Effects Of Rainfall Changes And Nitrogen Addition On The Unstructured Carbohydrate And Stoichiometric Characteristics Of Reaumuria Soongorica Seedlings

In recent years,with the acceleration of industrialization and urbanization,the massive combustion of fossil fuels leads to a sharp increase in nitrogen deposition,and global climate change leads to the frequent occurrence of extreme droughts and floods,which has become a major environmental problem.The change of rainfall pattern and the increase of atmospheric nitrogen deposition,as the two major factors of global change,have a great impact on the global ecosystem,especially in the desert ecosystem.Non-structural carbohydrates as the main product of plant photosynthesis,the changes not only reflect the dynamic balance of plant carbon acquisition and spending,and further affect the plant growth and adaptation to the environment changes,thus to explore the rainfall change and adding nitrogen on plant growth and the influence of the accumulation and distribution of non-structural carbohydrates is of great significance.In this study,1-year old Reaumuria soongorica seedlings were taken as the experimental object to study the effects of different rainfall?decreased rainfall?W-?,natural precipitation?W?and increased rainfall?W+??and nitrogen added(N₀(0g N?m^-2·a^-1)?N₁(4.6g N?m^-2·a^-1)?N₂(9.2g N?m^-2·a^-1)?N₃(13.8 gN?m^-2·a^-1))on the non-structural carbohydrate distribution and dynamic characteristics of R.soongorica seedlings.Meanwhile,the response mechanism of R.soongorica seedlings to rainfall change and nitrogen deposition was clarified by combining the growth of red sand seedlings and the changes of organic carbon,total nitrogen and total phosphorus contents.The research results and conclusions are as follows:?1?Increased rainfall and appropriate nitrogen addition promoted the growth of each organ and dry weight accumulation of biomass in R.soongorica seedlings;at the end of the growing season,the biomass of coarse roots decreased by 44.04%,14.43%,and 13.00%under different water conditions compared with that under medium nitrogen?N₂?plus high nitrogen?N₃?plus,indicating that the growth of coarse roots of R.soongorica seedlings was inhibited by long-term excessive nitrogen addition.when water was sufficient?W and W+?,the maximum plant height growth amount was 14.4cm and 13.83cm under the addition of high nitrogen?N₃?,which increased by30.91%and 38.97%compared with the control,while when water was insufficient?W-?,the plant height growth under the addition of high nitrogen was 28.46%less than that under the control,indicating that the interaction between water and nitrogen had a certain coupling effect on the growth of R.soongorica seedlings.?2?In the case of sufficient water?W+?,nitrogen addition promoted the accumulation of soluble sugar,starch and non-structural carbohydrate contents in the leaves of R.soongorica seedling.the content of non-structural carbohydrates in fine roots increased first and then decreased with the increase of nitrogen content,and the high nitrogen addition was 25.11%less than the low nitrogen addition,indicating that excessive nitrogen addition had an inhibitory effect on the accumulation of non-structural carbohydrates in fine roots of R.soongorica seedlings;Under drought stress at the end of the growth season,soluble sugars in leaves,stems and coarse roots increased with the increase of nitrogen content after nitrogen addition?N₁-N₃?,increasing by 21.25%,25.41%and 41.54%at the high nitrogen?N₃?,while starch content decreased by 25.82%,12.00%and 13.21%at the N₃,and the soluble sugar and starch content of fine roots also showed the opposite trend.It indicates that the R.soongorica seedlings can adapt to the change of external environment by the mutual transformation between soluble sugar and starch to cope with the stress conditions.?3?The NSC contents of leaves,fine roots and coarse roots decreased first and then increased with the passage of the growing season.The NSC accumulation of leaves and fine roots reached the maximum in the early period of the growing season,which were 35.25mg?g^-11 and 31.25mg?g^-1,in the early part of the growing season,the leaf photosynthesis was in the best state,and the fine roots absorbed a large number of nutrients,and the energy accumulation was greater than the energy consumption;the coarse roots were used as storage organs and the NSC accumulation reached a maximum of 53.00mg?g^-11 in the late growth season;the content of stem NSC remained at 24.00mg?g^-126.75mg?g^-11 with the development of the growing season,with little change,indicating that R.soongorica seedlings tended to maintain the stability of stem NSC.?4?The soluble sugar content of each organ of R.soongorica seedling was4.46mg?g^-129.85mg?g^-1,the soluble sugar content in the later growth season was coarse roots>fine roots>leaves>stem,indicating that the R.soongorica distributed more soluble sugar in the underground root part to maintain its growth;The starch content of each organ of the R.soongorica seedling was 7.09mg?g^-135.21mg?g^-1,the starch content of coarse roots was always the highest throughout the growing season,indicating that coarse roots were the most important storage organ of starch in R.soongorica seedlings;R.soongorica seedling organs NSC content is 18.77mg?g^-159.11 mg?g^-1,among them the most content of coarse roots,followed in the leaves,fine roots,stems,the leaves is second only to that of the coarse root,the leaves carry out photosynthesis and have stronger carbon assimilation capacity,which is the NSC source of the whole tree.?5?The changes of rainfall and nitrogen deposition had no effect on the organic carbon content in the leaves of R.soongorica seedlings,and the organic carbon content was stable in the leaves of R.soongorica seedlings.Under the treatment of reduced rainfall and natural rainfall,the increase of nitrogen content leads to the decrease of nitrogen in roots,because the root activity is reduced at the end of the growing season,and nitrogen absorption is reduced,on the other hand,the nitrogen absorbed by plants is converted and used in physiological processes such as plant organ building to help the R.soongorica seedlings survive the winter.Under the treatment of W+N₃,the total phosphorus content of roots reached a maximum of7.22%,and after the addition of nitrogen,the total phosphorus content of roots showed an increasing trend with the increase of nitrogen content,and the increase was more obvious under the condition of abundant water,indicating that the total phosphorus content in roots of R.soongorica seedlings was affected by the interaction between rainfall and nitrogen.