The Growth of Two Species of Subalpine Co-nifer Saplings in Response to Soil Warming and Inter-Competition in Mt. Gongga on the South-Eastern Fringe of the Qinghai-Tibetan Plateau, China

摘要

In conjunction with global climate change, soil temperatures have been recorded to be increasing more rapidly than air temperatures at Mt. Gongga, China. Plant density is also increasing, and a means of combining the effects of changes in soil temperature and competition on the growth and regeneration of the constructive coniferous species seedlings in the subalpine ecotones is needed. Thus, a split-plot design experiment was conducted with Sargent spruce (Picea brachytyla) and Purple cone spruce (P. purpurea) saplings, using four soil temperatures (control Tsoil = 11.9℃ ± 0.3℃, low Tsoil = 13.4℃ ± 0.140℃, intermediate?Tsoil = 15.4℃ ± 0.1℃, high Tsoil = 16.4℃ ± 0.2℃) and three plant densities (one, two and three saplings per pot), in the subalpine ecotone. Soil temperatures were controlled through a cable heating system. After two growing seasons under the soil temperature treatments, 107 Sargent spruce saplings and 110 of the same-aged Purple cone spruce saplings were harvested. The results showed that Sargent spruce grew faster and with a greater biomass productivity than Purple cone spruce. Increased soil temperature significantly increased leaf biomass, branch biomass, above-ground biomass, and total plant biomass for developing crown architecture in Sargent spruce, whereas plant competition (i.e., higher density) notably caused a decline in leaf biomass, branch biomass, and above-ground biomass. Purple cone spruce did not respond to either an increases in soil temperature or plant competition. Neither plant species was influenced by the interaction of soil temperature and plant competition. These results suggest that Sargent spruce may expand the upper and lower limits of its distribution as global warming continues, but the expansion is likely to be restricted by plant competition in the future, including that from Purple cone spruce. Below-ground, fine root biomass does not change with soil warming although other sized roots do in both species. This signifies that light availability is more important in the acclimation of Sargent spruce to the changing environments than soil nutrient availability. Purple cone spruce is unaffected by the complex changing environment, suggesting that this spruce may stably grow and continue to thrive in the subalpine ecotone in future scenarios of climate change.