[Seedling regeneration and affecting factors of Quercus variabilis in different distribution regions]

Twenty four fixed plots in three distribution regions of Quercus variabilis (Loess Plateau, marginal distribution zone; north slope of Qinling Mountains, semi-arid core area; and south slope of Qinling Mountains, moist core area) were installed, respectively, to investigate the age structure, growth status, and dry mass accumulation and allocation of 1-8 years old Q. variabilis seedlings, and path analysis was adopted to determine the key factors affecting the regeneration of the seedlings. In the distribution regions, the density of the seedlings decreased with their increasing age, and the density of the 1-8 years old seedlings all decreased in the order of south slope of Qin-ling Mountains > north slope of Qinling Mountains > Loess Plateau. The transformation rate of the seedlings with adjacent ages differed significantly among the three distribution regions. On Loess Plateau, the transformation rate of 7 years old to 8 years old seedlings was the lowest (30.2 +/- 2.9) %; on the north and south slopes of Qinling Mountains, the transformation rate of 4 years old to 5 years old seedlings was the lowest, being (53.9 +/- 3.7) % and (50.0 +/- 2.1) %, respectively. With the increasing age of the seedlings, their height and dry mass presented an increasing trend, with the order of south slope of Qinling Mountains > north slope of Qinling Mountains > Loess Plateau, the rate of root length to plant height tended to decline, and the rates of root breadth to canopy breadth and of root dry mass to shoot dry mass decreased after an initial increase. The rates of root length to plant height, root breadth to canopy breadth, and root dry mass to shoot dry mass were all the highest on Loess Plateau, and the lowest on south slope of Qinling Mountains. Air temperature, irradiance, canopy density and shrub coverage were the direct key factors affecting Q. variabilis seedling regeneration, among which, air temperature and irradiance were the positive factors, while canopy density and shrub coverage were the negative ones. Soil available nitrogen content and herb coverage were the indirect key factors affecting the Q. variabilis seedling regeneration positively and negatively, respectively.