Effects Of Limnodrilus On Decomposition Of Different Aquatic Plants

The decomposition of aquatic plants can cause large-scale fluctuations of water quality and thus affects the ecological functions of the water ecosystem.The decomposition of aquatic plants is influenced not only by abiotic factors but also by biological factors(benthos,etc.).The current studies about aquatic plants decomposition usually focus on the effects of abiotic factors but neglect the role of biological factors.There are few related research about zoobenthos and decomposition of aquatic plant but most of them are scrappers and shredders,collectors are rare.The effects of Limnodrilus on the decomposing process of the emergent plant Phragmites australis,the submerged plant Elodea canadensis,and mixed plant litter were studied in this paper.The rate of decay of aquatic plants,the nutrient elements of plant litters,the quality of overlying water,and the changes of bacterial and fungal community structure and diversity were monitored,the results show that:(1)The Limnodrilus can significantly promote the decomposition of E.Canadensis litter(P<0.05)and it can also significantly promote the decomposition of P.australis litter,from day 33 to day 128.From day 65 to day 128,with the existence of Limnodrilus,the decomposition rate of mixed plant litter was highly significantly enhanced(P<0.01).When the Limnodrilus was in decomposition system,the time for decomposition 50%litter of E.Canadensis?P.australis and mixed plant was shortened from 9 day,129 day and 26 day to 4 day,102 day and 23 day,the time for decomposition 95%litter of E.Canadensis?P.australis and mixed plant was shortened 92 day,704 day and 355 day to 54 day,562 day and 279 day.(2)The mass loss of plant litter was positively correlated with the total nitrogen and total phosphorus content of the initial plant litter and negatively correlated with C/N and C/P.The C/N of E.Canadensis litter with Limnodrilus was significantly lower than that of without Limnodrilus(P<0.05).The content of total phosphorus in P.australis with Limnodrilus was significantly higher than that of without Limnodrilus(P<0.05).The C/P of mixed plant litter with Limnodrilus was significantly lower than that of without Limnodrilus(P<0.05).(3)From day 33 to day 64,the concentrations of COD and TP in the water of Limnodrilus system were significantly higher than those without Limnodrilus(P<0.05).However,from day 65 to day 128,the COD and TP concentrations in the water of Limnodrilus system were lower than those without Limnodrilus and the content of organic carbon,phosphorus in the sediment of the decomposing system with Limnodrilus were significantly higher than that of the system without Limnodrilus(P<0.05).So,from day 33 to day 64,the Limnodrilus can promote the release of C and P from the plant litters into the water body and promote the migration of C and P into the sediment.(4)With the progress of aquatic plant litters decomposition,the richness and diversity of bacterial community of plant litters superficial sediment and Limnodrilus gut increased significantly.The Limnodrilus decreased the richness and diversity of bacterial community of plant litters superficial sediment.At the level of the Phylum,Proteobacteria,Bacteroidetes and Firmicutes dominates;At the level of the Order,the predominant microflora of Limnodrilus gut and plant litters superficial sediment are Clostridiales,Fusobacteriales,Bacteroidal,Rhodocyclales and Desulfobacterales;At the level of the Genus,abundant cellulose degraded bacterium Leadbetterella and Paracoccus were only found in Limnodrilus gut.(5)The richness and diversity of the fungal community in Limnodrilus gut were significantly higher than those in plant litters superficial sediment.Chytridiomycota,and Cryptomycota are the dominant flora on plant litters superficial sediment.Cryptomycota,Ascomycota,Chytridiomycota and Basidiomycota are the predominant microflora in Limnodrilus gut.