卧龙亚高山暗针叶林不同林冠环境下华西箭竹分株种群结构特征

The ramet population structures of the clonal bamboo Fargesia nitida in different canopy conditions of sulbalpine dark coniferous forest in Wolong Nature Reserve,China

详细调查了林下、中林窗、大林窗和林缘旷地等4种亚高山暗针叶林林冠环境下的华西箭竹(Fargesia nitida)分株种群,对其表现结构(株高、基径和生物量)和年龄结构进行了较系统的对比研究。主要研究结果如下:(1)分株水平上,华西箭竹表现结构在4种林冠环境下均有极显著差异(p<0.01),且随林冠郁闭度的减小,分株个体的高度、基径和生物量有递增的趋势(林下<中林窗<大林窗);(2)分株各构件在总生物量中所占比例随林冠环境变化而改变:除林缘旷地外,叶的生物量百分比与林冠郁闭度呈正相关。林缘旷地中,地下茎和根系的生物量百分比均高于其余3种环境;(3)不同林冠环境下分株单位叶面积叶重存在显著差异(p<0.05),且随林冠郁闭度的减小而增大。单叶生物量和单叶面积均以中林窗最大,林缘旷地次之,二者与大林窗或林下均有显著差异(p<0.05)。华西箭竹的单株叶片数量以大林窗最大,与其余3种环境有极显著差异(p<0.01);(4)分株种群的死亡率以林下最低(p<0.01),但各种群平均年龄间无显著差异(p>0.05)。可见,华西箭竹分株种群对林冠环境变化的反应主要体现在形态和生物量分配上,而非种群的年龄上。

The bamboo Fargesia nitida, one of the Giant Panda＇s main food sources and dominant shrub species of the forest understory, is mainly distributed in the dark coniferous belt （at altitudes of 2450m to 3200m） in western Sichuan and southern Gansu in China. To study the impacts of different forest canopy conditions on subalpine dwarf bamboo populations, ramet population structures of clonal Fargesia nitida were surveyed in： forest understory（FU）, moderate gap（MG）, large gap（LG） and forest edge wilderness（FEW）. In order to reveal whether these four canopy conditions affect the ramet structures and to estimate the effect sizes, a field census of Fargesia nitida populations＇ age structure, morphological traits（culm height, basal diameter and leaf area） and biomass allocation was conducted in an Abies faxoniana forest situated in Wolong Nature Reserve in western Sichuan, China. The main results showed that ： （ 1 ） At the ramet level, the performance structures of the four populations were significantly different（one-way ANOVA, p 〈 0.01 ）, and as the canopy cover decreased the mean height, basal diameter and biomass of the populations increased in the order of FU 〈 MG 〈 LG; （2） The modular biomass proportions of ramets varied with different canopy conditions and leaf biomass proportion was positively related to canopy cover except for FEW, in which the biomass proportions of rhizome and roots were both higher than those in the other three canopy environments; （3） The ramet specific leaf mass increased in parallel with the decrease of canopy cover （one-way ANOVA, p 〈 0.05） of the four different populations. In the MG, the individual leaf biomass was the heaviest and individual leaf area the largest, followed by those in the FEW. Both the individual leaf biomass and leaf area were respectively different from those in the FU or LG（one-way ANOVA, p 〈 0.05 ）. Leaf number per ramet in the LG was the biggest and was significantly different among the four different canopy conditions（one-way ANOVA, p 〈 0.01） ; （4） The ramet population mortality was the lowest in the FU （Chi-square test, p 〈 0. 01）, while there was no significant difference in the average population age （Mann-Whitney test, p 〉 0.05）. All the results indicated that it was not ramet age, but the morphological changes and biomass distribution that exhibited the response of the ramet population of Fargesia nitida to changed canopy conditions.