Research On Physiological And Biochemical,Carbon And Nitrogen Metabolism Characteristics Of Elymus Sibiricus L.with Different Growth Years

Belongs to the genus Elymus of Poaceae,Elymus sibiricus has many excellent characteristics,and also plays an important role in the improvement of degraded grasslands and the grass cultivation and livestock breeding.Therefore,it's an important constructive species in the Qinghai-Tibet Plateau and even in the steppe of northern Eurasia.However,many experiments had proved that the biggest disadvantages of E.sibiricus is its short usage limit,which directly prevented it from being planted in large area for a long time.To explore the physiological and biochemical mechanisms and the characteristics of carbon and nitrogen regulation affecting the gradual decline of E.sibiricus population,and to lay a theoretical foundation for delaying the senescence initiation of E.sibiricus or the selection of anti-aging techniches,with E.sibiricus cv.Qingmu No.1 of different planting years?3,4 and 7?as materials,the endogenous hormone content,oxygen radical production rate,malondialdehyde content,antioxidant system and carbon-nitrogen metabolism in various organs of E.sibiricus with different planting years s in two consecutive years were studied.The results are as follows:?1?The key indicators of the antioxidant system including superoxide dismutase?SOD?activity,O^2-production rate(O^2-)and malondialdehyde?MDA?content had greater impacts on the stability of E.sibiricus population.With the planting year grows,the SOD activity in leaves and roots of E.sibiricus decreased gradually,whereas the O^2-production rate and MDA content increased gradually.For the SOD activity in different organs and growth stages under the same planting year,leaves changed more obviously than roots and stems,as well as heading stage than other growth stages.Compared with 2018,the SOD activity in leaves of 3,4 and 7 years plants at the heading stage in 2019 decreased by 86.73%,85.86%and 81.15%,respectively.The O^2-production rate and MDA content increased with the aging of E.sibiricus.In terms of different organs,the effect of plant age on the O^2-production rate in roots of E.sibiricus was greater than that on leaves and stem sheaths,and that on MDA content in stem sheaths was greater than that on leaves and roots.The MDA content in stem sheaths at the jointing stage and booting stage of E.sibiricus enhanced the most in 7 and 8 years plants,with each increased by 89.54%and 318.11%,respectively.?2?The contents of endogenous hormone such as abscisic Acid?ABA?and gibberellin?GA?in E.sibiricus varied greatly in different planting years.The ABA content in leaves of 4 and 7 years E.sibiricus in 2019 increased the most,with each reaching 96 times and 3 times that in 2018.The GA content of E.sibiricus increased firstly and then decreased,especially in roots.?3?In the process of carbon metabolism,the activities of sucrose synthase activities?SS?and sucrose phosphate synthase?SPS?in leaves and roots of E.sibiricus at the same growth stage generally increased first and then decreased with plants age,however,the soluble sugar content increased gradually.In the process of nitrogen metabolism,the total N content in leaves and stem sheaths decreased gradually with plants age,whereas the activities of nitrate reductase?NR?and glutamine synthetase?GS?increased firstly and then decreased.For different organs at the same growth stage,the effect of plant age on the nitrogen metabolism of leaves was greater than that of stem sheaths.Compared with 2018,the total N content in leaves of 4,5 and 8 years plants at the jointing stage in 2019 decreased by 37.14%?30.43%and 25.00%,respectively;that at the booting stage decreased by 39.29%?14.29%and 33.33%,respectively;that at the heading stage decreased by 56.67%?38.89%and 41.18%,respectively.?4?Based on the principal component analysis,it was found that leaves and roots had greater influences on the stability of E.sibiricus population than stem sheaths.The accumulation of carbon and nitrogen as well as the balance between O^2-and SOD were the main factors affecting the stability of E.sibiricus population.Overall,with the increase of the growth years of E.sibiricus,the total N,SOD activity and GA content decreased gradually,while the MDA,ABA content and O^2-content increased gradually,and the assimilation efficiency of carbon and nitrogen increased at first and then decreased at the inflection point of 4 years old.