起始生物量比对3种海洋微藻种间竞争的影响

Abstract

The investigation of interspecific competition is useful to reveal the mechanism in regulating growth and reproduction of organisms,optimal control of harmful organisms and co-culture of beneficial organisms.The interspecific competition is influenced by either population density or body size,therefore it is important to investigate the effects of biomass on the interspecific competition. A method of co-culturing microalgae was used to examine the effects of initial biomass ratio(1∶4,1∶1 and 4∶1) on interspecific competition between three marine microalgae species,Alexandrium tamarense,Isochrysis zhanjiangensis and Chlorella pyrenoidosa in the present experiment.The mixed algae in the exponential growth phase were cultured to increase cell density in 250 mL erlenmeyer flasks containing 150 mL of f/2 culture medium.The temperature was maintained at(20±1) ℃,and flasks were illuminated in a photoperiod of 12L—12D with a light intensity of approximately 1000 lx.The salinity was(31±0.5) and pH was 8.34.After 20 days culture,the densities of algal cell(algal cells/ml) were measured with OlympusCX21 microscope.Moreover,logistic growth curve was fitted to calculate the competitive inhibition parameters based on the cell densities. The results mainly suggested the following points: 1) the inhibition effect of interspecific competition between three microalgae was significantly related to the environmental carrying capacities(K);2) during the process of competition with A.tamarense(A),both C.pyrenoidosa(C) and I.zhanjiangensis(I) were dominant algae.With the increase of initial biomass,C.pyrenoidosa showed the increasing competition advantage.When the biomass ratio of A to I was held at 1∶1,I.zhanjiangensis was obviously super-dominant.When the ratio of C to I was 1∶4,I.zhanjiangensis was the dominant algae.When the ratio of C to I was 1∶1,I.zhanjiangensis was competitively dominant in the earlier stage,but C.pyrenoidosa grew faster,superseding I.zhanjiangensis in the later stage.When the ratio of C to I was 4∶1,C.pyrenoidosa was predominant;3) based on the competitive inhibition parameters,the interspecies competitive ability of three species of microalgae were as follow: C.pyrenoidosa I.zhanjiangensis A.tamarense.Furthermore,their competitive ability significantly depended on the algal cell size. The above results suggested that equal ratio of C.pyrenoidosa to I.zhanjiangensis was suitable to co-culture and then utilize in the marine economic animals aquaculture.Moreover,they could also inhibit the growth of A.tamarense.This might be used to control the harmful algae bloom.It was speculated that the inhibiting effect of C.pyrenoidosa and I.zhanjiangensis on the growth of A.tamarense was mainly due to the competition of nutritional sources,while the inhibiting effect of A.tamarense on the growth of C.pyrenoidosa and I.zhanjiangensis was caused by both the direct contact of cells and secondary secretion of toxic substances.