| Elymus sibiricus L.,belongs to the genus of Poaceae,is an important species in the alpine region of the Tibetan Plateau and even in the steppe region of northern Eurasia.It has many excellent characteristics and plays an important role in the improvement of degraded grassland and livestock breeding.However,the problems of declining population stability and yield reduction occur with increasing years of planting,which is the main bottleneck that causes the Elymus sibiricus can not be planted in a large area for a long time.Therefore,this study selected "Qing mu No.1" Elymus sibiricus with different planting years(3,4 and 5 years)as the object.The productivity change,anatomy structure change,plant microscopic and ultrastructural changes and the photosynthesis of different years were mainly studied.Through the above research,the following important results have been obtained:(1)Growth years had a significant effect on grass and seed yield and its stability,hay yield and seed yield composition traits.With increasing growth years,the fresh grass and hay yield of E.sibiricus showed a decreasing trend,in which the fresh grass yield of 3-year-old E.sibiricus was the largest and higher than 4 and 5 ages about34.22% and 52.45%,respectively while the hay yield decreased significantly by22.88% and 39.35%.And the seed yield of E.sibiricus showed a decreasing trend,which of 4 and 5-year-old decreased 34.22% and 52.45% than 3-year-old respectively.Moreover,the seed yield of E.sibiricus showed a decreasing trend with increasing growth years,which of 4 and 5-year-old decreased of 12.72% and 34.17% than 3-year-old,respectively.The stability of hay yield and seed yield of E.sibiricus deteriorated with increasing growth years.The hay yield components of plant height,stem thickness,total number of tillers per unit area and fresh weight per plant all showed decreasing trends with increasing growth years.There were extremely significant correlations between yield and fresh weight per plant.Furthermore,the seed yield component traits of spikelets per reproductive branch,thousand seed weight,and number of reproductive branches per unit area all showed decreasing trends with increasing growth years.It showed extremely significant correlations between seed yield and seed 1000 weight.(2)The crude protein(CP)content of the same age E.sibiricus showed a decreasing trend with the development of phenological stage,while the CP content of the same phenological stage showed a decreasing trend with the increase of growth years.The acid detergent fiber(ADF)and neutral detergent fiber(NDF)showed the opposite trend to those of crude.The relative feed value(RFV)content of 3-year-old E.sibiricus was the highest than that of 4 and 5-year-old at the first and full flowering stage reached for 163.18 and 143.95 and was significantly higher than that of 4 and5-year-old E.sibiricus with 13.36%、38.29% and 12.93%、39.85% at the same period(P < 0.05).According to the comprehensive evaluation of nutritional value in different growth stages of the same age and different growth stages of the same age,the order of nutritional values were as follows: 3-year-old at first flowering >3-year-old at full flowering > 4-year-old at first flowering > 5-year-old at first flowering > 4-year-old at full flowering > 5-year-old at full flowering > 3-year-old at ripening stage > 4-year-old at ripening stage > 5-year-old at ripening stage.(3)The photosynthesis environment and photosynthesis parameters of E.sibiricus varied among different growth years at different phenological stages.In the same phenological stage,the height of E.sibiricus decreases with increasing growth years.The leaf length and leaf area of the flag leaf of E.sibiricus 4-year-old reached the maximum and differed significantly(P < 0.05)from those at the age of 3 or5-year-old.The factors responsible for photoinhibition E.sibiricus leaves differed among growth years,the main factor was stomatal restriction at the elongation and flowering stages and non-stomatal factors at the ripening stage.(4)The effects of different growth years on the leaf,stem and root anatomy of E.sibiricus were greater.3-year-old E.sibiricus leaves had dominant stable variation in midvein vascular bundle width,midvein prominence,lower epidermal thickness and leaf thickness.Their mean values were higher than the corresponding overall(3,4 and5-year-old)and the mean values and the coefficients of variation were lower than the corresponding overall coefficients of variation by 39.78%,48.76%,20.92% and77.63%,respectively.It is beneficial to improve cold and drought resistance.Similarly,the posterior xylem duct height and duct width traits of 4-year-old E.sibiricus leaves were the dominant stable variation.The coefficient of variation was lower than the overall coefficient of variation by 27.45% and 17.87%,respectively,which benefits to the efficient transport of water and nutrients in the leaves.5-year-old E.sibiricus leaves had inferior unstable variation in midvein vascular bundle height and width,upper epidermal thickness and leaf thickness.3 and4-year-old E.sibiricus had more functional infrastructure for stem transport(number of large and small vascular bundles,total area,mechanical tissue and thin wall tissue thickness)than 5-year-old E.sibiricus plants in terms of the effective water transport structure of the roots of 5-year-old E.sibiricus were inferior in both number and total area.The transport capacity of 5-year-old E.sibiricus roots was poorer than that of 3and 4-year-old,as evidenced by the fact that the total area of posterior xylem ducts and the ratio of mid-column area to root cross-sectional area of roots were significantly lower than that of 3 and 4-year-old E.sibiricus.(5)Different growth years had a greater impact on the ultrastructure of E.sibiricus leaves,and the typical phenomenon of programmed cell death(PCD)was accompanied by the process of leaf senescence.At flowering stage,the effect of growth years on the stacking and arrangement of the basal lamellae in the chloroplast was more obvious.The lamellae of the basidiomata gradually loosened and distorted with increasing growth years,and even some of the lamellae structures disappeared.With the increase of growth years,the number of hungry particles in chloroplasts showed an increasing trend.The disintegration of chloroplasts of E.sibiricus leaves began to occur at ripening stage,and the degree of disintegration became more and more intense with the increase of growth years.At ripening stage,the nuclei were observed to have the typical phenomena of programmed cell death,such as the marginalization of solidified chromatin.It proved that senescence of E.sibiricus leaves was controlled by cell programmed and was a spontaneous death state.The earlier the initiation of programmed cell death in E.sibiricus leaves with the increase of growth years,the earlier the initiation of programmed cell death in E.sibiricus leaves.In general,with the increase of plant age,the grass yield,seed yield,stability and composition of the E.sibiricus decreased,and also the nutritional quality decreased gradually.The leaves showed obvious programmed death characteristics.In particular,the above characteristics of the 5-year-old E.sibiricus changed most obviously.It could be concluded that the 3 to 4-year-old were the key period for the growth of E.sibiricus and it is of great significance to delay the grassland use years by regulating it in this period. |
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