The phytoliths produced by higher plant is an important tool in the study of paleoclimate and paleoenvironment,which can be employed to reconstruct the terrestrial vegetation changes in the past.There is an increase in studies of phytolith records for reconstructing pre-Quaternary vegetation changes that links to the climate change and carbon cycling.It has therefore been becoming a hot topic worldwide.In fact,the phytoliths in soils,rivers,and coastal areas are also a kind of reactive silica that deeply participates in the global silica cycle,balancing the CO_2 concentrations and controlling the carbon sequestration.Accumulations of phytoliths in the soil are a major reactive silica pool in land,and also a source of riverine biogenic silica.Basin processes could transport part of phytolith from the soil to river,which always was neglected by the previous studies of silica cycling.The transport of phytolih silica in rivers plays an essential role in the local and global biogeochemical cycle processes,and results in long-term ecosystem effect in the ocean margin.Based on the available studies,the river-borne biogenic silica is normally composed by the one from autogenic source produced by the diatom and external source yielded by phytoliths from land soils.As a case study about the Changjiang River and the Huanghe River,the phytoliths could contribute approximately 50% of loading to that of the bulk biogenic silica,which should be included in the silica budget in the river.Damming in the Changjiang and the Huanghe Rivers results in a decline in the loading of riverine biogenic silica,and may thus alter the composition of biogenic silica in the estuary.Therefore,there is a need to bring the phytoliths into the silica cycling research in the river.However,specific pathways and mechanisms governing the abundance,transport and fluxes of biogenic silica from different sources remain poorly understood in the river system.The study of biogenic silica from different sources,the chemical behavior of phytoliths in the river and estuary and the contribution of phytoliths to local silica cycling would have important significance in exploring the silica cycling in river-estuary systems,especially for the huge river in the world.And,the variation of phytoliths in sediments in the coastal zone could provide useful information in assessing damming effect.These works would be needed for better understanding of global scale biogeochemical cycles of silicon and other elements as well as the changing estuary environment.