Wheat Growth As Affected By Salinity-alkalinity Stress And Regulation Humic Acid

Four kinds of salt including NaCl,Na2SO4,NaHCO3 and Na2CO3 are used to simulate 20 kinds of different salinity-alkalinity conditions. The concentration of Na+, CO32- and pH are identified as typical factors by principal component analysis that the effect of salt-alkali environment to wheat stress in the paper. On this basis, five different concentrations of NaCl and Na2CO3 are selected for stress treatments of water cultivation wheat seedlings after soaking the seed by humic acid, different action mechanism of salinity-alkalinity stress and control effects of humid acid to saline alkali tolerance of wheat are discussed by the research of seed germination, carbon and nitrogen metabolism, photosynthesis, ion steady-state, antioxidation system and rhizosphere environment.The results show that high salt concentration, especially increasing proportion of CO32-decreased water absorption capacity andα-amylase activity, inhibited radicle growth, reduced seed vigor, slowed the germination speed, weakened sprout strength, finally decreased germination rate. After wheat emerge, decreasing total absorption area of root, increasing active absorption area, root vigor and absorption capacity of K+ maintained high K/Na and the activity of phenylalanine aminolyase(PAL) in leaves and relieved enviornment pressure by high concentrations of salinity-alkalinity.Seedling maintained plasma membrane integrity under salinity-alkalinity stress by improved the activity of sucrose phosphate synthase(SPS), increasing the content of sucrose, the accumulation of soluble sugar and decreasing osmotic potential. Defense mechanism of seedling decreased with increasing stress concentration, which the content of soluble sugar, endogenous nitrate reductases activity and the concentration of soluble protein decreased, nitrate nitrogen reduced, the activity of glutamine synthase increased. Especially the harm of alkali stress is stronger than salt stress which has a greater effect on the activity of glutamine synthelase(GS), and produce higher accumulation of ammonium nitrogen than salt stress.The accumulation of malondialdehyde(MDA)in root and seedling increased further under salinity-alkalinity stress, the activity of peroxidase (POD) enhanced, the activity of super oxide dlsmutase(SOD) decreased, however, the proline content increased, the activity of CAT improved, the activity of POD decreased and the activity of SOD first rises then descends in leaves. The activity of antioxidant enzymes under alkali stress are higher than that under salt stress with same concentration. The production of active oxygen and balance of removing system are broken which improved conductivity of root and leaves dramaticlly by increasing salinity-alkalinity stress concentration. Stomatal conductance, transpiration rate and water use efficiency decreased, however, intercellular carbon dioxide concentration increased, Ls and chlorophyll content decreased, net photosynthetic rate decilined under salinity-alkalinity stress of short time. photosynthetic rate of leaves decreased, phosphate concentrations in rhizosphere increased, however, the concentration of Ca2+, Mg2+ and concentration variation of Cl- decreased, inhibited the NSCCs activity, decreased absorption rate of Na+, improved K+/Na+. The content of soluble Ca2+ and Mg2+ decreased dramatically and root secreted largely p-xylene, m-xylene and DIBP especially under alkali environment. However, the release of esters decreased, and inhibited the secretion of alcohols and alkanes.Soaking seed by humic acid enhanced a-amylase activity of germinating seed, and improved root shoot ratio of seedling, promoted the accumulation of soluble sugar, enhanced sugar transportation to root, improved the ratio of sucrose to fructose in order to osmotic potential of root and enhance root absorptive capacity by strengthen of root growth.Soaking seed by humic acid enhanced the accumulation of soluble protein of seedling, decreased nitrogen tranformation and the activity of GS and nitrate reductase(NR) under salinity-alkalinity stress, however, improved the activity of SPS, SOD and catalase, increased the contwnt of soluble sugar and glutathione (GSH), enhanced elimination to oxygen free radicals, decreased lipid peroxidation. In addition, control effect of humic acid is more markedly for carbon and nitrogen metabolism and oxidation resistance of seedling under alkali stress.Soaking seed by humic acid enhanced the absorptionof K+and NSCCs, decreased the absorption of Na+ and ntercellular carbon dioxide concentration, increased the K+/Na+ of rhizosphere and stomatal conductance of leaves, improved the activation of Ca2+ and Mg2+, photosynthetic rate and absorption capacity of mineral nutrition of wheat are improved by regulating stomatal factors and rhizosphere ions balance under salinity-alkalinity stress.The study show that the harm to wheat seedling under alkali stress is stronger than that under salt stress by high pH stress as a result of CO32- hydrolyzation and damaging effects of CO32- to rhizosphere and cell microenvironment ion steady. However, soaking seed by humic acid intensify salt resistance mechanism, but control effects was influenced by genotype of wheat.