| Invasion by macrophytes into aquatic ecosystem have the potential to impact macrohyte decomposition via alteration of the microenvironment.However,there is limited information on the effects of aquatic invasive plants which were different life forms on the decomposition of native macrophytes.In the present study,we used litterbags method to investigate the effect of Eichhornia crassipes and Alternanthera philoxeroides on the decomposition rate and nutrient release dynamic of floating macrophytes(Nymphoides peltatum)and submerged macrophytes(Ceratophyllum demersum)and the community of decomposers(invertebrates and microbes).Additionally,we also compared the effects of these two aquatic macrophytes on the decomposition of native plant.The results are as follows:(1)Decomposition rate.The decomposition rate of N.peltatum were significantly greater than that of C.demersum in all habitats.The decomposition rates of both materials were positively correlated with initial C,N,P,phenolics,hemicellulose,C/N ratio and C/P ratio,but negatively correlated with initial cellulose and lignin.The decomposition rates in 5 mm-mesh litter bags were higher than that in 0.5 mm,regardless of plant materials.There were no significantly differences in the decomposition rate of N.peltatum in 5 mm-mesh litter bags and C.demersum in both mash size litter bags between canopies under E.crassipes and open water,while the decomposition rate of N.peltatum in 0.5 mm litter bags were significantly reduced under E.crassipes canopies.The percentage of mass remaining of N.peltatum under E crassipes canopies in 0.5 mm-mesh litter bags increased by 3.47%compared to open water after 60 days.There were no significantly differences in decomposition rate of the two materials in both mesh size litter bags between canopies under A.philoxeroides and open water,The life form of invasive aquatic macrophyte did not affect the decomposition rate of the two materials in both mesh size litter bags.(2)Nutrient release dynamic.The invasion of E.crassipes significantly affected the percentage of P remaining of the two materials,but not for the percentage of C and N remaining.After 60 days,the percentage of P remaining of N.peltatum in two kinds of mesh size litter bags under E.crassipes canopies was reduced by 14.08%and 1.46%compared to open water,respectively,and the percentage of P remaining of C.demersum in two kinds of mesh size litter bags increased and reduced by 4.34%and 13.88%,respectively.The invasion of A.philoxeroides significantly affected the percentage of N remaining of the two materials,but not for the percentage of C and P remaining.After 60 days,the percentage of N remaining of N.peltatum in two kinds of mesh size litter bags under A.philoxeroides canopies was reduced by 22.80%and 36.83%,respectively,and the percentage of N remaining of C.demersum in both two mesh size litter bags increased by 11.39%and 18.55%compared to open water,respectively.The percentage of C and N remaining of the two materials under A.philoxeroides canopies significantly increased,but the percentage of P remaining significantly decreased.The results indicated that both invasive macrophytes affected the nutrient release of N.peltatum and C.demersum,and magnitude were species-dependent.(3)Structure and assembles of macroinvertebrate communities.A total of 10 macroinvertebrate species were collected in litter bags(including 4 functional groups).A total of 7 macroinvertebrate species were collected under E.crassipes canopies,of them,4 macroinvertebrate species were collected in N.peltatum(the number of collecter,scraper and shredder were 1,2 and 3,respectively)and 6 macroinvertebrate species were collected in C.demersum(the number of collecter,scraper and shredder were 1,2 and 1,respectively).A total of 9 macroinvertebrate species(including 4 functional groups)were collected under A.philoxeroides canopies,of them,8 macroinvertebrate species were collected in N.peltatum(the number of collecter,scraper,shredder and predator were 1,2,4,and 1,respectively)and 4 macroinvertebrate species were collected in C.demersum(the number of collecter,scraper,shredder and predator were 1,2,1 and 0,respectively).A total of 8 macroinvertebrate species(including 3 functional groups)were collected in open water,of them,7 macroinvertebrate species were collected in N.peltatum(the number of collecter,scraper,shredder were 1,3 and 3,respectively)and 5 macroinvertebrate species were collected in C.demersum(the number of collecter,scraper,shredder were 1,2 and 2,respectively).The invasion of E.crassipes and A.philoxeroides significantly decreased the abundance and richness of macroinvertebrates.in the bag of two materials.The abundance and richness of macroinvertebrates which colonized in N.peltatum under E.crassipes canopies reduced by 69.04%and 58.63%compared to open water,respectively,and that reduced by 58.51%and 46.15%for C.demersum,respectively.The abundance and richness of macroinvertebrates which colonizd in N.peltatum under A.philoxeroides canopies reduced by 85.84%and 33.99%compared to open water,respectively,and that reduced by 85.54%and 50.00%for C.demersum,respectively.The invasion of E.crassipes and A.philoxeroides decreased the richness of of macroinvertebrates,but increased the evenness of them.However,the abundance and richness of macroinvertebrates had no significantly difference between the two types of invasive plants,but the abundance and richness of the macroinverberates which colonized the both materials changed in different periods.(4)Microbial respiration rates,bacterial CFU and fungal CFU.The invasion of E.crassipes and A.philoxeroides significantly decreased the microbial respiration,regardless of the materials,but did not affect the number of bacterial and fungal CFU.After 60 days,microbial respiration rates of N.peltatum and C.demersum under E.crassipes reduced by 47.97%and 35.56%compared to open water,respectively.The invasion of A.philoxeroides significantly decreased the microbial respiration of the two decomposition materials and the number of fungal CFU colonizing in N.peltatum(P<0.05),but did not affect on the number of bacterial CFU which colonized in the two materials and fungal CFU which colonized in C.demersum.After 60 days,microbial respiration rates of N.peltatum and C.demersum reduced by 33.68%and 53.41%,respectively,and the number of fungal CFU which colonized in N.peltatum reduced by 48.28%,compared to open water.The microbial respiration rates of C.demersum significantly decreased by 49.85%under E.crassipes canopies,compared to under A.philoxeroides canopies.Pearson correlation analyse indicated that under Eichhornia crassipes canopies,the rates of both materials were significantly positively correlated with microbial respiration and the number of fungal CFU,and negatively correlated with the number of bacterial CFU.However,under Alternanthera philoxeroides canopies the rates of both materials were significantly positively correlated with microbial respiration and the number of bacterial CFU,and negatively correlated with the number of fungal CFU.In summary,the invasion of E.crassipes and A.philoxeroides can affect the decomposition of native N.peltatum and C.demersum by influence the structure and assembles of macroinvertebrate,and these effects were invasive species-dependent and decomposition time-dependent.Our study had an important significance for comprehensively understanding the ecological process that the invasive macrophytes affect. |
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