Effects Of Freshwater Input On Soil Microbes And Aggregate Composition In The Yellow River Estuarine Wetlands

Severely degraded wetlands due to the lack of freshwater were restored by reintroducing freshwater through the placement of artificial dikes and channels in the Yellow River estuarine wetlands of China.Many studies had evaluated the performances of this restoration project in aspects of vegetation,soils,hydrology,wildlife,etc.In contrast,limited information was available on the effects of restoration project on soil microbes and aggregate composition.In this study,differences in soil microbial biomass,community composition and soil aggregate composition were assessed to study the effects of freshwater input and different freshwater input strategies on soil microbes and soil structure,which would contribute to the understanding of wetland restoration.Chloroform fumigation-extraction(CFE)method and phospholipid fatty acid(PLFA)analysis were used to characterize soil microbial biomass and community composition.Wet-sieving method was used to separate different soil aggregate size classes.The results showed significantly elevated microbial biomass in wetland soils with freshwater input.Restored wetlands with freshwater input all the year(RA)supported a significantly higher microbial biomass than that in wetlands with freshwater input once a year(R1)and stopped(RS).Significantly higher fungal abundance were observed in restored P.australis covered wetlands,compared with unrestored wetlands,which might contribute to a greater proportion of macroaggregates in the soil.Total carbon and nitrogen concentrations in the macroaggregates were both promoted in soils with freshwater input,which potentially favored soil microbes to colonize.With the freshwater input strategies changed from RA to RS,the proportion of large macroaggregates was significantly increased,meanwhile,fungal abundance were decreased in contrast to actinomycete abundance.Actinomycete possibly played an important role in the formation of large macroaggregates in place of fungi.Total carbon and nitrogen concentrations in the small macroaggregates increased in the order:RA>R1>RS.Carbon and nitrogen mineralization in each class of soil aggregates were significantly higher in RA than those in R1 and RS.As the proportion of large macroaggregates increased,soil carbon and nitrogen stocks in them were promoted.