Seedling Recruitment In Response To Mowing And Grazing In Typical Steppe Community In Inner Mongolia, China

Seedling is the main resources which plant population renews. Many natural grassland plants may carry on vegetative propagation,but the plant sexual reproduction characteristic actually is necessary to population which adapts to circumstances or environment, maintains own sustainability. Seedlings are produced from the same year seed rain or the soil seed bank. Recruitment of seeds directly reflects seedling species composition and the quantity.Theoretically speaking, seedling is central to population maintenance, community structure and succession. But the dynamics of seedling recruitment of perennial grassland especially in typical steppe is still unclear. Moreover, the responses of seedling dynamics to different disturbances such as mowing and grazing in Eurasian typical steppe ecosystems have been scarcely studied before.In order to study the effect of mowing and/or grazing on the seasonal dynamics of three dominant gramineous seedlings emergence, survival and mortality in typical steppe communities, this experiment was established the different gradient mowing and grazing treatments during April to November in 2006 and monitored communities' superiority status, population's reproduction assignment, vegetation's characteristic attribute as well as seedling dynamics of each kind of plant under these treatments in investigation quaudrat. Simultanously, three dominant gramineous seedlings including Stipa krylovii, Cleistogenes squarrossa, Agropyron cristatum were classified and statistically processed. Through each community index as well as external environment condition change analysis such as water and temperature, following conclusions were drawn out:1. Regular mowing usually implemented in late August had negative effects on the seedling density especially for tall growing species. However, for short growing species, mowing might be a facilitating agricultural measure.2. Seedling densities of all the three species basically increased from late-May to mid-August. Mowing suppressed seedling emergence of tall-growing Stipa krylovii by affecting seed availability due to reproductive parts removal when mown in the previous year, whilst exerted a positive effect on low-growing Cleistogenes squarrossa probably as result of increased light availability and less competitive pressure from adult individuals, because mowing largely lowered the vegetation height and density.3."U"shaped curve for seedling mortality across the entire growing season was thought to be associated with seasonal changes of air temperature but a small peak from mid-June to early July could probably be attributed to drought due to previous rainfall shortage.4. Seedling emergence took place fairly synchronously from May to July, especially from mid to late July, probably due to the relatively optimum environmental conditions. Seedling emergence was related to dormancy of seeds.5. In addition, seedling survival or establishment was considered related to the size and morphology of the seeds, which remained to be ascertained. Furthermore, soil substrate also played an import role in seedling establishment.