东海原甲藻与中肋骨条藻的种间竞争特征

对东海原甲藻和中肋骨条藻按照起始Chl-a比1∶5、1∶1和5∶1进行了f/2条件下的共培养实验,以探讨这两种藻的种间竞争特征。实验结果表明在共培养体系中,中肋骨条藻完全占优势,而东海原甲藻的生长受到明显的抑制。应用Lotka-Volterra种间竞争模型对共培养实验进行模拟的结果表明,东海原甲藻与中肋骨条藻的种间竞争结果与初始密度配比无关,中肋骨条藻总会竞争胜过东海原甲藻。为了探讨他感作用对东海原甲藻和中肋骨条藻种间竞争的影响,采用了中肋骨条藻的无藻细胞滤液来进行培养实验。实验结果显示,中肋骨条藻滤液对东海原甲藻及其本身的生长均无明显影响,这表明他感作用并非中肋骨条藻获得优势的主要竞争方式。

Inter-specific competition between Prorocentrum donghaienseand Skeletonema costatum

Prorocentrum donghaiense and Skeletonema costatum are two most typical red tide species in the East China Sea.They can coexist in natural phytoplankton community,but during algal blooms,P.donghaiense blooms are frenquently observed following S.costatum blooms.Many studies have been conducted to clarify the relationship between these two species,but until recently,the mechanism controlling the bloom succession between S.costatum and P.donghaiense is still not resolved.In order to examine the competition between these two species and the effect of allelopathy,this study conducted series bi-algal culture experiments and filtrate experiments. The bi-algal experiments of P.donghaiense and S.costatum were conducted in f/2 medium.The initial ratios of Chl-a of the two algae were 1∶5,1∶1 and 5∶1,respectively.Experimental results showed that S.costatum suppressed P.donghaiense and become completely dominant in the bi-algal culture.The growth tendency and the maximum growth rate μ of in the bi-algal culture were similar.On the contrary,the growth of P.donghaiense was significantly suppressed by S.costatum from the 5th day and its average maximum cell density in the bi-algal culture was much lower than that in its mono-culture.The results showed S.costatum might have a superior survival strategy to P.donghaiense. To invesgate the interaction betweem P.donghaiense and S.costatum in the bi-algale culture,Lotka-Volterra model was applied to simulate our results.The simulated results showed that the carrying capacity(K) and growth rate(r) of S.costatum were much higher than that of P.donghaiense,and S.costatum apparently inhibited growth of P.donghaiense in the bi-algal culture.The model indicated that S.costatum would always outcompete P.donghaiense in the bi-algal culture,and initial cell densities induce little effect on the competitive outcome,which matchedthe experimental results. In order to study whether allelopathy could affect the competition between these two species,the filtrates of S.costatum cultivated under f/2 medium were used to incubate P.donghaiense and S.costatum,The results indicated that under f/2 level,N/P=40 level and N/P=120 level,both P.donghaiense and S.costatum in filtrate cultures exhibited the same growth trends as their controls.Therefore,S.costatum filtrates induced little allelopathic effect on the growth of P.donghaiense and itself,and the result might suggest allelopathy was not the critical mechanism for S.costatum to achieve dominance. In this study,concentration of nutrients in bi-algal and mono-algal cultures was analyzed.The results showed that in bi-algal cultures,nutrient uptake curves,especially the PO4-P uptake curve,wersimilar to those of S.costatum in mono-algal cultures.This similarity might imply that,the advantaged physiological characteristics of S.costatum,such as higher growth rate,and superior adaptability to absorb nutrients,could contribute for it to outcompete P.donghaiense.In addition,as a sticky algae,S.costatum might inter-specificly coagulate and then remove P.donghaiense from the culture medium..