Distribution Characteristics Of Silica In Plant-soil Systems In The Min River Estuary

Estuarine tidal marshes have recently been considered as an important surface of silica recycling at the land-sea interface.Soil available silica(ASi)is beneficial to the growth of marsh plants,and plants in turn will promote the silica accumulation in soils.The variation to silica in plant-soil systems of typical communities and ecotones is important to reveal the competitiveness mechanism from the perspective of silica cycling in tidal marsh,and to improve the theory of biogeochemical cycling of silica in estuarine marsh ecosystems.In this study,the Min River estuary,located in the southeast of China,was selected as the study area.By field sampling and laboratory experiment,the accumulation characteristics of biogenic silica(BSi)in the main marsh plant species(Phragmites australis,P.australis + Cyperus malaccensis,C.malaccensis,C.malaccensis+Spartina alterniflora and S.alterniflora),the variations of ASi content and its influencing factors in marsh soils were analyzed,and the biological cycling processes of silica in the plant-soil systems were also summarized in the estuarine marsh ecosystems.The main results showed as follows:(1)BSi content in different organs of P.australis was higher than that of C.malaccensis and S.alterniflora,with the mean value of 27.42,18.69 and 15.52 mg·g-1,respectively.In contrast to C.malaccennisis,BSi content of P.australis and S.alterniflora was lower in ecotones than in typical communities.Generally,BSi content of litter in three marsh plants was higher than that of other organs,and BSi content in roots was lower than that in aboveground parts.(2)The total BSi stock in marsh plant species showed the order of P.australis>S,alterniflora>C.malaccensis and BSi stock in different organs of three plant species in ecotones was lower than in typical communities.BSi stock allocation to roots and stems of the three plant species was higher than other organs,indicating that roots and stems were the main BSi pool in marsh plants.BSi allocation in different organs of marsh plants in ecotones was differed.(3)BSi content in the surface soils of different types of marshes fluctuated along with the time,and BSi content in ecotonal marsh soils was higher than that in typical community marsh soils.(4)Seasonal variation of soil ASi content was showed a fluctuated trend in the Min River estuary.ASi content generally increased from land to sea in the horizontal direction.ASi content in P.australis dominated marsh and P.australis + C.malaccensis marsh showed the decreased trend with increasing depth,while ASi content in C.malaccensis +S.alterniflora marsh and S.alterniflora dominated marsh increased with increasing depth.No obvious change of ASi content in C.malaccensis dominated marsh was observed.(5)Soil temperature,bulk density and electrical conductivity were the main factors influencing ASi content in the Min River estuary.The absorption,utilization and return by plants,the dissolution by plant roots and its vertical migration had important effects on distribution of ASi in the marsh soils.And hydrological conditions such as innudation also importantly influenced the variation of ASi content.The distributions and its influence factors of ASi content in marsh soils in both typical communities and ecotones of the same plant species were significantly differed under different environmental conditions.(6)The soil BSi stock was the main part of BSi pool in the plant-soil systems.The annual absorption,retention,restore,and standing stock of BSi were the highest in P.australis,followed by S.alterniflora and C.malaccensis;meanwhile,the above indicators of three plant speices were higher in typical communities than in ecotones.(7)The absorption coefficient of BSi in marsh plants was higher than the utilization and recycle coefficient.The absorption and recycle coefficient were the highest in P.australis while the utilization coefficient was the greatest in S.alterniflora.The absorption coefficient to BSi of three plant species in typical communities was higher than in ecotones while the utilization and recycle coefficient showed an opposite trend.