Effect Of Water And Nitrogen Changes On The Relationships Between Activity Of The Key Enzymes In Relation To Carbon And Nitrogen Metabolism And Bud Bank Size In Leymus Chinensis

Leymus chinensis is a kind of perennial rhizomatous grass,which is known as alkali grass.It was often used as high-quality forage grasses because of its good palatability,high nutritional value,high drought tolerance and salinity tolerance and so on.The main factor at nature condition that influences forage yield is bud bank size of Leymus chinensis,and it is often strongly associated with soil water and nitrogen availability.Therefore,it is of vital important to investigate the relationships between the bud bunk size and water-nitrogen changes.In this paper,two-factor full factor experiment was designed to study the effects of water-nitrogen changes on aboveground functional traits（such as plant height,leaf area and specific leaf area,etc.）,the activity of the key enzymes of carbon and nitrogen metabolism and the bud bank size,the water were control W0,reduced water W-30%and increased water W+30%;the nitrogen were control 0 and applied nitrogen 10 g N·m^-2,respectively.This study can lay a fundamental basis for improving the productivity of Leymus chinensis and achieving sustainable development of grassland.The results in this paper were as follows:（1）Water addition treatment increased leaf area,aboveground biomass,belowground biomass,and total biomass by 14.54%,23.77%,23.78%,and 23.78%,respectively,while water reduction treatment decreased leaf area,aboveground biomass,belowground biomass,and total biomass by 10.37%,28.64%,18.38%,and 4.96%,respectively.Nitrogen application treatment significantly increased plant height,leaf area,aboveground biomass,and total biomass of Leymus chinensis by 19.78%,28.46%,22.69%,and 20.56%,respectively,and did not significantly increase belowground biomass.Water addition treatment markedly increased the number of axillary rhizome buds by 29.46%and had no observably effect on tiller buds,apical rhizome buds,and total number of buds.Nitrogen application treatment significantly increased tiller buds by 22.22%and had no significant effect on the number of rhizome apical bud,axillary rhizome buds and total buds.（2）Water reduction treatment increased the activity of pyruvate kinase,hexokinase,phosphofructokinase,phosphoenolpyruvate carboxylase and soluble sugar content by 49.18%,36.18%,33.09%,92.80%and 12.36%,respectively,which indicated that water enhanced the activity of carbon metabolizing enzymes and increased carbon synthesis and transport and plant osmotic pressure,thus alleviated the effect on the growth and development of Leymus chinensis.Nitrogen application significantly increased the contents of chlorophyll a, chlorophyll b,total chlorophyll,pyruvate kinase and phosphoenolpyruvate carboxylase by13.39%,31.66%,18.61%,79.39%and 99.89%,which indicated that sufficient nitrogen supply could stimulate carbon metabolism.The correlation analysis showed that after nitrogen application treatment,total chlorophyll contents was significantly negatively correlated with rhizome apical bud and total buds,and net photosynthetic rate was significantly positively correlated with rhizome apical bud;after water reduction treatment,the correlations between tiller buds and total chlorophyll content,net photosynthetic rate,intercellular CO₂concentration,transpiration rate,stomatal conductance,soluble sugar content and starch contents were weakened.（3）Water reduction treatment have reduced the activities of nitrate reductase,nitrite reductase,glutamate synthase,and glutamine synthase by 6%,20.26%,29.35%,and 38.20%,respectively,however,it increased the activity of glutamate dehydrogenase by 4.49%;the contents of soluble protein and free amino acids increased by 9.59%and 12.89%.The nitrogen application treatment significantly increased the activities of nitrate reductase,nitrite reductase,glutamate synthase and glutamine synthase by 32.99%,40.60%,40.56%and36.16%.At the same time,it has also significantly increased the soluble protein contents and free amino acid contents by 35.89%and 48.35%,which indicated that the nitrogen application treatment observably enhanced nitrogen assimilation and transport in Leymus chinensis.The correlation analysis showed that nitrite synthase in the control treatment was extremely positively correlated with the number of rhizome apical bud,and soluble protein contents was significantly positively correlated with the number of total buds;the correlations of nitrate reductase,glutamine synthase,and glutamate dehydrogenase with the number of total buds enhanced after nitrogen application treatment,and the correlation of soluble protein contents with the number of total buds weakened.After water addition treatment,the correlations between glutamate synthase and total number of buds changed from negative to positive,and the correlations between glutamine synthase and the number of total buds increased,glutamate dehydrogenase and the number of total buds showed significant negative correlations.In conclusion,the activity of the key enzymes in relation to carbon and nitrogen metabolism in Leymus chinensis and the bud bank size showed different correlations at different water-nitrogen conditions,which indicated that the activity of the key enzymes in relation to carbon could regulate the bud bank size on a large scale.The study in this paper could reveal the mechanism of how the water-nitrogen influence the Leymus chinensis grow and development,and it could lay a theoretical foundation for the enhancement of Leymus chinensis productivity.