色季拉山急尖长苞冷杉叶片及细根性状随海拔的变异特征

叶片和细根是植物对环境变化响应的主要功能器官,在气候变化趋势下,研究其随环境梯度的变化,对理解植物对环境的适应策略具有重要意义。本文是在色季拉山急尖长苞冷杉分布区,按海拔梯度(3800、3900、4000、4100、4200、4300、4400m)选择7个典型样地,在样地内对其叶片基本特征、叶绿素含量、比叶重和细根特征(0—60cm)等参数进行了测量。结果表明:(1)随海拔梯度升高,急尖长苞冷杉叶片叶面积减小、叶片厚度增加、叶绿素含量逐渐降低、比叶重显著增大。3900m处急尖长苞冷杉的叶片形态特征表现最好,叶片长度、宽度和面积均显著优于其他海拔,海拔4200m叶片厚度达到最大值,叶片面积、叶绿素含量随海拔升高呈下降趋势,但在4200m处出现第二峰值。(2)随海拔梯度增加,细根各性状与海拔表现出非线性关系,其中细根生物量和细根体积在3900m和4200m处出现两次峰值,3900m处细根生物量达到最大值,4200m处细根体积达到最大值,4400m处细根生物量和细根体积均显著少于其他海拔。细根根长密度在海拔3900、4200、4300m较高,三者之间差异不显著,但显著高于其余海拔,4400m海拔细根根长密度最小。细根表面积在3900m海拔处达到最大值,显著高于其他海拔,4200和4300m次之,3800、4000和4400m海拔下细根表面积相对较小。4400m处细根比根长达到最大值。各海拔上细根均主要分布在0—20cm土层。随土层厚度增加,各海拔细根生物量和根系体积在0—60cm土层范围内均逐渐减小;细根根长密度、表面积在20—40cm和40—60cm显著提高;同一海拔细根比根长随土层深度增加呈明显的增加趋势。各海拔40—60cm土层细根比根长显著高于20—40和0—20cm土层。(3)综合叶片及细根特征,海拔3900m为急尖长苞冷杉的最适宜生长区域;随海拔升高,环境因子逐渐恶劣,环境胁迫加剧,急尖长苞冷杉最终形成在4400m处为其分布上限的海拔梯度格局。

Variation in leaf and fine root traits with altitude in Abies georgei var. smithii in Mt. Shergyla

The relationship between plant and environment is one of key issues in the field of ecology. Plant functional traits and the responses of some traits to environment have been of interest to scholars since the 19th century. Studies on the changes in plant leaf and fine root traits and their correlation with elevation gradient explain how plants respond and adapt to a changing environment. Leaf length, width, thickness, area, specific leaf weight, chlorophyll content, root activity, fine roots (at a soil depth of 0-60 cm) characteristics, and other parameters of Abies georgei var. smithii at seven sites located at different elevations (3800, 3900, 4000, 4100, 4200, 4300, 4400 m) on Mt. Shergyla were measured and analyzed to understand the variation in leaf and root morphology along the elevation gradient and elucidate the response mechanism in plants growing at timberline in Southeastern Tibet. The results showed that: (1) Leaf thickness increased and leaf area, chlorophyll content, and root activity decreased with the increase in elevation. The optimal growth of A. georgei var. smithii was observed at the elevation of 3900 m. The leaf length, leaf width, and leaf area were significantly better than the other elevations. The greatest blade thickness was observed at 4200 m elevation. Leaf area and chlorophyll content decreased with elevation, but appear at the second peak at 4200 m.(2) Fine root biomass and fine root volume were the greatest for individuals growing at 3900 m and 4200 m, respectively. However, the two parameters were significantly lower in trees growing at 4400 m compared to the trees growing at other elevations. The fine root length density was relatively high at 3900, 4200, and 4300 m elevation; there was no significant difference in this parameter between trees growing at these three elevations, but the measured values were significantly higher compared to those calculated for trees at other elevations. The fine root length density was minimal for trees growing at 4400 m. The fine root surface area was significantly higher for trees growing at 3900 m compared to other elevations, followed by that observed in trees at 4200 m and 4300 m elevation. The fine root surface area was relatively small for trees growing at 3800, 4000, and 4400 m elevation. Specific root length reached the maximum at 4400 m. Root biomass and volume of A. georgei var. smithii measured at a soil depth of 0-60 cm and fine roots biomass and volume at a soil depth of 0-20 cm gradually decreased with the increase in soil thickness at each altitude. The fine root biomass and root volume were the highest for trees growing at 3900 m and 4200 m elevation. The root length density and root surface area had a significant increase at soil depths of 20-40 cm and 40-60 cm. As the soil depth increased, fine specific root length also increased, reaching the maximum at a soil depth of 40-60 cm. (3) Considering the characteristics of leaves and fine roots, the altitude of 3900 m is the optimal elevation for growth of A. georgei var. smithii. Timberline is located at 4200 m elevation, which indicates the zone of harsh environmental conditions and where Abies georgei var. smithii reaches its upper limit of distribution at the elevation of 4400 m in this region.