营养盐添加对水华蓝藻——卵孢金孢藻生长和竞争影响的原位实验

为探究在水体营养盐浓度持续增加的条件下,卵孢金孢藻(Chrysosporum ovalisporum)的生长趋势和其它藻类的生长响应,在上海滴水湖畔采用39个大桶(100 L)进行不同浓度N、P添加的原位中型模拟实验.结果表明,高浓度营养盐添加可促进卵孢金孢藻和绿藻生物量的增加,加P组二者生物量的增加趋势高于加N组,但差异并不显著(P0.05),加NP组二者生物量的增加趋势显著高于加N组和加P组(P0.001).在加N组和加NP组,卵孢金孢藻相对丰度随营养盐添加量的增加呈显著的下降趋势(P0.05),而在加P组其相对丰度随着P浓度的增加略有上升,但不显著(P0.05).实验结束时,所有处理组中卵孢金孢藻的生物量不占优势,而小粒径藻类色球藻属(Chroococcus spp.)、空星藻属(Coelastrum spp.)、小球藻属(Chlorella spp.)、四角藻属(Tetraedron spp.)、栅藻属(Scenedesmus spp.)]的生物量随营养盐浓度升高的增加趋势显著高于卵孢金孢藻(P0.05),小型绿藻占据绝对优势,表明在高温和相对静止的条件下,随着水体中营养盐浓度的持续增加,小粒径藻类易替代卵孢金孢藻而占据竞争优势;这与小粒径藻类在高营养条件下代谢速率较高有关,也与绿藻喜静止、高光强的生物学特性有关.小型绿藻占据优势可能成为小型超富营养水体中浮游植物群落在高温季节的演替方向之一.

Effects of Nutrient Addition on the Growth and Competition of Bloom Forming Cyanobacterium Chrysosporum ovalisporum: An In-situ Experiment

An in-situ mesocosm experiment was conducted to study the growth dynamic of Chrysosporum ovalisporum and the other phytoplankton organisms under accelerated eutrophication conditions by using 39 buckets (100 L) in Lake Dishui, Shanghai. The results showed that the growth of both filamentous cyanobacteria (C. ovalisporum) and green algae were promoted with nutrient enrichment. The increase in the algal biomass rate in N plus P addition treatments was significantly higher than in treatments with N or P alone (P<0.05). Although the increasing biomass rate with P addition alone was higher than with N alone, there was no statistically significant difference (P>0.05). The relevant abundance of C. ovalisporum showed a significantly decreasing trend with N addition treatments and N plus P additions treatments (P<0.05), although it was slightly increased with the treatments with P alone (P>0.05). Nutrient addition could significantly improve the growth of small sized algae organisms (Chroococcus spp., Coelastrum spp., Chlorella spp., Tetraedron spp., and Scenedesmus spp.) rather than C. ovalisporum in all treatments (P<0.05). The small sized green algae overcoming C. ovalisporum indicated that small sized algae were more favored by hyper-eutrophicated, high water temperature and relatively undisturbed conditions. This is because small sized algal organisms have higher metabolic and growth rates compared to other sized algae, especially in stationary water regimens and high, light density conditions. We foresee that the small sized algae, Chlorophyte, dominating the small hyper-eutrophic aquatic system may be a potential succession pattern in the high water temperature seasons.