Influence of topography, soil properties and plant community on the biomass of Abies georgei var. smithii seedlings in Southeast Tibet

Biomass of seedlings at different developing stages of growth is important information for studying the response of species to site conditions.The objectives of this study was to explore the distribution characteristics of AGB(above-ground biomass) and BGB(below-ground biomass) of Abies georgei var. smithii seedlings of different ages, and investigate the effects of topography(slope aspect,altitude),plant community characteristics(crown density, species diversity, etc.), and soil properties(soil physical and chemical properties) on the biomass and its allocation. Seedlings in five age classes(1–2, 3–4, 5–6, 7–8, and 9–10 years old) were collected by full excavation from 6 elevations(3800 m,3900 m, 4000 m, 4100 m, 4200 m, 4300 m) on the north and south slopes of Sejila Mountain in Tibet. 15seedlings of each age class were investigated at one altitude. The individual effects of seedling age(SA)and the interaction effects of SA, slope aspect(SL),and elevation(EG), namely, SL×EG, SL×SA, EG×SA,and SL×EG×SA, had significant effects on the AGB of the seedlings(p<0.05), whereas BGB was only significantly affected by SA(p<0.001). The AGB and BGB of the seedlings showed a binomial growth trend with the increase in seedling age, and had an allometric relationship at different elevations, α(allometric exponential) varied from 0.913 to 1.046 in the northern slope, and from 1.004 to 1.268 in the southern slope. The biomass of seedlings on the northern slope was remarkably affected by stand factors, with a contribution rate of 47.8%, whereas that on the southern slope was considerably affected by soil factors with a contribution rate of 53.2%. The results showed that age was the most important factor affecting seedling biomass. The allometric pattern of seedling biomass was relatively stable, but in a highaltitude habitat, A. georgei var. smithii seedlings increased the input of BGB. Understanding seedling biomass allocation and its influencing factors is useful for evaluating plants’ ability to acquire resources and survival strategies for adaptation to the environment in Tibet Plateau.