水华衰亡过程中微囊藻群体胶鞘结构及其元素组成的变化

Changes in structure and element composition of mucilage sheath of Microcystis colony during the bloom decline period

维系微囊藻群体结构的胶鞘是微囊藻水华维持优势的重要原因之一.为了探讨微囊藻水华的衰亡机理,在太湖梅梁湾水华衰亡过程中（10月至次年1月）,对微囊藻群体大小的组成做了统计,同时对单位藻细胞的胶鞘多糖产量变化进行了检测,并对微囊藻群体胶鞘的变化进行了能谱扫描电镜观察和元素组成分析.结果表明,随着水华的衰亡,100~180μm的微囊藻小群体的比例表现出增多的趋势,而大于180μm的大群体逐渐减少,单位藻细胞的多糖含量呈现下降的趋势.扫描电镜结果显示了微囊藻群体的胶鞘从完整到逐渐裂解的变化过程,群体表面的能谱化学元素分析显示,钠和磷元素的百分含量呈下降的趋势,铝和硫元素的百分含量趋于稳定,而钙和硅元素的百分含量呈上升的趋势.以上结果说明了微囊藻群体中单位细胞的多糖产量减少,群体胶鞘裂解,元素组成发生变化,伴随着微囊藻群体的解聚,出现水华的衰亡.

Mucilage sheath is critical for maintaining predominance of colonial Microcystis in eutrophic freshwaters. To explore mechanism underlying the decline of Microcystis bloom, colony size, polysaceharide content and sheath structure of Microcystis colonies were investigated from October to January when the bloom decline. The results indicated that the proportion of Microcystis with colony size larger than 180μm decreased, while colonies in the 100-180μm size range increased. Polysaecharide content per cell decreased during the decline period. The scanning electron micrograph showed that sheath structure of Microcystis colonies changed from complete to broken. Element analysis of the surface of Microcystis colonies showed the percentages of Na and P decreased gradually, Al and S fluctuated, while Ca and Si increased. These results indicated that changes in polysaccharide content and element composition of colony sheath accompanied with colonial Microcystis disaggregation, and thus led to bloom decline.