色季拉山林线不同生活型植物稳定碳同位素组成特征

Characteristics of stable carbon isotope compositions of different life form species growing at the timberline in Sergyemla Mountain

通过测定青藏高原东南部色季拉山林线处典型冷湿气候条件下植物叶片δ13C值,从物种、生活型(常绿乔木、常绿灌木、落叶灌木及草本)两个水平研究该地区植物的水分利用策略是否存在明显的分异,进一步验证生活型能否用来划分林线地区极端环境条件下生理学特征(碳-水平衡)类似的不同植物类群。结果表明,所测定的隶属于18科、28属的31种植物叶片的δ13C值介于-30.24‰和-25.39‰之间,平均值为-27.68‰,表明色季拉山研究区内植物的碳固定均通过C3光合作用途径实现,没在C4植物的分布。常绿灌木黄杯杜鹃与海绵杜鹃δ13C值无显著性差异(P>0.05),落叶灌木西南桦楸、山生柳以及冰川茶藨子也无显著性差异(P>0.05)。相反,不同生活型植物之间叶δ13C值差异显著(P<0.01),为常绿乔木(冷杉)(-27.27‰)>常绿灌木(-27.56‰)>落叶灌木(-27.93‰)=草本(-27.91‰)。本研究结果表明在色齐拉山高山林线地带,尽管水分相对充足,但不同生活型植被之间存在明显不同的稳定碳同位素分馏。同一生活型的叶δ13C值无显著差异,而不同生活型植物δ13C值差异显著,说明植物水分利用策略的变化主要是由于生活型的变化引起的,即不同生活型植物的叶δ13C值可综合反映不同功能类群植物的水分利用策略变化。

Water availability is not generally considered the most limiting resource at high elevations,especially at timberline area due to the higher soil water content and more abundant precipitation,which may result in no difference in leaf δ13C among plants.Variations in leaf δ13C in conifer,evergreen and deciduous shrubs and forbs were studied at the timberline in Sergyemla mountain,on the south-eastern edge of the Tibetan Plateau.We aimed at investigating the water use strategy at both plant species and life-form（tree,shrub or forb）levels to determine if life form could be used to group plants with similar physiological characteristics,e.g.the balance between CO2 and water fluxes under extremely environmental conditions.The results suggested that the δ13C values of 31 species belonging to 18 families and 28 genera ranged from-30.24‰ to-25.39‰,with a mean of-27.68‰,showing that all species perform photosynthesis through the C3 pathway.At the species level,no significant differences in δ13C values were found in evergreen shrubs（Rhododendron wardii,R.pingianum）or deciduous shrubs（Sorbus rehderiana,Salix oritrepha and Ribes glaciale）（P〉0.05）.However,life form-specific difference in δ13C values was highly significant（P 〈 0.001）,with the sequence of evergreen trees（-27.27‰）〉 evergreen shrubs（-27.56‰）〉 deciduous shrubs（-27.93‰）and forbs（-27.91‰）.The results indicated that although soil water availability is high at the timberline,significant differences in isotope fractionation occur in individuals,suggesting different water use efficiency（WUE）.There is no difference in δ13C in plants with the same life forms but a significant difference between different life forms,suggesting that the variation of WUE is dependent on life form.The δ13C values of different life forms could be an integrated indicator of changes in water use strategy among functional groups at the timberline.