青藏高原东南缘陇蜀杜鹃当年生小枝茎叶性状对海拔变化的响应

Responses of stem and leaf traits of Rhododendron przewalskii to altitude in the southeastern Qinghai-Tibet Plateau

通过在青藏高原东南缘的岷江源区三处高山林草交错带采集陇蜀杜鹃当年生小枝,测量小枝的茎长、茎粗与茎生物量,沿海拔梯度自然分布的空间变化对比其当年生小枝的茎结构与生物量及其相互关系,接着比较了总叶质量和比叶面积的变化,最后通过典范对应分析(CCA)探究小枝茎叶性状与土壤因子的相关关系,有助于理解陇蜀杜鹃适应异质环境的生态适应对策。结果表明:(1)除弓杠岭外,斗鸡台与卡卡山土壤因子在海拔间差异显著,相似海拔不同山地间土壤因子也存在显著差异。(2)除卡卡山高海拔比叶面积显著小于低海拔外,其他样地的小枝茎性状(茎长、茎粗、比茎长和茎生物量)和叶性状(总叶质量和比叶面积)在海拔间并无显著差异,相似海拔不同坡体间茎粗、茎生物量以及比茎长差异也未达到显著水平(P>0.05),但弓杠岭(3963 m)的茎长显著大于卡卡山(3921 m)(P<0.05)。(3)小枝茎长、茎粗与茎生物量之间均为异速生长关系,且茎生物量累积速率大于茎长和茎粗增加的速率,且茎长的增加速率约为茎粗的2.8倍。(4)CCA排序结果表明,11个土壤环境因子中,碳含量、碳氮比、有机碳含量、总磷和容重对植物性状有显著的影响,但在海拔及不同山体间影响小枝茎叶性状的土壤因子不同。由此可知,较小的海拔梯度变化对小枝茎叶性状影响较小,土壤因子是导致小枝茎叶性状差异的重要原因之一。

The current year twigs of Rhododendron przewalskii were collected across three forest-grassland ecotones in the headwater region of Minjiang River in the southeastern Qinghai-Tibet Plateau. Along altitudinal gradients of their natural spatial distribution, stem length, stem thickness, and stem biomass of the twigs, as well as their relationships were measured and compared. Then, we compared total leaf mass and specific leaf area. Lastly, the relationships between stem and leaf traits and soil factors were evaluated by canonical correspondence analysis(CCA). The results show that except for Gonggangling, the soil factors of Doujitai and Kaka Mountains differed significantly between altitudes, and there were also significant differences in soil factors between different mountains at similar altitudes. Except that the high altitude specific leaf area of Kaka Mountain is significantly smaller than that of low altitude. Neither traits of stem(stem length, stem thickness, specific stem length and stem biomass) have no significant differences between altitudinal sites. Stem thickness, stem biomass, and specific stem length from similar altitudes also show no significant differences across sampling sites(P> 0.05). However, the stem length at Gonggangling(3963 m) is significantly greater than that at Kaka Mountain(3921 m)(P<0.05). The relationships between stem length, stem thickness and stem biomass exhibit allometric growth, while stem length has an invariant allometric scaling relationship with stem thickness(SMA slope 2.8). The CCA results show that, carbon content, carbon to nitrogen ratio(C/N), soil organic carbon(SOC), total phosphorus(TP) and soil bulk density(SBD) were the main factors affecting stem and leaf traits. In general, small changes between different altitude gradients have little effect on stem and leaf traits of twigs, and soil environmental factors can be important reasons triggering the differences of the stem and leaf trait.