碳氮稳定同位素指示苔藓生境特征以及树冠对大气氮沉降的吸收  

δ^(13)C and δ^(15)N of moss (Haplocladium microphyllum (Hedw.) Broth) for indicating habitats difference and canopy retention on atmospheric nitrogen deposition

作　　者：刘学炎[1,2] 肖化云[1] 刘丛强[1] 李友谊[1,2] 

机构地区：[1]中国科学院地球化学研究所环境地球化学国家重点实验室 [2]中国科学院研究生院,北京100049

出　　处：《地球化学》2007年第3期286-294,共9页Geochimica

基　　金：中国科学院知识创新工程重要方向项目(KZCX3-SW-140);国家自然科学基金(40573006)

摘　　要：对贵阳地区一生境内不同生长条件(石生苔藓、无树冠、不同树冠类型以及同种树冠不同树冠厚度)下的细叶小羽藓(Haplocladium microphyllum(Hedw.)Broth)碳氮同位素进行了研究。不同生境的苔藓δ13C和δ15N值具有相似的变化趋势和明显的相关关系。石生苔藓δ13C和δ15N值比土生苔藓偏高指示了其相对干燥和受到干沉降控制的生境;树冠下方光照条件差、湿度高、缺少干沉降氮的输入是苔藓δ13C和δ15N值偏低的主要原因;而树冠类型、叶片形态、叶面性质造成树冠对大气沉降氮吸收能力的不同是三种树冠下方苔藓氮同位素组成差异的潜在因素。此外,同一树冠(桂花树Osmanthus fragrans Lour.)下方苔藓的氮含量和碳氮同位素平均组成与树冠厚度呈线性关系,尤其是δ15N的响应很好地反映了吸收过程中树冠厚度对大气沉降氮源同位素组成的控制作用。结果表明,苔藓δ13C值能很好地指示苔藓的生境差异和生理响应(如光合作用能力和氮需求等);而δ15N值在示踪氮源和反映不同树冠吸收过程的同位素分馏效应方面更具有优势,二者的相关关系是环境因素相互作用的重要线索。此外,细叶小羽藓Haplocladium microphyllum(Hedw.)Broth具有高效利用大气沉降氮和分布广泛等特点,可进一步应用于该地区大气氮沉降的指示或监测研究。A unique survey of biologically important stable isotope pairs （δ^13C and δ^15N） of pleurocarpous moss Haplocladium microphyllum （Hedw.） Broth in Guiyang was undertaken. Samples collected in a niche according to different habitats （epilithic mosses, mosses without upper canopy, mosses under different canopy and different canopy thickness） were analyzed for comparing habitats difference and determining canopy retention mechanisms on atmospheric nitrogen deposition. Similar variations and significant correlation between meanδ^13C and δ^5N signatures were seen in mosses from different habitats. These signals indicate that desiccation and dry deposition input were the main causes of high δ^13C and δ^5N values, while low light intensity, high humidity and lack access to dry deposition were attributed to more negative values of mosses under canopies, and defoliation or not, leaf morphology and surface wettability may be responsible for difference between canopy types. Moreover, moss nitrogen content and isotopic ratios show different linear relationship with canopy thickness, especially for δ^15N, in which the δ^15N discrimination by this single factor was well identified. Consequently, moss δ^13C may be a good marker for habitats or environmental and physiological factors （e. g. photosynthesis and N demand）, while moss δ^15N was undoubtedly a better tracer of atmospheric processes. The strong correlation between δ^13C and δ^15N nitrogen sources and fractionation in canopy retention of mosses may be an integrator of interaction between each environmental factor. Finally, Haplocladium microphyllum （Hedw.） Broth can be further taken as indicator or monitor of atmospheric nitrogen deposition for its efficient uptake of atmospheric-derived N and widespread habitats.

关 键 词：Δ^13C δ^15N 大气氮沉降 苔藓 树冠 吸收 

分 类 号：P597[天文地球—地球化学] P593[天文地球—地质学]