贡嘎山现代植物叶蜡脂肪酸氢同位素组成及对海拔变化的响应

文章探讨了贡嘎山东坡不同海拔高度植物和土壤饱和脂肪酸的δDwax值,结果显示,土壤δDwax值与海拔显著负相关(R2=0.71),与前人报道的贡嘎山东坡土壤水、土壤正构烷烃δD值与海拔间的关系存在相同的趋势。植物δDwax值与海拔间的关系与土壤水及土壤相似,但相关性不明显(R2=0.11),然而,研究结果显示木本植物和草本植物的δDwax值随海拔变化存在明显的差异,总体上草本植物的氢同位素要更负。贡嘎山木本植物、草本植物和土壤的εwax-sw值随海拔的变化波动较小,但木本植物的加权平均δDwax值和εwax-sw值(土壤水和叶蜡之间的氢同位素分馏系数)比草本植物大约偏正38‰和43‰,表明它们各自对随海拔高度降水同位素变化有不同的响应。也即,沿海拔植物δDwax值同时受降水δD值和植物类型两个因素控制。因此,结果揭示土壤δDwax值随海拔的变化与木本植物和草本植物存在相同的趋势,木本植物的δD值比草本植物大约偏正了38‰,这个趋势显示植物类型的变化将不可避免的影响土壤饱和脂肪酸δDwax值与海拔间的关系。由于植物类型随海拔增加会有较大的变化,建议利用饱和脂肪酸δDwax值重建古海拔前需要对植物类型进行评估。

HYDROGEN ISOTOPIC VARIATIONS OF LEAF WAX n-FATTY ACIDS IN MODERN PLANTS AND THE RESPONDING TO ALTITUDE ON MOUNT GONGGA

In this study we present leaf wax n-fatty acids hydrogen isotope data from different life form plants and surface soils(including 15 grasses,24 woody plants and 11 soil samples)along the eastern slope of Mount Gongga over a range from 1200m to 3600m above sea level.Mount Gongga,located on the eastern side of the Tibetan Plateau in Sichuan Province(29°20'~30°00'N,101°30 '~102°10'E; peak at 7556m above sea level,a.s.l),is the highest part of Daxueshan.The hydrogen isotope ratios (δDwax) of the C24,C26,C28,and C30 n-fatty acids range from -250 ‰ to -109 ‰ ,and are strongly inter-correlated(R2=0.87 for C26 and C24,R2=0.78 for C26 and C28,and R2=0.74 for C26 and C30; pδDwax values for soils with altitude(δDwax=-2.23h-128.7,R2=0.71),the same correlation as δDsw values of soil water and δDwax values of soil n-alkane with altitude in previous study.The δDwax values of plants show a similar trend with altitude as those for soil and soil water,but with a weak linear correlation(R2=0.11).Notably,our data identify significant differences in δDwax values between woody plants and grasses,with the grasses showing more negative δDwax values.The εwax-sw values(hydrogen isotope fractionation between plants and soil water)show minor fluctuation with altitude.However,the δDwax and εwax-sw values of woody plants,are roughly 38 ‰ and 43 ‰ more positive than those of grasses respectively,suggesting that an "altitude effect" could also be documented in the δDwax of woody plants and grasses,with each responding independently to changes in precipitation along the altitude transect.In other words,the δDwax values of plants along the altitude transect are simultaneously controlled by two factors,δD value of precipitation and plant type.The δDwax values for soils show a similar trend with altitude as those observed for woody plants and grasses,but the δDwax values for grass are ca.38 ‰ more negative than those for woody plants.This trend suggests that a change in plant life form will inevitably change the relationship between the δDwax values of soil n-fatty acids and altitude.Because plant life form is widely known to vary with altitude,our results suggest that a preliminary evaluation of plant life form is necessary when reconstructing the paleoelevation using the δDwax values of soil n-fatty acids.