7556 m high Gongga Mountain is located in the eastern margin of Qinghai-Tibet Plateau (29°34'40.89"N, 101°55'23.91"E) of China. The high regime is more sensitive to global change, and mean annual air temperature has increased by 0.57°C compared to 0.32°C in the lowlands of China since 1990. Recent 22-year meteorological data at 3000-m elevational Forest Ecology Research Station at Institute of Mountain Hazards and Environment, Chinese Academy of Sciences, indicates soil warming is rapider than air warming in the mountain. The increase is 1.5°C for soil at 10-cm depth, and 0.6°C for air. Additionally, global change likely increases plant density in the forests. Sargent spruce (Picea brachytyla) is an endangered tree species, and grows with koyama spruce (Picea koraiensis ) from 1400- to 2000-m altitudes in the mountain. How growth responses of both species saplings to the changing environments have never been known. Thus, an experiment of split-plot design was conducted with 6-year old saplings of both species, four soil temperatures (low =13.43 ± 0.14ºC, middle = 15.45 ± 0.14ºC, high = 16.42 ± 0.15ºC, natural temperature = 11.90 ± 0.25ºC) and three plant competitions (1, 2 and 3 saplings of the same species per pot) with 6 replications at the station from April 28 to August 14, 2009. The temperatures were controlled by heating cable control systems.

Results/Conclusions

107 sargent spruce and 110 koyama spruce saplings were harvested to measure basal diameter, height, biomass of leaves, branches, stem, fine roots, coarse fine roots and coarse roots. Total plant biomass, total root biomass, aboveground biomass and root/shoot ratio were calculated. The results showed sargent spruce grew faster, and had higher biomass productivity than that in koyama spruce. Biomass of sargent spruce increased more in soil warming and more sensitive to plant competition than that of koyama spruce, implying understory sargent spruce would better grow as global warming continues, but the growth is restricted by increasing plant density in the future. Aboveground, soil warming increased leaf and branch biomass for developing crown architecture in sargent spruce, but did not in koyama spruce. Belowground, fine root biomass did not change with soil warming except for the other sized roots in both species. That signify light availability is more important in the acclimation of sargent spruce to the changing environments than soil nutrient availability. Koyama spruce is insensitive to the changes, and would grow stably in the ecoton in the future.