Effect Of Calcium Ion On The Competition Among Four Freshwater Algae Species Under Different Nutrient Conditions

Aquatic ecologists have recognized from long-term researches that competition and ion concentration in water as important biological and abiotic factors affecting algal growth,and many studies have focused on the variation of competition between different algae species of the same type along the nutrient concentration gradient.However,it is common for different types of algae to meet and compete in a natural water ecosystem;moreover,besides nutrient ions,water also dissolves a large number of other ions.Therefore,studying the results of com-petition between the same types of algae and different types of algae along the nutrients and other ions gradient is the key to understanding algae performance and improving the efficiency of aquatic ecosystem management.The Ankang section of Hanjiang River is an important water source of the South-to-North Water Diversion.As one of the sources,its water quality affects the downstream production?life and the health of natural ecosystem.The predominant cyanobacteria in the watershed are Phormidium corium and Microcystis flos-aquae(Wittr).Krichner,while the predominant chlo-rophyta are Chlorella vulgaris and Scenedesmus quadricauda.Because of flowing through mountain areas,the section dissolves a large number of rock components,in which the content of calcium(Ca2+)is relatively high.The article combines nutrients and calcium ions to study the growth and competition re-sults of two kinds of chlorophyta?two kinds of cyanobacteria and blue-green algae under dif-ferent calcium ion concentrations(high calcium?low calcium)and different nutritional lev-els(poor nutrition?medium nutrition?rich nutrition),as well as the changes in the multi-species community structure of the four algae.Experiments were carried out in an artificial climate chamber to determine algae cell density?chlorophyll a,and to calculate specific growth rate?the competition?diversity and other indexes.It is found that:(1)At different calcium concentrations,the algal cell density of the two chlorophyta is positively correlated with the nutriental level,and the average specific growth rate of the two algae at different nutriental levels is ?low calcium>? high calcium,indicating that low calcium is more conducive to the growth of the two algae.The interaction between the two chlorophyta is com-petition,and the analysis of the the results of the Lotka-Volterra competition model shows that:low calcium is beneficial to the competition of Scenedesmus quadricauda under various nutrients,when at high calcium,the two algae can coexist stably under poor and rich nutritions,and the two algae can coexist unstably under medium nutrient concentration.(2)Under low calcium conditions,the algal cell density of the two cyanobacteria is posi-tively correlated with nutrient levels;under high calcium conditions,the algal cell density of Phormidium corium is positively correlated with nutrient levels,while the algal cell density of Microcystis flos-aquae(Wittr).Krichner increase first and then decrease,indicating that relative to the calcium ion concentration,the effect of nutrient concentration on the growth of Phor-midium corium is more significant,while relative to the nutrient concentration,the effect of calcium ion concentration on the growth of Microcystis flos-aquae(Wittr).Krichner is more sig-nificant.The interaction between the two cyanobacteria is competitive,and it is obtained by an-alyzing the results of the Lotka-Volterra competition model that:at high calcium,the Phor-midium corium has a competitive competition advantage at each nutrient concentrations;when at low calcium,the two algae can coexist stably at poor and rich nutrient concentrations,and the two algae can coexist unstably under medium nutrition.(3)The interspecific interaction between cyanobacterial Phormidium corium and chloro-phytal Scenedesmus quadricauda is competitive.Analysis of the results of the Lotka-Volterra competitive model reveals that:at low calcium,the two algae can coexist stably in each nutri-tional state;when at high calcium,the two algae can coexist stably in poor and medium nutrient concentrations,and at rich nutrition,the Phormidium corium competes to exclude Scenedesmus quadricauda.(4)In the experimental communities of the four kinds of algae mixed:at different concen-trations of calcium and nutrient,the abundance of the Scenedesmus quadricauda is the largest,followed by the Phormidium corium,and the abundance of the other two algae decreases with time.In addition,the Shannon and Evenness indexs at high calcium levels are slightly larger than those at low calcium under various nutritional states,indicating that high calcium is bene-ficial to maintain the uniformity and diversity of species.These results suggest that the growth and competitiveness of algae are significantly limited by species?calcium ions and nutrient levels.At present,due to atmospheric depositon as well as the input of highly nutrient water and so on,eutrophication of natural water has become an im-portant environmental problem.Therefore,calcium ion in water is an important basis when the constructing and implementing water bloom prevention measures.It should be pointed out that in this research,only calcium ion was used to study the inter-action effect of water nutrition and other ions in the performance of algae.In order to fully un-derstand the growth dynamics of algae and continuously improve the efficiency of water man-agement,the influence and mechanism of other ions,especially the ions with high concentra-tion and heavy metal ions in the water,still need further study.