Responses Of Carbon And Nitrogen Metabolism Of Masson Pine Seedlings To Drought And Post-drought Rewaterin

Carbon metabolism provides a carbon skeleton for plant growth,maintains cell osmotic potential,and can use stored non-structural carbohydrates to provide a temporary carbon source.Carbon metabolism may also participate in the repair of xylem embolism after rehydration.Nitrogen metabolism provides photosynthetic energy for carbon metabolism,and the interaction between the two can significantly improve the drought resistance and recovery ability of seedlings.At present,the plant metabolism of carbon and nitrogen concentration on the grass and crops,less research on woody plants,now mainly concentrated in the United States,Europe,the broad leaved tree species,and the C and N content in view of the whole plant or a single organ change are studied,on the C and N photosynthate between different organs change characteristics and key enzyme activity changes in response to drought is unclear,Nor is it clear how carbon and nitrogen metabolism respond to rehydration.Therefore,this research through pot experiment,for 1 year 5 months to natural Pinus massoniana seedlings drought treatment and different degree of dry after water treatment,system research of the root,xylem and phloem,carbon and nitrogen in the leaves and stems of photosynthate and seedling carbon and nitrogen metabolism of key enzymes response characteristics of the complex water after the drought and drought,revealing the Pinus massoniana seedlings after the carbon and nitrogen metabolism in drought and drought after the response mechanism of the water,To provide scientific basis for drought resistance and rehydration response mechanism of Pinus massoniana semi-arid and arid areas.The following results were obtained:1.With the increase of drought,the initial quantum efficiency(α),maximum net photosynthetic rate(Pn max),light saturation point(Ls,P)and dark respiration rate(R_d)of Pinus massoniana seedlings decreased by 86.84%,80.92%,50.16%and 34.30%,respectively,leading to the decrease of light use efficiency.The dry matter accumulation was inhibited,but the total root length,average diameter,surface area and volume of seedlings increased when the drought degree was low,and the growth was inhibited when the drought degree was deepening.2.The activities of SPS,ADPGPPase,NR and GS in Pinus massoniana seedlings increased at first and then decreased with the extension of drought time and the deepening of drought degree,while the contents of fructose,glucose-sugar and soluble sugar in roots,xylem,phloem and leaves and C:N in xylem increased at first and then decreased.The contents of sucrose,NSC,nitrogen in root and phloem increased.Starch increased continuously in xylem and phloem,and increased first and then decreased in leaf.The contents of sucrose and soluble sugar/starch in leaves increased first and then decreased,and were significantly lower than those in the control at 75 d.Comprehensive shows that drought key regulating carbon and nitrogen metabolism enzyme activity of synthesis of needles in the soluble sugar cane sugar,decomposition and nitrogen assimilation capacity,increase the xylem and phloem,the root of the NSC content and nitrogen content to increase drought resistance,but increased drought degree of Pinus massoniana seedlings will more NSC distribution of roots in response to drought.3.The content of SC used for root morphogenesis was significantly different with the extension of drought time.Among them,lignin and SC contents in roots increased first and then decreased,cellulose contents increased,stem lignin contents increased,and leaf lignin and SC contents decreased,indicating that Pinus massoniana seedlings can enhance the mechanical strength and hydrophobicity of the aboveground part by regulating the changes of SC contents and components in various organs.And regulate the cellulose content of underground part to promote root elongation and improve the drought resistance ability of Pinus massoniana seedlings.4.After rehydration,the root,xylem,phloem soluble sugar and NSC of P50 and P85 were preferred to the control level of leaves.The starch content in leaves decreased significantly with the prolongation of rehydration time,while the soluble sugar and soluble sugar/starch increased significantly.However,the starch content in xylem and phloem did not show significant differences with the prolongation of rehydration time.After rehydration,the activities of SPS,ADPGPPase and NR in P50 all recovered to the CK level after 7 days of rehydration,while the activities of SPS,ADPGPPase,NR and GS in P85recovered to the control level after 15 days.Studies showed that the starch in the middle of Pinus massoniana seedlings acted as a temporary carbon source during the rehydration process,providing osmotic substances for the recovery of seedling metabolism.The recovery ability of carbon metabolism was higher than that of carbon metabolism,but the recovery degree was related to the degree of drought suffered by the seedlings.