| Wetland is the transition zone between terrestrial ecosystem and aquatic ecosystem,which plays an important role in the maintaining of global material circulation and energy flow,as well as the water purification and environmental protection functions.It is known as the kidney of the earth.Wetlands are also highly productive,although they cover only 4-5 percent of the earth's land surface,their carbon reserves account for about 20 percent of the whole biosphere.As an important step to keep wetland stability,a large amount of wetland biomass participates the nutrient cycle with the manner of yearly litter decomposition.Compared with forest and marine ecosystems,wetland ecosystems have a higher ecological sensitivity to global environmental changes,and which severely impacts wetlands and their carbon storage functions.Especially in some high throughput lake wetlands,the changed seasonal hydrological regime has a great influence on the litter decomposition process,but the detailed research in such wetlands is insufficient at present.Therefore,this study took the Poyang Lake wetlands as an example,and studied the litter decomposition process by in situ litter bag method,three dominant wetland plants were selected: Carex cinerascens(A),Triarrhena lutarioriparia(B)and Phragmites australis(C).In this study,we aimed to study: 1)the decomposition differences of single species litter and mixed litters;2)the contribution of soil fauna to litter decomposition,and 3)the Home-field Effects of different litters.During the experiment,the decomposition rate of litters,the dynamics of nutrient release(carbon,nitrogen and phosphorus)and the degradation of refractory components(hemicellulose,cellulose and lignin)were monitored,and the dynamic changes of extracellular enzyme activity and bacterial community structure during the decomposition were also observed.The results of this study are as follows:(1)The decomposition difference between single species and mixed litters was obvious,and this difference is closely related to the substrate quality of litters.Among the three single litters,C.cinerascens had higher nitrogen content,low C:N ratio and lignin content,and is a high-quality litter with rapid decomposition.By contrast,T.lutarioriparia was a low-quality litter with slow decomposition.The antagonism or synergistic effect of mixed litters depend on the quality of involved single species.The mixed litter of C.cinerascens and T.lutarioriparia(AB),the mixed litter of C.cinerascens and P.s australis(AC),and the mixed litter of all three species(ABC)generated synergistic effects;while the mixed litter of T.lutarioriparia and P.australis(BC)generated antagonistic effects.Meanwhile,the mix of different litters could promote the release of carbon,nitrogen and phosphorus and the degradation of hemicellulose,while cellulose and lignin were degraded faster in single litter.The extracellular enzyme activity increased first and then decreased during decomposition,and the highest activity occurred at the 90 th day.The mixed T.lutarioriparia and P.australis litter(BC)had higher enzyme activities of Bglu,Bxyl and CB.The bacterial community diversity at 165 days was higher than that at the beginning of decomposition,and litter mix could improve the diversity of bacterial community.The bacterial community composition was related to the litter property.Firmicutes were often abundant in a single specie litters and Bacteroidetes were abundant in mixed groups.Litters containing C.cinerascens often had higher abundance of Proteobacteria and Actinomycete.Litters containing T.lutarioriparia and/or P.australis had higher abundance of Cyanobacteria.(2)Soil fauna can promote the decomposition of litter,accelerated the degradation of lignin,cellulose,hemicellulose,and speeded the release of carbon and phosphorus.Soil fauna contributed more than 30% in the initial stage of decomposition and more than 10% in the later stage.Although soil animals had no significant effect on extracellular enzyme activity,it affected the structure of bacterial community.Soil animals not only improved the diversity of bacterial community,but also increased the abundance of Actinobacteria,Bacteroidetes and Firmicutes,which were conducive to the decomposition of litters.(3)The Home-field Effect of litter decomposition was related to the litter and bacterial community structure.The lower of the litter quality and decomposition,the more obvious of the home field advantage.The better of the litter quality,the less obvious of home field advantage.C.cinerascens and T.lutarioriparia had home-field advantage when they decomposed at their origin habitats,and was more obvious for T.lutarioriparia;while P.australis did not have the advantage,and decomposed quickly in the T.lutarioriparia habitat.The home-field advantage could promote decomposition,accelerated carbon release and the degradation of hemicellulose,cellulose and lignin.The enzyme activity was significantly enhanced for C.cinerascens and T.lutarioriparia litters when they decomposed at their origin habitats.When C.cinerascens litter decomposed at home field,the bacterial community diversity was lower than other sites,and higher abundance of Actinomycete and Firmicutes,lower abundance of Bacteroidetes were found.When T.lutarioriparia litter decomposed at home field,the bacterial community diversity was higher than other sites,and the bacterial community structure was similar with above mentioned C.cinerascens.The highest bacterial community diversity of P.australis litter was found in T.lutarioriparia habitat,and higher abundance of Proteobacteria and Bacteroidetes,lower abundance of Actinomycete and Firmicutes were observed.In summary,litter mixing mainly changes liter quality and resulting in different decomposition characteristics.Soil fauna can promote litter decomposition and accelerate the circulation of nutrients.The Home-field Effect of litter decomposition is related to litter quality and bacterial community structure,and only happen in some species.The bacterial community diversity increased in the later stage decomposition,and indicated a complicating process of bacterial community structure during decomposition.The litter property and soil fauna can significantly affect the diversity and composition of bacterial community,and further regulate the activity of extracellular enzymes,which play an important role in the nutrient release and degradation of lignin and cellulose.The results of this study disclosed the decomposition characteristics and nutrient elements dynamics of wetland litters with different influencing factors in a typical high throughput freshwater lake,which also deepened our understanding of the role of microorganisms in the decomposition process.The combination of traditional litter bag method and the emerging environmental microbiome technology can provide a strong technical guarantee for the future study of wetland litter decomposition.At the same time,the results of this study are also conducive to the assessment of the health trend of wetland ecosystem,and helpful to the scientific management of lakes and wetlands. |
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