Responses of soil inhabiting nitrogen-cycling microbial communities to wetland degradation on the Zoige Plateau,China

The wetlands on the Zoige Plateau have experienced serious degradation,with most of the original marsh being converted to marsh meadow or meadow.Based on the 3 wetland degradation stages,we determined the effects of wetland degradation on the structure and relative abundance of nitrogencycling(nitrogen-fixing,ammonia-oxidizing,and denitrifying) microbial communities in 3 soil types(intact wetland:marsh soil;early degrading wetland:marsh meadow soil;and degraded wetland:meadow soil) using 454-pyrosequencing.The structure and relative abundance of nitrogen-cycling microbial communities differed in the 3 soil types.Proteobacteria was the predominant phylum in most soil samples but the most abundant soil nitrogenfixing and denitrifying microbial bacteria differed at the class,order,family,and genus levels among the 3soil types.At the genus level,the majority of nitrogenfixing bacterium sequences related to Bradyrhizobium were from marsh and marsh meadow soils;whereas those related to Geobacter originated from meadow soil.The majority of ammonia-oxidizing bacterium sequences related to Nitrosospira were from marsh(except for the 40-60 cm layer),marsh meadow and meadow soils;whereas those related to Candidatus Solibacter originated from 40-60 cm layer of marsh soil.The majority of denitrifying bacterium sequences related to Candidatus Solibacter and Anaeromyxobacter were from marsh and meadow soils;whereas those related to Herbaspirillum originated from meadow soil.The distribution of operational taxonomic units(OTUs)and species were correlated with soil type based upon Venn and Principal Coordinates Analysis(PCoA).Changes in soil type,caused by different water regimes were the most important factors influencing compositional changes in the nitrogen-fixing,ammonia-oxidizing,and denitrifying microbial communities.

Effects of Wetland Utilization Change on Spatial Distribution of Soil Nematodes in Heihe River Basin, Northwest China

The first account of the effects of wetland reclamation on soil nematode assemblages were provided, three sites in Heihe River Basin of Northwest China, that is grass wetland(GW), Tamarix chinensis wetland(TW) and crop wetland(CW) treatments, were compared. Results showed that the majority of soil nematodes were presented in the 0–20 cm soil layers in CW treatments, followed by in the 20–40 cm and 40–60 cm layers in GW treatments. Plant-feeding nametodes were the most abundant trophic groups in each treatment, where GW(91.0%) > TW(88.1%) > CW(53.5%). Generic richness(GR) was lower in the TW(16) than that in GW(23) and CW(25). The combination of enrichment index(EI) and structure index(SI) showed that the soil food web in GW was more structured, and those in TW was stressed, while the enrichment soil food web was presented in the CW treatment. Several ecological indices which reflected soil community structure, diversity, Shannon-Weaver diversity(H′), Evenness(J′), Richness(GR) and modified maturity index(MMI) were found to be effective for assessing the response of soil namatode communities to soil of saline wetland reclamation. Furthermore, saline wetland reclamation also exerted great influence on the soil physical and chemical properties(p H, Electric conductivity(EC), Total organic carbon(TOC), Total nitrogen(Total-N) and Nitrate Nitrogen(N-NO3–)). These results indicated that the wetland reclamation had significantly effects on soil nematode community structure and soil properties in this study.