热带山地表土植硅体组合对植被的指示--以马来西亚Jerai山为例

VEGETATION INDICATION OF PHYTOLITH ASSEMBLAGES OF TOPSOIL ON TROPICAL MOUNTAINS:A CASE FROM JERAI HILL,MALAYSIA

热带雨林植物花粉较低的表现力阻碍了东南亚地区冰期时古植被的精确重建。本研究分析了热带地区马来西亚Jerai山的14个不同海拔高度的表土植硅体样品,目的是评估植硅体是否可以作为古植被重建的关键指标。我们发现了17个植硅体形态类型,它们包括鞍型、棒型、多裂梯型、木本不规则形态、矩形、板型、维管组织、方型、块状、塔型、双裂片型、十字型、硅化气孔、球型、椭球型、楔型、楔型泡状细胞等。球型占据绝对优势的植硅体组合区别于热带稀树草原和亚热带常绿阔叶林等植被类型的植硅体组合,很好地指示了热带森林植被。禾本科植硅体较为敏感地指示了其母本植物的零星存在。随着海拔的升高,某些类型的百分比发生略微的变化,如低地龙脑香林带为球型-木本不规则形态-块状组合;丘陵龙脑香林带为球型-塔型-木本不规则形态组合;石楠林带和山地林带为球型-块状-木本不规则形态组合。这些结果显示了东南亚热带森林中的表土植硅体组合具有一定的植被指示意义。

This study analyzed 14 topsoil phytolith samples collected from 200 m to 1000 m a.s.l.on Jerai Hill of tropical Malaysia to evaluate the potential of phytolith assemblages as proxies for implying various paleovegetation types.Jerai Hill is located in Kedah State(5°44'~5°50'N,100°22'~100°29'E)of Peninsular Malaysia.The summit of the highest mountain is at 5°47'N,101°26'E,and the maximum elevation reaches to 1217 m.In this area,the typical vegetation type is the rainforest rich in Dipterocarpaceae species.With the increase in elevation,plant communities evidently change,particularly the richness of dipterocarp species which starts to decrease sharply above 400~500 m a.s.l.,upland species frequently occur above 900 m a.s.l.,and they are mainly composed of Myrtaceae,Fagaceae,and Dacrydium species.Phytoliths were extracted from the residues using the heavy liquid extraction technique.The heavy liquid was composed of Zn grains,potassium iodide,and hydroiodic acid,and specific gravity was set to 2.385.In each sample,at least 500 phytolith grains were counted.The results showed that there were a large number of phytoliths with various morphotypes in the 14 topsoil samples on Jerai Hill.17 morphotypes can be identified in phytolith assambalges,included saddle,elongate,trapeziform,irregularly woody shapes,rectangle,tabular,vascular tissue,square,blocky,rondel,bilobate,cross,silicified stomate,globular,ellipsoidal,cuneiform and cuneiform bulliform cells.Phytoliths derived from Poaceae were significantly sensitive,even over-representative to indicate distribution of Poaceae plants.With the increasing elevations,the major phytolith components slightly varied,which were globular-irregularly woody shape-blocky assemblage in lowland dipterocarp forest,globular-roundel-irregularly woody shape assemblage in hill dipterocarp forest,and globular-block-irregularly woody shape assemblage in heath forest and montane forests.Globular phytolith was very abundant,it's percentages were 82.00%,67.80%,71.10%and 75.10%in lowland dipterocarp forest,hill dipterocarp forest,heath forest and montane forest,respectively.The result showed that phyolith assemblages did not well correspond to various vegetation belts,and most of diagnostic phyoltiths may not be originated from predominated vegetation species.However,phytolith assemblages predominated by globular shapes can be considered as indicators of tropical forests,as this character corresponds with those in African and South American tropical forests.This study confirmed that phytolith assemblages are useful for distinguishing between tropical forests and steppes or savannahs in Southeast Asia.