The Interaction Between Macro-algae And Micro-algae And Its Responses To Enriched CO₂

In recent years more and more attention has been paid to the global change and its concerning research.The ecological effect that global change causes is one of the hot spots in academic circles.The research in the influence of enriched CO₂ concentration to ecosystem was started earlier.And certain results had been achieved. However,the interaction between macroalgae and microalgae with CO₂ enrichment was less researched.On the other side,the red tide occured frequently,which made it increasingly urgent to seek an effective method to prevent and control red tide.This expedited one new method:biology controlling,which is useful and environmental sound.So in this paper two microalgae(Heterosigma akashiwo and Prorocentrum donghaiens),which most often causes red tide in our country and five macroalge(Ulva pertusa,Enteromorpha compressa,Gracilaria verrucosa, Chondracanthus intermedius and Sargassum thunbergii) were chosen to be tested. The test was carried out to study the microalgae's swing of the pendulum within the co-culture system through indoor simulated experiment.Preliminary analysis of the antiblastic mechanism,originating in the inter-competition between macroseaweed and microalgae,was drawn to provide fundamental data support for the prevention and control of red tide.And some basic explanations were also worked out to account for the influence of CO₂ enrichment on this biological method to control red tide.The main results were as follows:1.During the normal test and the test with a high concentration,the growth of the two microalgae was strongly inhibited by fresh tissues and dry powders of the four macroalgae except the ones of Chondracanthus intermedius.And the dry powders had a relatively stronger inhibition with a relatively higher inoculation.2.The inhibitive effects of the macroalgae on the microalgae had a linear relevance with inoculating concentration.Higher concentration of fresh tissues or dry powders meant stronger effect. 3.On the condition that the resources competition was eliminated as far as possible,the macroalgae's allelopathic founctions were mainly taken by direct contact and allelochemicals secreting by macroalgae cells.The fresh tissues were the mixture of the two ways while the dry powders mainly centralized the direct action of allelochemicals.4.The elevated CO₂ could without exception accelerate the growth of all algae, the macro- and also the micro- ones.But the difference lied in motivational time.5.CO₂ with a high concentration greatly affected the allelopathic effectiveness between macroalgae and microalgae.Enriched CO₂ stimulated more allelochemicals to generate in macroalgae fresh tissues,which showed obvious inhibition to microalgae in the first 1-2 days of the test.That was to say,on the one hand,cells number of microalgae fell but not completely disappeared.And on the other,similar phenomenon didn't emerge in the co-culture system of dry powder and microalgae. There was no visible change occurred on the dry powders.6.Effects that macroalgae had to prevent microalgae from multiplicating was different from the ones in normal condition.According to EC₅₀,the effects of Chondracanthus intermedius was a bit stronger while the other four macroalgae decreased in effects.So this raised the difficulty in preventing and curing the red tide.7.At the end of the test,different macroalgae had better inhibitive effects were chosen.And the result was as follows:Fresh tissues of Enteromorpha cornpressa and Sargassum thunbergii were the most effective in keeping Heterosigrna akashiwo from growing.And dry powders of Enteromorpha compressa and Ulva pertusa showed the strongest inhibitive effects on Heterosigma akashiwo.Fresh tissues or dry powders of Ulva pertusa and Enteromorpha compressa were the top two macroalgae in preventing Prorocentrum donghaiens red tide.