Effects And Mechanism Of Increasing Nitrogen And Reducing Water On Growth Strategies Of Herbaceous Plants In Broad-leaved Korean Pine Forest

Increasing nitrogen deposition and changing precipitation patterns are subtly affecting the entire ecosystem of Changbai Mountain.As the main component of the understory,herb plants are extremely sensitive to environmental stress and have high potential sensitivity to nitrogen deposition.For most trees.And herbaceous plants play a positive role in forest regeneration and the growth and development of tree seedlings to a certain extent;they can also control the soil erosion of the forest and maintain the sustainable development of the forest.Therefore,in order to explore the effects of nitrogen deposition and climate change on herbaceous plants,this experiment carried out experiments to simulate nitrogen deposition and rainfall reduction in the broad-leaved Korean pine forest area of Changbai Mountain.Four treatments were designed,namely,nitrogen increase(N+)and water reduction.(W-),increase nitrogen and reduce water(N+W-),control(CK).Under different treatments,five herbaceous plants were selected,and their biomass,carbon(C),nitrogen(N),phosphorus(P),C:N and N:P,and root morphological traits were determined.The relevant results of the study are as follows:(1)Appropriate nitrogen addition is beneficial to the growth of herbaceous plants,which is mainly reflected in the significant increase in the biomass of herbaceous plants.Moreover,the addition of an appropriate amount of nitrogen can alleviate the effects of mild drought stress on herbaceous plants.Among them,under the treatment of increasing nitrogen,deer medicine mainly distributes the biomass to the above-ground part,the biomass of the underground part is significantly reduced(P<0.05),and the root-to-shoot ratio is significantly reduced(P<0.05).The biomass of roots,stems,and leaves of P.mongolica increased significantly under the nitrogen-increasing treatment(P<0.05).Under the nitrogen-increasing treatment,the mosquito grass mainly distributes nutrients to the stems,which greatly increased the biomass of the stems.During this process,the biomass of leaves and roots did not change significantly.Under the treatment of increasing nitrogen,the biomass of roots did not change significantly.The biomass of leaves and stems increased significantly(P<0.05),and the ratio of root to shoot decreased significantly.(P<0.05).Under the treatment of increasing nitrogen in Beizhonglou,the stem biomass decreased significantly,and the leaf biomass also showed a decreasing trend,but it did not reach a significant level.The root biomass showed an upward trend,but did not reach a significant trend.Crown ratio increased significantly(P<0.05).(2)Under water reduction treatment,different herbs adopt different growth strategies.Deer medicine and mosquito grass adopt an active and rapid nutrient acquisition strategy,while Shan Jianzi,Shan eggplant,and Beizhonglou adopt relatively conservative strategies.(3)The biomass allocation strategy of herbaceous plants is different under the treatment of increasing nitrogen and reducing water.Under the treatment of increasing nitrogen,most herb plants tend to allocate biomass to the leaves and stems;under the treatment of reducing water,the biomass of herb plants tends to be allocated to the above-ground part,although the change in biomass is not significant.(4)Under different treatments,the change of C concentration in various organs of herb plants is not as large as the change of N and P concentration.Under the treatment of increasing nitrogen,the change trend of N concentration of herb plants is basically the same,and all of them are leaf nitrogen.The most content.The P concentration of each organ of herb plants responds differently to different treatments,and some have higher P concentration in leaves,and some have higher P concentration in roots.It shows that there are organ differences in the P concentration of different herbs.(5)In this experiment,the N:P of different herb plants and different organs did not exceed 16,which shows that the herb plants in the experimental plot are still restricted by N.Since the C content of herb plants is relatively stable under each treatment,the change of C:N is mainly affected by the change of N.(6)Under the treatment of increasing nitrogen,the specific root length and specific surface area of herbaceous plants decreased significantly(P<0.05)or did not decrease significantly,indicating that the root morphology will change with the change of soil nutrients.When exogenous nitrogen When added,the nitrogen in the soil will increase,and the higher-order roots of plants will absorb more carbon to improve the efficiency of carbon use.Under water reduction treatment,the specific root length of different herbs has different changes,and the indicative difference of fine root specific root length to environmental changes is considered to be the response between species.Under the treatment of increasing nitrogen and reducing water,the addition of appropriate amount of nitrogen alleviated the adverse effect of water reduction on root morphology.In summary,it can be found through simulated nitrogen deposition and precipitation reduction experiments that the nutrient distribution and growth strategies of herbaceous plants have changed.Therefore,understanding the changes of herbaceous plants will help supplement the theoretical research of the temperate broad-leaved Korean pine forest ecosystem and provide theoretical and data support for forest conservation and sustainable management in Changbai Mountain.