Phytolith Morphology Of The Tropical Plants And Their Environmental Implications

During the Last Glacial Maximum(LGM),the presence of a steppe or lowland rainforest on the emergent Sundaland in Southeast Asia was proposed by many researchers.This uncertainty impairs our understanding of the role of vegetation changes in carbon cycling in orbital-scale,because tropical rainforests and associated peatlands can assimilate much more carbon than steppes,reducing CO2 concentration in the atmosphere.Unfoturenaly,plants in the tropical region are mostly insect-pollinated and have low pollen productivity,resulting in that pollen fossil cannot comprehensively reflect the vegetation information.Therefore,we need to develop a new paleovegetational proxy to solve the problem of underrepresentation of tropical pollen.The phytolith analysis is a crucial tool for reconstruction paleoenvironment and paleovegetation,however,rare phytolith research were carried out in Southeast Asia,which hinders accurately paleovegetational reconstruction during the LGM.In this study,we analyzed 14 topsoil samples from different elevations,and 119 modern plant samples belonging to 99 plant species.Plant samples are composed of 41 leaf samples belonging to 39 species and 78 herbarium samples belongs to 60 species,which are collected from Jerai Hill and Universiti Sains Malaysia,respectively.All analized plants are popular on Jerai Hill.The purpose of study is to evaluate the potential of phytolith assemblages as proxies for implying various paleovegetation types in Southeast Asia.Jerai Hill is located in Kedah State of Peninsular Malaysia.The summit of the highest mountain is at 101°26? E,05°47? N,and the maximum elevation reaches 1217 m,the typical vegetation type is the rainforest rich in Dipterocarpaceae species.With the increase in elevation,plant communities evidently change,particularly the species abundance 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.Both topsoil and modern plant samples were extracted by using wet oxidation method.The heavy liquid used to extract topsoil phytoliths was composed of Zn grains,potassium iodide,and hydroiodic acid,and specific gravity was set to 2.385.The following conclusions could be made::(1)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.(2)With the increasing elevations,the major phytolith components slightly varied,which were globular-irregularly woody-blocky assemblage in lowland dipterocarp forest,globular-roundel-irregularly woody assemblage in hill dipterocarp forest,and globular-blockirregularly woody assemblage in heath forest and montane forests.Globular phytolith was very abundant,it's percentages were 82%?68%?71% and 75% in lowland dipterocarp forest,hill dipterocarp forest,heath forest and montane forest,respectively.(3)The morphological types of phytolith of modern plants varied along families,genera and species.17 morphotypes can be identified in 41 plant samples collected from Jerai Hill,included epidermal cell,silicified stomata,vascular tissue,polylobate,irregularly shapes,elongate,hair cell,hair base,globular granulate,cuneiform bulliform cells,saddle,bilobate,cylindrical polylobate,sclereid cell,globular echinate and two unknown types.Furthermore,17 morphotypes were also found in 78 herbarium samples collected from the area around the Jerai mountain,included vascular tissue,silicified stomate,epidermal cell,elongate,irregularly shapes,sclereid cell,hair cell,rectangle,globular granulate,globular echinate,tabular,hair base and five unknown types.(4)Phytolith assemblages predominated by globular shapes did not well correspond to various vegetation belts,and most of diagnostic phyoltiths may not be originated from unconstructive species,while dipterocarp forest,which was the constructive species,did not produce phytoliths with diagnostic characteristics.Therefore,phytolith assemblages predominated by globular shapes can be considered as an indicators of non-constructive species,such as Palmae and Myrtaceae.Compared with the phytolith assemblages in temperate,subtropical and tropical arid and semi-arid regions,those phytoliths derived from nonconstructive species still had unique characteristics,which was strongly representative of the tropical rainforest climate.(5)Phytoliths derived from Poaceae on Jerai Hill were significantly sensitive to indicate distribution of Poaceae plants,which makes phytolith a useful indicator for distinguishing between tropical forests and savannahs.This study confirmed that phytolith analysis has important application value for reconstruction paleovegetation in Southeast Asia.