短期增温对贡嘎山峨眉冷杉幼苗生长及其CNP化学计量学特征的影响

2009年5月至10月，在中国科学院贡嘎山高山森林生态系统观测站附近，采用红外灯加热人工模拟气候变暖研究了增温对峨眉冷杉(Abies fabiri (Mast) Craib)幼苗生长和养分及其化学计量特征的影响。由于红外灯的增温作用，在幼苗的整个生长季节，增温样地地表下5 cm、10 cm、20 cm处土温平均高于对照样地5.04 ℃、4.81 ℃、4.35 ℃，而土壤含水量则分别降低了7.03%、6.10%、6.40%；地表20 cm处空气温度相比对照样地上升了1.12 ℃，而空气相对湿度则降低了6.30%。除茎重比外，增温处理降低了峨眉冷杉幼苗的根长、基径、株高、总生物量、根重比、叶重比、根冠比和比叶面积。经方差分析发现，增温处理后幼苗根、茎和叶的C平均含量与对照差异性均不显著(P>0.05)，其中除茎的提高了2.76%外，根和叶分别降低了7.15%和2.29%；N平均含量除茎显著降低之外(P<0.05)，根、叶分别提高了9.78%和5.70%；幼苗根、茎、叶的P平均含量均低于对照11.97%、10.69%和2.99%，并且根和茎与对照存在显著性差异(P<0.05)。增温处理后幼苗根、茎、叶各器官的C︰N、C︰P 、N︰P与对照均不存在显著性差异(P>0.05)，其中C︰P均大于对照，而C︰N和N︰P与对照相比，均有不同程度的减小；C︰N、N︰P和C︰P的平均值(标准差)大小顺序依次为茎(92.594.92)>根(61.891.65)>叶(60.813.23)、叶(4.990.22)>根(4.440.58)>茎(3.640.10)和茎(336.358.70)>叶(302.854.49)>根(274.865.27)。实验结果表明：增温对幼苗生长和生物量积累具有明显的限制作用，对叶片生长的阻碍作用尤为突出；增温改变了幼苗根茎叶的CNP含量及其化学计量比格局；在养分供应上，增温和对照处理下幼苗生长均受N素限制。

Short-term effects of warming on growth and stoichiometrical characteristics of Abies fabiri (Mast.) Craib seedling in Gongga mountain

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 5.04C, 4.81C and 4.35C, respectively, air temperature was increased 1.12C 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.