| Leymus chinensis+Stipa grandis steppe community was converged to the Community of the Artemisia frigida+Short-grasses under continued overgrazing. During the succession process, dominant plants changed. This paper systematically investigated the reproductive characteristics of the main plants from four aspects of seed production soil seed bank., seedling recruitment and vegetative propagation. Influence of grazing on the reproductive behavior and the change of the reproductive strategy of the main plants were discussed from the angle of plant adaptation to the local environment. The main research results were as follows:1. The research sites were selected in a Leymus chinensis+stipa grandis steppe community (Site A) and a Community of the Artemisia frigida+Short-grasses (Site B). The plants that can reach flowering/seeding stage and the seed yield in fenced plot exceeded over unfenced plot in site A. The influences of grazing on the flowering and seeding of the key plants were difference. After grazing, the rate of flowering tillers was decreased, and the rate of seeding was unchanged or increased. In site B, the rates of flowering and seeding consistently increased at beginning and then decreased with grazing intensity increased. The seed yields were difference at the two sites. Seed yield at site B was higher than at site A. The differences of seed yields were also occurred in different years influenced by precipitation in the previous year and the seasonal distribution of precipitation in the current year.2. Seed germination abilities in different plants were different in terms of germination percentage and germination duration. Both the time of seed maturation and seed dormancy/germination behavior determines the seedling emergence.3. In the fenced plot of site A, the seed percentage of annual and biannual herbs in soil seed bank reserve was very high, and the percentage was even higher in the unfenced plot. Due to decreased seed input and increased accumulative seedling output, the seed bank reserve shrunken with the sampling time postponed. The percentage of the seeds of annual and biannual herbs in all plots of site B was lower than those of site A, and the change of seed bank reserve was inconsistent in different plots of site B. Under the heavy grazing, the seeding of plants was affected and the seed number in soil was the least.The correlation between aboveground vegetation and the seed composition in soil in site B was lower than that in site A. The correlation was attributed to the three types of plants: (1) the ephemerals plants; (2) the plants that had the transient soil seed bank or the aerial seed bank; (3) the plants of mainly vegetative propagation.The most of seeds in the soil concentrated in the 0-5 cm of the soil surface in typical steppe. The patchy distribution of seed cohort in site B was more evidence than that in site A.4. Although the quantity of seedlings in fenced plot of site A was bigger than that in unfenced plot, the life form of seedling cohort became simplified and the diversity was reduced. Annual and short-lived species tended to increase. The quantity of seedling was high at low grazing intensity and decreased with increased grazing intensities in site B. Dominant plants were similar under different stocking rates.The times of seedling emergency in different plants were different. On the whole, seed germination goes through a remarkably regular cycle, with two peaks of emergence occurring, the distribution of raining would restrict one of peaks. The quantities and the dominant plant species of seedlings were difference in years, which was resulted from the interaction of the seasonal distribution of raining with the time of seedling emergence and that was one adaptive behavior of the plants. Given sufficient water, the quantities of seedling increased sharply, especiallythe annual plant, but species composition unchanged. Drought, competition, and browsing or trampling of animals were the mostly common factors contribut...
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