Abstract
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.
Highlights
Increasing CO2 and other greenhouse gases (CH4 and N2O) will lead to an increase of 1.5 ̊C - 4.5 ̊C in the mean global surface temperature by 2100 [1] [2]
The objective of this study was to determine the effect of soil temperature and competition on the biomass allocation of Sargent spruce (Piceabrachytyla) and Purple cone spruce (P. purpurea), two dominant species in the subalpine coniferous forest in western Sichuan Province, China
When analyzing the single temperature effect in detail within seedling species there was an increasing trend in both aboveground and belowground biomass allocation at increased soil temperatures compared with the natural cold temperature, which is in accordance with the theoretical pattern and earlier findings [20] [48]-[51]
Summary
Increasing CO2 and other greenhouse gases (CH4 and N2O) will lead to an increase of 1.5 ̊C - 4.5 ̊C in the mean global surface temperature by 2100 [1] [2]. Soil temperature is one of the key determinants of abiotic and biotic processes in the understanding of complex ecosystem dynamics under changing climate conditions in arctic-alpine regions [8] [9]. At the alpine/subalpine treeline, cold soil temperatures are one of the major factors that can limit seedling growth, which directly or indirectly influence the availability and absorption of nutrient and water uptake [14]-[16], root growth and respiration [17] [18], physiological activities [19]-[21], and eventually source-sink dynamics between roots and shoots [22], biomass production [2], and even carbon sequestration in future forest ecosystems [23] [24]
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