Characteristics Of Phytolith Transport And Preservation Of Typical Soils In Northeast China And Its Application For Palaeoenvironment Reconstruction

Paleoclimatic change is one of the hot topics of today's scientific community.As one of reliable climate proxies,phytolith has made important contribution to paleoclimate study.However,little is known about the present process of soil phytoliths,which would severely impact the accuracy of paleoclimate interpretation.Therefore,considering the closed relationship among soil phytoliths,vegetation and climate,we make a detailed research on the present process of phytoliths in ten typical soils from 139 sampling sites in Northeast China,mainly including source,transport,preservation,etc of soil phytoliths.Thus here we firstly investigate the quantitative relationship between the phytoliths from plant community and soil,and the transport behavior of phytoliths in typical soils.Then combined with climatic factors and soil physical-chemical properties,we examine the preserve mechanism of phytoliths in typical soils.Finally,based on the above research,we use the R value,which means the ratio of phytolith percentage between plant community and soil,to revise the percentage of soil phytoliths.Phytolith transfer function,based on the revised percentage of soil phytoliths,is developed for precipitation.Then we use the phytolith transfer function to reconstruct the qua ntitative precipitation history of NE China since 13.39 cal.ka BP.Conclusions are as follows:(1)The phytolith assemblages from the nine typical soils(exclusive of paddy soil)are similar with each other,particularly in terms of the content of dominated short cell phytoliths,elongate and lanceolate phytoliths.Simultaneously,the phytolith indexes(named lph and Fs)have been proven to be effective in the temperate zone.Then lph and Fs values higher than0.45 and 0.24 respectively are characteristic of meadow steppe,which would provide a reference point for the successful application of Iph and Fs as a proxy in this area.However,there are still some differences on phytolith assemblages and indexes among different soil types.These findings could cover the shortage of soil phytoliths from different plant communi ties in paleoclimate reconstruction.Moreover,phytolith contents and indexes in the zonal soil are sensitive to precipitation,indicating their reliability for paleoenvironment reconstruction.(2)There is a relationship,to a certain extent,between phytolith assemblages of plant community and soil,and soil phytoliths consist of approximately 7.14% information from plant communities.However,information contained by soil phytoliths differs significantly among different soils types,with more information in dark brown soil,chestnut soil and boggy soil.Moreover,according to the indices of A(association index),O(over-representation index),U(under-representation index),C(correlation coefficient)and R(representation coefficient)for each phytolith type,the representation and preservational characteristics of different soil phytoliths are different from each other.The representation and preservational characteristics of the same soil phytolith type also differ significantly among different soil types.Lastly,the representation of soil phytoliths not only is related with the preservational characteristics of soil phytoliths but also the phytolith production of plant communities.Thedata presented herein would help improve the precision of paleoclimate reconstruction,and provide a new way of addressing research into biogeochemical cycle of silicon.(3)According to the indices of T,CT and CT?,about 22% of the phytoliths are transported below the natural soils in NE China.For the six typical soils,transport rate in chernozem and chestnut soil,followed by dark brown soil and Albic soils,are all significantly larger than black soil and alluvial soil,indicating a crucial role of soil type in transport efficiency.These results indicate that phytolith transport must be considered when using the distribution of phytoliths in recent soils for paleoclimate reconstruction.Additionally,phytolith size and aspect ratio have a significant effect on phytolith transport: the phytoliths with largest axis length>30?m,an aspect ratio>2 and largest axis length<20?m,an aspect ratio<2 are all preferentially transported than the forms with largest axis length >30 ?m,an aspect ratio <2.However,compared with the phytolith size and aspect ratio,the transport efficiency of phytolith is more related to the climatic factors-the annual average precipitation,confirming its importance for phytolith transport.(4)The annual average precipitation and soil physical-chemical properties are the main factors influencing phytolith transport and preservation.Under the conditions of the above factors,phytolith preservation is largely associated with the annual average precipitation,soil pH,soil clay content and soil organic matter.Of the primary influencing factors on different phytolith types,our results also show that the preservation of the short cell phytoliths are closely linked to soil clay content,and the preservation of the elongate phytoliths are more sensitive to the annual average precipitation,soil pH and soil clay content.While the preservation of blocky phytoliths changes significantly in response to the annual average precipitation and soil pH.Consequently,these findings will provide the theoretical and methodological support for the research on the biogeochemical cycle mechanism of silicon,also a reference point for reconstruction of palaeoclimate and paleovegetation.(5)The revised soil phytolith assemblages,based on the transport and preservation of the soil phytoliths,reflect the information of plant communities and climatic change more accurately than these of the unrevised soil phytoliths.Simultaneously,a new late-glacial precipitation variation of the studied region(derived using a phytolith transfer function based on the revised soil phytolith assemblages)has been established.In addition,the long-term variations of quantitative precipitation reveal a series of dry events as documented in the Holocene period,which are largely consistent with other regional and extra-regional palaeoenvironmental records.The quantitative precipitation variation also indeed represents the evolutionary history of East Asian summer monsoon.Together with 65°N summer insolation and ENSO frequency,Northern Hemisphere summer insolationcould play a major role in driving the EASM,but an ice-volume from high-latitude,the Atlantic Meridional Overturning Circulation and the positive feedback effect of vegetation still affect the EASM,and ENSO variability may also have contributed to the late-Holocene EASM weakening.