Temporal variations of cobalt bioaccumulation in marsh plants of Phragmites australis and Cyperus malaccensis in the Minjiang estuary
Estuarine marshes,located in land-sea interaction zone,are important sources,sinks or converters of trace beneficial elements.As affected by complex environmental changes and human activities in estuaries,it is significance to explore the bioaccumulation for trace beneficial elements by marsh plants.To investigate the temporal variations of cobalt(Co)bioaccumulation in different marsh plants in Shanyutan of the Minjiang estuary across a year and explore its key influencing factois,the typical Phragmites australis marsh(PAM)and Cyperus malaccensis marsh(CMM)were studied.Results showed that the average Co content in marsh soils of the study region throughout a year((13.47±1.50)mg·kg-1)was significantly higher than the background value in topsoil of the Fujian Province(7.41 mg·kg-1),indicating moderate soil enrichment.The temporal variations of Co content in different soil layers of PAM and CMM in whole year were similar,with abrupt decrease from January to April,slight changes during May to September,and rapid increases from October to December.Except for the 0～10 cm depth,the Co contents in soils at 10～60 cm depths in the CMM were significantly higher than those in the PAM(p＜0.05).Both plant growth rhythm and soil depth influenced variations of Co contents in soils of PAM and CMM.roots of P.australis(PA)and C.malaccensis(CM)exhibited significantly higher Co accumulation and bioconcentration factor(BCFCo)compared to other organs,indicating that root was an important organ for Co accumulation.The BCFCo in roots,leaves and standing litters of PA and CM generally increased from January to June,followed by diverse fluctuantions,influenced by plant growth rhythm of different plants and their bioaccumulation capacities for Co.Both marsh soils of PAM and CMM acted as important reservoirs for Co,which accounted for more than 99.7％of the total Co stock in plant-soil systems.Significantly higher Co contents,stocks and BCFCo of Co in organs of CM compared to PA,implying that the CM showed higher bioaccumulation capacity for Co.
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