| China has a desertification area of approximately 3,327,000 km2(34%of total land area).Meanwhile,the area of desertified land is 1,739,700 km2,nearly one fifth of the land area.In recent years,desertification of the river basin soil has been worsened,althoug irrigation systems can be built and developed to protect water,but the water restriction in this region was just one of the limiting factors of its social development.Desertification as well as the poor nutrients and soil unable to retain water has severely limited the development of the region.Therefore,improving the soil is the most important issue.Photosynthetic characteristics and physiological characteristics of different growth stage(seedling,tillering,jointing)of P.giganteum z.x.lin under water stress were studied to improve the water management.At the same time,different growth stage(seedling,tillering,jointing)of P.giganteum z.x.lin under water stress were analyzed to explore its effect on soil microbial activity and Soil enzyme activity of the Brahmaputra river bank Dune,to provide theoretical support for river basin cultivation and promotion.(1)To provide the academic basis of P.giganteum z.x.lin application and popularization,physiological characteristics of P.giganteum z.x.lin under drought stress simulated by different concentration of PEG 6000 were studied.By increasing the stress level,the contents of water soluble protein and Chlorophyll decreased,showing an obvious negative correlation with PEG stress;The content of water soluble polysaccharide has increased,while the content of MDA or POD activity first increased and then decreased,the contents of proline and SOD activity first decreased and then increased.These five indices showed a significant positive correlation with PEG stress;The CAT activity first increased and then decreased,showing a weak positive correlation with PEG stress.These results indicate that P.giganteum z.x.lin seedlings can stand less than the concentration of 200 g.L-1 PEG and had a certain degree of drought tolerance.The interaction of three kinds of enzyme and osmatic adjustment substance(water soluble polysaccharide and proline)could be automatically modulated to avoid the damage from water drought,which may induce potential resistant ability of P.giganteum z.x.lin against drought conditions.More than the concentration of 200 g.L-1 PEG could bring P.giganteum z.x.lin seedlings severe drought stress and even death.Gas exchange parameters and chlorophyll fluorescence parameters of different growth stage(seedling,tillering,jointing)of P.giganteum z.x.lin under water stress were measured with pot-cultured method.The results show that the gas exchange and chlorophyll fluorescence parameters of different growth stage(seedling,tillering,jointing)of P.giganteum z.x.lin under drought stress follow the same trend.The magnitude of change is different under varying degrees of drought stress(seedling>tillering>jointing stage).Under soil drought stress.Net photosynthetic rate(A),stomatal conductance(Gs),transpiration rate(E),maximal fluorescence(Fm),Fv/Fm and Fv/Fo reduced,while water use efficiency(WUE)and the initial fluorescence(F0)increased with the soil drought stress degree enhancing.The intercellular C02 concentration(Ci)decreased at beginning and then increased.The contents of soluble polysaccharide and proline and MDA in seedling and tillering and jointing stage of P.giganteum z.x.lin under drought stress increased along with the increasing of drought stress degree.Under mild drought stress,the POD and SOD activity in seedling and tillering and jointing stage of P.gianteum z.x.lin with soil drought stress proceeding gradually increased;under moderate drought stress,the POD and SOD activity of seedling stage of P.giganteum z.x.lin.first increased and then decreased;while increased along in the tillering and jointing stage of P.giganteum z.x.lin with soil drought stress proceeding.Under severe drought stress,the POD and SOD activity in seedling and tillering stage of P.giganteum z.x.lin first increased and then decreased,while increased along in the jointing stage of P.gianteum z.x.lin with soil drought stress proceeding.The average value of the membership function in seedling and tillering and jointing stage of P.giganteum z.x.lin are 0.377,0.532,0.703,respectively,which represented drought resistance at different growth stages(jointing stage>tillering stage>seedling stage).(4)The results showed that the soil enzyme activity(catalase,acid phosphatase,urease,sucrase)increased with P.giganteum z.x.lin prolonged cultivation,the increasing amplitude of each soil enzymes:urease>sucrase>acid phosphatase>peroxidation catalase.In addition,with the increasing soil depth,soil enzyme showed some vertical distribution regularity.Among them,the difference of catalase activity in the vertical distribution was insignificant,while the difference of acid phosphatase,urease and invertase activity in the vertical direction was remarkable which deceased with the soil depth deeper.(5)The results show that with P.giganteum z.x.lin prolonged cultivation,the amount of bacteria and fungi and actinomycete cultured in soil tended to increase;As the soil depth increased,the amount of bacteria and actinomycete remained unchanged,while fungi tended to decrease.In addition,with P.giganteum z.x.lin prolonged cultivation,the gene copy number of Nitrogen-fixing bacteria and ammonia oxidizing bacteria and ammonia-oxidizing archaea increased dramatically,the increasing amplitude:ammonia oxidizing bacteria>ammonia-oxidizing archaea>nitrogen-fixing bacteria. |
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