Abstract:

In this study， stands of Elymus sibiricus cv. Qingmu No.1 （which is widely distributed and used in the grasslands of Qinghai Province on the Qinghai-Tibetan plateau） were studied. Three field experiments were set up； namely the normal growth over years one to six from establishment of Qingmu No.1 without fertilizer application， the effect of fertilizer addition to six year old stands and annual fertilizer application over the six year experiment. The aboveground biomass and characteristics relevant to seed production or plant growth， such as specific leaf area were recorded and the effect of fertilizer in the two fertilizer treatments were analyzed. It was found that the aboveground biomass increased from one to three years old and peaked at two-three years old， and then decreased from three years old onwards. We identified four developmental stages over the six-year experiment period： in the first year the initial growth and establishment stage； at two-three years old， the maximum biomass stage； at four-five years old， the decline stage and at six years old and beyond， the aging stage. The single ear weight increased year by year up to five years of age then decreased significantly in the sixth year. The ear dry weight as a proportion of above ground biomass showed the same trend as the single ear weight. In six year old plots of E. sibiricus， nitrogen and phosphorous addition increased the aboveground biomass significantly compared with the control treatment， and the effect of nitrogen was greater than the effect of phosphorous. The biomass of six year old E. sibiricus stands was much higher with the addition of 75 kg·ha^-1 N than at lower rates of N. With the addition of 60 kg·ha^-1 N the single ear weight was much higher than at higher or lower rates of N. With annual fertilization， the aboveground biomass was significantly higher than the control which received no fertilizer. The aboveground biomass was highest under a treatment receiving 60 and 75 kg·ha^-1 of N and P， respectively， and the single ear weight was highest under a treatment receiving 75 kg·ha^-1 of both N and_{P （N75P75）. The proportion of stem in the aboveground biomass increased year by year from year two to year six without fertilizer addition. Under an annual fertilizer addition of 45 kg·ha^-1 N and 90 kg·ha^-1 P， the proportion of stem was decreased， and the proportion of ear and leaf was significantly increased. Long-term fertilizer addition treatments of 60 and 90 kg·ha^-1 of N and P， respectively， and N75P75 also had enhanced the ratio of ear effectively.}

Key words: Elymus sibiricus, ageing, phenotypes, reproduction strategy, nutrient addition