Relationship Between Typical Communities And Topsoil Phytolith Assemblage In Liaodong Peninsula And Its Accuracy In Palaeovegetation Reconstruction

The Liaodong Peninsula is located in the north of the East Asian monsoon region,which is sensitive to climate and vegetation change.It is of great significance to quantitatively reconstruct the evolution history of palaeovegetation in this region for interpreting the past vegetation and climate change.In this paper,based on phytolith we analyzed 211 woody species samples(81 leaf samples,73 branch samples,57 bark sampels),90 typical community samples(30 herbaceous layer samples,30 litter layer samples,and 30 mixed samples of herb layer and litter layer),84 corresponding topsoil samples under typical communities,and 119 profile samples.And a series of phytolith modern processes,such as phytolith source,plant classification level of community phytolith assemblage,identification of vegetation types by topsoil phytolith,the quantitative relationship between topsoil phytolith and community density,have been studied.Then the results studies were applied to Ji An profile to reconstruct the evolution of paleo-vegetation since the middle and late Holocene,and the applicability of phytolith in the reconstruction of paleovegetation in this area was verified by combining with the paleovegetation reconstruction data in the surrounding area.This paper draws the following conclusions:1.In the common woody plants of Liaodong Peninsula,neither branches nor barks produce phytoliths,but leaves mainly produce epidermal phytolith,tracheary,and stomate.The phytolith assemblage can divide the typical plant communities into Pinus-Quercus forest,Quercus acutissima forest and broad leaved forest,which proves that phytolith has the ability to classify the plant communities.By comparing phytolith assemblages in litter layer and herbaceous layer,phytolith assemblages produced only in woody plants and phytolith assemblages produced only in herbaceous plants were determined.Using the ratio of phytolith assemblages(W/G)of the two types,the change of plant community structure could be determined.2.The phytolith production and phytolith assemblage in topsoil were different in different communities.The discriminant function based on all topsoil phytolith assemblage could distinguish Pinus-Quercus forest,Quercus acutissima forest and broad leaved forest effectively,and the discriminant accuracy reached 80%.The Ic index and Iw index had significant differences among the three communities,which were relatively applicable in this region.Based on WA-PLS method,the quantitative relationship between topsoil phytolith assemblage and community density was established,and the predicted vegetation density had a significant linear correlation with the measured vegetation density,which could effectively reconstruct the density of palaeovegetation.3.Based on the correspondence between plant community and topsoil phytolith assemblage,the evolution process of Ji An profile since the middle and late Holocene was reconstructed as follows: 4961-4187 cal a BP,The vegetation type was broad leaved forest with low density,C3 herbaceous plants had more advantages than C4 herbaceous plants,and the ratio of woody and herbaceous plants was relatively large;4187-2400 cal a BP,the change of vegetation type from the broad leaved forest to the Pinus-Quercus forest proved that the number of coniferous plants was relatively increased in this stage,the density was larger,C4 herbaceous plants had more advantages than C3 herbaceous plants,and the ratio of woody and herbaceous plants was relatively small;2400-590 cal a BP,the vegetation types were mainly Pinus-Quercus forest and Quercus acutissima forest,with low density.C3 herbaceous plants were more dominant than C4 herbaceous plants,and the ratio of woody and herbaceous plants was relatively large.The comparison of the palaeovegetation types evolution results,the reconstruction results of palaeovegetation density,the reconstruction results of palaeotemperature and the periodic evolution of vegetation in the surrounding area all proves that the phytolith-palaeovegetation reconstruction results in Ji An section are accurate,and the phytolith-palaeovegetation reconstruction is suitable for the Liaodong Peninsula.