Effects Of Rainfall Change And Nitrogen Deposition On Carbon Allocation And Bud Bank Construction Of Leymus Chinensis

In recent years,global changes,represented by changes in rainfall and nitrogen deposition have intensified year by year.Nitrogen and water are the two most critical factors that limit the growth and development of grassland plants in semi-arid regions,and their changes will inevitably affect grassland ecosystems.Leymus chinensis,as one of the important forage grasses in the grasslands of Northeast of China and Inner Mongolia,has the characteristics of rapid growth,strong stress tolerance and rich nutritional value.As a typical clonal plant,L.chinensis,mainly reproduces asexually,and the change of its aboveground population density depends on the bud bank attached to the underground rhizome,and is strongly driven by water and nitrogen factors.The regulation mechanism of bud bank construction has important practical value for improving the productivity and quality of L.chinensis.In this study,a two-factor full factorial experimental design method was used,and two factors,nitrogen（N⁺with nitrogen application,N^-without nitrogen application）,and moisture（normal rainfall R⁰,30%increased rainfall R⁺,and 30%decreased rainfall R^-）were set.The stable isotope ¹³C tracing method,firstly studied the contribution of carbon synthesized by L.chinensis in different periods to the construction of the Leymus chinensis bud bank,secondly,the influence of rainfall changes and nitrogen deposition on the L.chinensis carbon allocation,and finally the effect of carbon allocation of L.chinensis organs under sedimentation on the construction of L.chinensis bud bank,the main results are as follows:1)With the increase of rainfall,the total biomass of L.chinensis gradually increased,the decrease of rainfall significantly reduced the total biomass of L.chinensis by 24.04%,and the increase of rainfall significantly increased the total biomass of L.chinensis by 25.02%.The proportion of biomass under the L.chinensis decreased significantly,and the root-shoot ratio decreased accordingly.Nitrogen fertilization significantly increased the total biomass of L.chinensis by18.32%,but decreased the distribution ratio of underground biomass and significantly decreased the root-shoot ratio by 24.58%.The decrease of rainfall decreased the net photosynthetic rate of L.chinensis by 13.87%,and the increase of rainfall and nitrogen application increased the net photosynthetic rate of L.chinensis by 10.96%and 8.71%.The ability of photosynthesis is enhanced,and more photosynthetic products will be accumulated in L.chinensis,so the biomass of L.chinensis will increase.2)Decreased rainfall significantly increased the proportion of ¹³C carbon allocation marked in seed maturation stage and early post-fruiting vegetation stage in the lower roots of Leymus L.chinensis by 29.27%and 22.18%.The ¹³C allocation ratio marked in early post-fruiting vegetation stage decreased significantly by 23.19%;nitrogen application significantly increased the ¹³C allocation ratio of L.chinensis stems marked in flowering stage,seed maturation stage and early post-fruiting vegetation stage by 36.80%,20.98%and 22.41%,but decreased the ¹³C allocation ratio of L.chinensis in flowering stage,seed maturation stage and early post-fruiting vegetation stage.Part of the carbon allocation ratio,indicating that under drought conditions,L.chinensis will put more carbon resources into the underground part and absorb more water and nutrients from the soil,while under the conditions of sufficient rainfall and good nutrient resources,it can be reduced.The uptake burden of the underground part of the plant will put more carbon resources into the above-ground stems and leaves for higher photosynthetic performance and productivity.3)With the increase of rainfall,the number of bud banks of L.chinensis gradually increased.When the rainfall increased,the number of rhizome node buds and rhizome terminal buds of L.chinensis increased significantly by 8.95%and7.70%,respectively.Nitrogen application also significantly increased the total number of L.chinensis,tiller buds and rhizome terminal buds by 8.80%and 11.67%,respectively.And by the method of stable isotope¹³C tracking,it was found that the abundance of ¹³C labeled in June,July and August in the L.chinensis bud library was different.Among them,the abundance of¹³C marked in early post-fruiting vegetation stage was the highest in the L.chinensis bud bank,indicating that the photosynthetic products synthesized in early post-fruiting vegetation stage contributed significantly to the construction of the L.chinensis bud bank than in flowering stage,seed maturation stage.The photosynthesis performance in the middle and late period regulates the production of buds and daughter plants at the end of the growing season,stores more energy,and contributes to the expansion of the L.chinensis population and the improvement of productivity when it turns green in the second year.4)Through the correlation analysis between the number of L.chinensis bud banks and the carbon allocation ratio of each organ of L.chinensis,it was found that the number of L.chinensis bud banks was negatively correlated with the carbon allocation ratio of some organs in L.chinensis,and was mostly related to the underground roots and rhizomes of L.chinensis.positive correlation.Among them,tiller buds are more easily regulated by carbon allocation than rhizome terminal buds and rhizome node buds,and nitrogen application enhances the negative correlation between the¹³C allocation ratio marked in flowering stage,seed maturation stage and early post-fruiting vegetation stage in L.chinensis stems and the number of tiller buds of L.chinensis（R=-0.997;R=-0.999;R=-0.975,P<0.05）,which weakened the positive correlation between the carbon allocation ratio in roots and rhizomes and the number of L.chinensis bud banks.The decrease in rainfall enhanced the positive correlation between the distribution ratio of ¹³C marked in seed maturation stage in roots and rhizomes and the total number of bud banks of L.chinensis（R=0.995;R=0.962,P<0.05）.To sum up,rainfall changes and nitrogen deposition can not only regulate the composition and quantity of bud bank by affecting the biomass allocation and photosynthesis capacity of L.chinensis,but also regulate the composition and quantity of bud bank by adjusting the carbon allocation ratio of each organ in L.chinensis.The changes of nitrogen application and rainfall were important factors affecting the correlation between the carbon allocation ratio in abovegroung stems,underground roots and rhizomes of L.chinensis and the number of L.chinensis bud banks.Moreover,in the construction of L.chinensis bud bank,the contribution of photosynthetic products synthesized in early post-fruiting vegetative stage is much greater than that of photosynthetic products synthesized during flowering stage and seed maturation stage,indicating that at the end of the growing season when a large number of buds are produced,newly synthesized photosynthetic products the contribution to the construction of the bud library is relatively large.This study helps to understand the regulation mechanism of L.chinensis carbon allocation on the L.chinensis bud bank,and provides a theoretical basis for the improvement of grassland productivity and sustainable grassland management in the future.