| The emergent plant is the important vegetation type in the marshes.The litters from the aboveground parts of the emergent plants are affected by various habitat conditions.Frequent flooding is a typical habitat characteristic of the marsh.It is reseasonable that the decomposition of the emergent plants is affected by inundation.In the salt marsh,the decomposition of the litters may also be affected by salinity,vegetation types,etc.Furthermore,the microbes also play an important role in the decomposition of the litters.We set up fixed sampling sites in the beach of Jinze Reservoir and the tidal marshes around the Chongming Island in Shanghai City.Phragmites australis,Typha angustifolia,Canna indica and Cyperus alternifolius growing in the reservoir,and P.australis and Spartina alterniflora growing in the tidal marsh of the Chongming Island were employed to do the experiments.We aimed to investigate the decomposition characteristics of the litters and also the corresponding influencing factors,as well as the composition and diversity characteristics of bacterial communities on the surface of the litters,and their effects on the decomposition of the litters.The main findings were listed below:1.Characteristics and influencing factors of the litter decomposition under the different habitat conditionsThere were obvious differences in the decomposition characteristics and C,N and P contents of the different plant litters between flooded and unflooded conditions.The rate of litter decomposition in the flooded condition was significantly higher than that in the unflooded condition(P<0.05).The decomposition rate of the P.australis leaves was higher than that of the stems(P<0.05),but there was no significant difference in the decomposition rates between the stems and the leaves of C.indica and C.alternifoliu(P>0.05).The C content was generally lower in the flooded condition than in the unflooded condition,but the N content was contrary,and there was no significant difference in P contents between the two conditions(P>0.05).The effects of salinity on the litter decomposition varied with plant species,and C,N and P contents in the litters were different under the different salinity conditions.The decomposition rates of P.australis stems at low salinity was 2.2-3.0 times that of those at high salinity.The decomposition rates of the P.australis leaves was 1.2-1.4 times that of those at high salinity.However,the decomposition rates of the S.alterniflora litters had no significant difference at the different salinities(P>0.05).There was no significant difference in C contents in the P.australis leaves at the different salinities(P>0.05),while the N,P content of the P.australis leaves at high salinity was significantly lower than that at low salinity(P<0.05).The C content of the S.alterniflora leaves at high salinity was significantly higher than that at low salinity(P<0.05),while N content was significantly lower than that at low salinity(P<0.05).There was no significant difference in P contents at the different salinities(P>0.05).And the difference of the element release characteristics of the stem litters at the different salinities also appeared to be not significant(P>0.05).The effects of vegetation habitats on the litter decomposition varied with plant species,and the decomposition of litters of the different plants and organs was affected by the different litter quality factors.In the S.alterniflora habitat,the annual decomposition rates of the stems and the leaves of S.alterniflora were about 2.3 and1.2 times those of the P.australis litters,but in the P.australis habitat,the difference of decomposition rates of S.alterniflora and P.australis was not significant(P>0.05).In the P.australis habitat and the S.alterniflora habitat,the C content of P.australis was generally higher than that of S.alterniflora,while the difference in N contents between the two species was not significant(P>0.05).The P content in the P.australis leaves was significantly lower than that in the S.alterniflora leaves(P<0.05).There was no significant difference in C/N and N/P of the P.australis litters and the S.alterniflora litters(P>0.05).The decomposition rate of the P.australis stem litters was significantly correlated with C,N,P contents,N/P and initial N contents of the litters(P<0.01),and the decomposition rate of the leaf litters was significantly correlated with C contents,C/N,N/P and initial C,N,P contents(P<0.01).The decomposition rates of the stem litters and the leaf litters of S.alterniflora were significantly correlated with N/P and initial P contents of the litters(P<0.01).There were differences in the relationship between these litter quality factors and litter decomposition at the different sites.2.Characteristics and influencing factors of bacterial community composition and diversity on the litter surfaceAt the phylum level,the bacterial community composition on the surfaces of the P.australis litters and the S.alterniflora litters was basically similar,and the relative abundance of some dominant bacterial groups was significantly different in the different seasons.Proteobacteria,Actinobacteria,Firmicutes,Chloroflexi and Bacteroidetes were the main bacterial communities attached to the stem litters and the leaf litters of P.australis and S.alterniflora.The relative abundance of Proteobacteria on the surface of the P.australis leaf litters in spring was significantly higher than that in winter(P<0.05),but the relative abundance of Proteobacteria on the surface of the stem litters had no significant difference among the different seasons.The relative abundance of Firmicutes on the leaf and stem litters of P.australis in spring was significantly higher than that in winter(P<0.05),while the relative abundance of Chloroflexi in spring was significantly lower than that in autumn and winter.The relative abundance of Firmicutes on the stem and leaf surfaces of S.alterniflora in spring was significantly higher than that in summer,autumn and winter(P<0.05),while the relative abundance of Actinobacteria and Chloroflexi was significantly lower than that in summer,autumn and winter(P<0.05).Seasonal variation,litter quality and geographical location had significant effects on the composition and diversity of the bacterial communities,while there was no significant difference in bacterial community diversity on the litter surfaces of the different plant species(P>0.05).The diversity characteristics of the bacterial communities attached to the P.australis litters and the S.alterniflora litters varied with the seasons.The bacterial community diversity in spring was significantly lower than that in summer,autumn and winter(P<0.05).The richness and evenness of bacterial communities in winter were significantly higher than those in spring(P<0.05).In spring,autumn and winter,there was no significant difference in bacterial community diversity among the different sites(P>0.05),but it appeared in summer(P<0.05).The diversity of bacterial communities attached to th leaf litters of P.australis and S.alterniflora was greatly affected by C content,N content and N/P.The composition of bacterial community on the litter surface was affected by the litter quality,while at the same time,the variation of the bacterial community composition had a certain effect on the litter quality,thus affected the decomposition rate of the litters.In summary,inundation promotes the decomposition of emergent plant litters in the marsh,but the higher the salinity,the less conducive to the decomposition of litters.The decomposition characteristics of the different plant litters are different,and the composition and diversity of bacterial communities on the surface of the litters are also different at the different decomposition stages.In future studies,a variety of environmental factors should be combined to comprehensively explore the effects of the habitat conditions on the litter decomposition and also the composition of bacterial communities on the surface in the marshes. |
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