云南腾冲上新统Platycladus tengchongensis sp.nov.表皮构造与古CO_2恢复

Cuticular microstructure of Platycladus tengchongensis sp.nov.from the Pliocene of Tengchong,Yunnan,and reconstruction of paleoatmospheric CO_2

在云南腾冲上新统芒棒组发现了角质层保存完好的侧柏化石。通过与已知化石种及最近亲缘种的宏观形态和微细构造特征对比,建立一新种Platycladus tengchongensis P.Deng et B.N.Sun sp.nov.。基于当前新种与现生种Platycladus orientalis和化石种Platycladus yunnanensis在宏观形态及角质层特征的相似性,统计了3个种的气孔密度和气孔指数,并用气孔比率法重建了云南腾冲上新世晚期和云南梁河晚中新世的古大气CO_2浓度分别为417.9×10^(-6)(386.5×10^(-6)~471.3×10^(-6))和409.9×10^(-6)(392.2×10^(-6)~433.3×10^(-6)),结果与Berner全球碳平衡模型中CO_2浓度变化曲线上的变化范围基本相符,故表明Platycladus tengchongensis和Platycladus yunnanensis叶片可以作为测量古大气CO_2浓度变化的生物指标。根据文中恢复的云南西部上新世晚期和晚中新世古大气CO_2浓度平均值均高于现在,推测新近纪时期云南西部的气候比现在温暖。综合云南腾冲地区已有的古气候研究与化石和现生叶片角质层特征的对比分析,认为云南腾冲上新世晚期气候较为温暖湿润。此外,文中化石的发现为侧柏属自然分布的研究提供了宝贵的材料。

A fossil identified as Platycladus was collected from the late Pliocene sediments of the Mangbang Formation from Tengchong County,Yunnan Province,China,which was well preserved with cuticular substance.On the basis of the comparison with fossil species and relevant extant relative species of the Platycladus in gross morphology and anatomy features,we identified it as a new species,Platycladus tengchongensis sp.nov.As both the present fossil specimens and Platycladus yunnanensis had similar gross morphology and epidermic features with Platycladus orientalis,the stomata density and stomata index of three kinds of Platycladus were calculated.The paleoatmospheric CO_2 concentration were estimated based on stomatal ratio approach in the late Pliocene of Tengchong and the late Miocene of Lianghe,and the estimated values were417.9×10^-6（386.5×10^-6-471.3×10^-6）and 409.9×10^-6（392.2×10^-6-433.3×10^-6）,respectively.The result was consistent with the CO_2 curve of Berner＇s global carbon balance model（GEOCARBⅢ）,which indicates that the leaf of Platycladusteng chongensis and Platycladus yunnanensis are good biological indicators for reconstructing the paleo-CO_2.The mean atmospheric CO_2 concentration in the late Miocene and the late Pliocene of western Yunnan were higher than present days,and therefore it can be inferred that the climate was warmer in the Neogene of western Yunnan than present days.Based on the existing climate research and the comparison of cuticular characteristics between the fossil and the modern leaves,it can be inferred that the climate was warmer and humid in the late Pliocene of western Yunnan than in the present.In addition,the occurrence of present fossil provides precious materials for the study of natural distribution of Platycladus.