ci showed an opposite trend. Diurnal variation of water use efficiency(WUE)was sigle peak curve.