Allelopathic Inhibition Of Cyanobacteria By Three Kinds Of Arbor Defoliation Extract And Their Mechanism

With the development of industry and growth of population,large amount of nutrient in domestic sewage and industrial wastewater is discharged into rivers,lakes and seas.This causes frequent outbreaks of algae,especially for cyanobacterial blooms,with large influence area and long lasting impact,which is one of the most serious global environmental problems and also an urgent issue to be solved today.Thus,it is extremely neccesary to find good,cost-effective,and efficient disposals for algae pollution controlling.In the perface of this dissertation,allelopathy inhibition with the controlling mechanisms of plants and allelochemicals on algae were firsty discussed.The effects of defoliation extract from three kinds of arbor plants?Dracontomelon duperreanum;Litchi chinensis;Magnolia denudata?on algae growth were introduced.The optimal concentration of defoliation extract to control algae was established through comparing algal growth inhibition rate.The photosynthetic activities of Microcystis aeruginosa in three kinds of arbor plants defoliation extract were investigated by determining photosynthetic parameters,namely the maximal quantum yield?Fv/Fm?,effective quantum yield?Y??of PSII,the maximal relative electron transport rate?rETRmax?,light saturation coefficient?Ik?,photosynthesis efficiency?alpha?.The microalgae cell membrane integrity,chlorophyll fluorescence,intracellular esterase activity,cell differentiation,and other physiological activity by defoliation extract were investigated by flow cytometry.Changes of fluorescence spectra properties demonstrated different defoliation extract and concentration on algae growth process.At last,the allelopathic antialgal compounds were separated and speculation in the three kinds of arbor plants defoliation by GC-MS.The major findings of the project were as follows:?1?The D.duperreanum defoliation extract?DDDE?has strongest inhibitory effect on algal growth followed by L.chinensis,and the weakest is M.denudate.The inhibitory rate of M.aeruginosa was about 99.6% on day 15 when exposed to 2.0 g·L^-1?dry weight?DDDE,about 82% in L.chinensis defoliation extract?LCDE?,and 77% in M.denudate defoliation extract?MDDE?respectively.The Chl-a concentration of M.aeruginosa was only 19 ?g·L^-1 on day 15 when exposed to 2.0 g·L^-1 DDDE.While that of LCDE and MDDE was still high,which was about 850 ?g·L^-1 and 1220 ?g·L^-1 respectively.The EC₅₀ values were small in the all extracts of defoliation and the smallest was D.duperreanum,followed by L.chinensis and M.denudate.?2?Studies on the photosynthesis of algae showed that arbor plants defoliation extract could inhibit the rapid photosynthesis-irradiance response curve?rapid light curve,RLC?and DDDE could strongly inhibit the electronic relative transfer rate of algae,followed by L.chinensis and M.denudate defoliation.The highest inhibitory capacity was obtained from day 1 to day 7 and gradually increased.The D.duperreanum extract inhibition ability and time was slightly longer than in L.chinensis and/or M.denudate defoliation.?3?The membrane integrity of algal cells was studied by flow cytometry,which presented that the mechanism of all arbor plants defoliation on algal growth control was algistatic in nature rather than algicidal.The intensity of Chl-a fluorescence decreased significantly with high concentration of defoliation extract treatment,which might be the key damaging effect on the photosynthetic system of algae by the allelochemicals in three kinds of defoliation extract.Higher proportion of algal cells collapse occurred with exposure of higher concentration of DDDE(2.0 g·L^-1)on day 15,while that of the normal and the control algal cells was 18.2% and 70.5% respectively.Morphological study revealed that collapse was one of the mechanisms to inhibit algae growth.?4?The excitation-emission matrices?EEMs?fluorescence spectra showed that effects of three kinds of arbor plants defoliation extract on algae growth were similar.Fluorescence peaks of tryptophan and tyrosine acid which were secreted by cyanobacteria were obtained in the control,while in treatment group,humic acid like fluorescent substance other than tryptophan and tyrosine acid appeared.Fluorescence peak intensity and positions of the tryptophan and tyrosine which were closely related to M.aeruginosa growth were inhibitted by high dose of defoliation extract effectively.Fluorescence peak intensity of humic acid gradually became weak over time,which might due to degradable of allelochemicals in the defoliation extracts.?5?Many kinds of suspected allelochemicals were found in the three kinds of arbor plants defoliation extract by GC-MS.The organic acids were abundant in DDDE,which were speculated with the important role against M.aeruginosa.In addition,it also showed that n-Hexadecanoic acid in DDDE and LCDE had strong inhibitory effect against algae.In LCDE and MDDE,the majority were alcohols,ketones,esters and sulfur compounds,of which the potential algistatic characteristic on algae growth is worth further studing.