Allelopathic Effects Of Ceratophyllum Demersum On The Growth And Morphology Of Chlorella Vulgaris

In shallow freshwater ecosystems,submerged macrophytes and algae usually compete for nutrients,light and space.Previous studies mainly focused on the growth effects（biomass,growth rate,photosynthetic activities）of algae by submerged macrophytes.The present study found that submerged macrophytes could also have morphological influences on green algae.However,so far,little is known on the mechanisms of this colony formation and which allelochemicals might play roles have not been reported.Based on these backgrounds,in the present study,we used the green alga Chlorella vulgaris and the photosynthetic competitor Ceratophyllum demersum in our experiments.By observing the growth and morphology changes of green alga,we systematically analyzed the interaction between the two photosynthetic organisms according to co-culturing and extract expermentation.Results are as follows:1.Effects of macrophyte extracts and co-cultivation on growth and colony formation of C.vulgaris.The results indicated that both direct contact and extracts of macrophytes could promote colony formation and inhibit the growth of C.vulgaris;High biomass of macrophytes caused the formation of more and larger colonies.In addition,the high biomass of C.demersum treatment corresponded to high intracellular carbohydrate content（IPS）per algae cell.Effects of co-existing macrophyte on growth and colony formation of C.vulgaris was greater than the influence of macrophyte extracts of C.vulgaris.The allelochemicals might play roles in this process and they can be released into the water on the target algae and the active substances might decrease in the experiment.2.Effects of extracts from C.demersum on the growth and morphology of C.vulgaris.Acetone and methanol were used to extract different biomass levels of fresh C.demersum（final concentration,0.17g/mL,0.25g/mL,0.42g/mL,0.75g/mL and 1.25g/mL）and different initial cultivation(OD₆₈₀=0.02,OD₆₈₀=0.05)of C.vulgaris were used.Results showed that extracts of macrophytes could significantly affect the morphology and growth of C.vulgaris.With the biomass of C.demersum continued to grow,the inhibition effects were increased.The 0.75g/mL and 1.25g/mL of macrophytes could significantly inhibit the growth of C.vulgaris.The extraction experiment further proved that allelochemicals in C.demersum could not only affect the growth of C.vulgaris,but also induce its morphology change.Whether these two types of allelochemicals was similar deserved to be further discussed.3.Detection and analysis of acetone and methanol extracts from C.demersum.According to analysis of GC-MS,acetone extracts of C.demersum included hexanoic,azelaic,tetradecanoic,phthalic,octanoic,2-hexenedioic and propanedioic.However,when co-cultivation with C.vulgaris,succinic,hexanoic,phthalic,octanedioic,butenoic,propanoic,butanedioic,acetoacetic,azelaic,hexadecanoic,alpha.-linolenic,pentanedioic and benzeneacetic were detected.Meanwhile,methanol extracts from C.demersum included hexanoic,acetoacetic,azelaic,hexadecanoic,stearic and traumatic.When co-cultivation with C.vulgaris,hexanoic,azelaic,stearic,acetoacetic,10-undecynoic,doconexent,traumatic and5,8,11,14-eicosatetraynoic were determined.All the measured allelochemicals belonged to the group of fatty acids.4.Effects of standard allelochemicals on the morphology of C.vulgaris.We used 6 kinds of standard allelochemicals in our experiments（azelaic,hexadecanoic,stearic,alpha.-linolenic,pentanedioic and hexanoic）.The results revealed that hexadecanoic could significantly induce the colony formation and growth inhibition of C.vulgaris;Stearic and alpha.-linolenic also induced the colony formation of C.vulgaris,the effects of which were less than that of hexadecanoic.Stearic caused significant growth inhibition of C.vulgaris.Azelaic,hexanoic and alpha.-linolenic showed significant promotion effects on the growth of C.vulgaris.