Global warming as a result of greenhouse gas emissions is predicted to increase air temperature during this century. Forests are important terrestrial ecosystems, and are particularly sensitive to climate change. Increasing temperatures could have a number of serious consequences for forests such as prolonging the growth season of plants; changing the structure and dynamics of plant communities; changing the geographic distribution of communities (extending into the alpine region); blocking photosynthesis, and affecting biodiversity. These impacts, in turn, can be expected to have consequences for the structure and function of forest ecosystems, especially in high latitude and altitude regions. Gongga Mountain is in the subalpine zone of the eastern area of Qing-Tibet Plateau, and is thought to be a fragile zone sensitive to climate change. The terrestrial ecosystems in this region are predicted to experience climate change.
Abies fabiri(Mast.) Craib is one of the dominant conifers in the subalpine area of the western Sichuan Province of China. This species is very important for the ecosystem in this region as the main constructive species of the subalpine dark coniferous forests. Temperature and N nutrient supply have been recognized as the two limiting growth factors of Abies fabiri. The present study investigated the effects of a short-term warming on growth, nutrients and stoichiometric traits of Abies fabiri seedlings. We artificially simulated global warming using an infrared heater at the nearby Gongga Alpine Forest Ecosystem Observation Station, Chinese Academy of Sciences. In the growing season, the average monthly temperatures of soil at depths of 5, 10 and 20 cm were increased by 5.04℃, 4.81℃ and 4.35℃, respectively, air temperature was increased 1.12℃ also; however, soil water content at depths of 5, 10 and 20 cm were decreased by 7.03%, 6.10% and 6.40%, respectively, and air relative humidity was decreased by 6.30% as well. Total biomass was decreased by short-term warming compared with the biomass of the control seedlings. Root length, basal diameter, plant height, root shoot ratio, leaf mass ratio, root mass ratio and specific leaf area (SLA) also decreased, while stem mass ratio increased with short-term warming. These findings indicated that seedling growth was impeded by short-term warming. Additional data showed that C concentrations in stems and leaves were decreased by 7.75% and 2.29%, while concentrations increased by 2.76% in roots. However, there were no significant effects of short-term warming on C concentrations in root, stems or leaves (P > 0.05). N concentration in stems was significantly decreased by 14.49% (P < 0.05) while concentrations in roots and leaves increased by 19.78% and 5.70% but these were not significant (P > 0.05). There were no effects of short-term warming on the P concentration in roots, stems or leaves compared with the control seedlings. Short-term warming also affected the stoichiometric characteristics of Abies fabric in root, stem and leaves but these differences were not significant. The ratios of C ∶ N and N ∶ P in seedlings exposed to short-term warming were lower than in the control seedlings. In contrast, the C ∶ P ratio was higher than in the controls. The order of mean ratios were: stem (92.59±4.92)> root (61.89±1.65)>leaf (60.81±3.23) for C ∶ N ratios, leaf (4.99±0.22)> root (4.44±0.58)>stem (3.64±0.10) for N ∶ P ratios, and stem (336.35±8.70)>leaf (302.85 ± 4.49)>root (274.86±5.27) for C ∶ P ratios. In summary, this study suggests that short-term warming decreased seedling growth, altered biomass allocation and C ∶ N ∶ P stoichiometry pattern. A shortage in N nutrient supply is suggested to have caused the decreased growth of seedlings in the warming and control treatments.