| The Loess Hilly-gully region is the most serious soil erosion area on the Loess Plateau, and is the major sediment source place of the Yellow River. Vegetation is the key factor to control soil and water loss and recover eco-environment. Since the implementation of the “Grain for Green” project at 1999, the vegetation coverage has increased obviously, and the soil and water loss has decreased also. Therefore, in the present study, the Loess hilly-gully region in Shaanxi province was selected as the research object, soil physical and chemical properties, microbial biomass and the characteristics of bacterial and fungi were studied. Different vegetation zones, including forest vegetation zone, brush-grass vegetation zone, grass vegetation zone, sandy ecozne and desert ecozone were choosen as the research area in the Gully region of Loess Plateau. The main results as followed:(1) Vegetation types significantly altered soil properties. Soil p H and soli bulk density(BD) varied from 7.93 to 8.36 and from 0.95 to 1.66 g/cm3. Soil p H and BD in the forest ecosystem were the lowest and highest in the desert ecosystem. The soil organic matter(SOM) contents of the soils differed from vegetation types. The forest ecosystem were significantly higher than the other ecosystems. The total nitrogen(TN) content in the forest ecosystem was the highest and lowest in the sandy ecosystem, and total phosphorus(TP) content in the forest and forest-grass ecosystem was highest and lowest in the sandy ecosystem. The ratio of C/N in the desert ecosystem was significant higher than that in grass and forest ecosystem, and the ratio of N/P in the forest and forest-grass ecosystems was significant higher than that in other ecosystems. MBC ranged from 519.71 mg/kg in forest ecosystem, to 20.18 mg/kg in sandy ecosystem, and it did consistently decrease across the latitude gradient. Overall, Forest ecosystem had the highest level of nutrients while sandy and desert ecosystem had the lowest. In all, from south to north, along the increasing latitude gradient, soil p H and BD increased, and SM, SOM, TN, TP, NN, AN, AP, AK and MBC decreased.(2) The element stoichiometry has been successfully used in indicating community succession and vegetation restoration in recent years. Information about the effects of different latitudes on soil C, N, and P stoichiometry can help to understand the relationships of vegetation restoration and soil quality, and it is also beneficial to the process and function of ecosystem. However, the effects of latitudes on the soil stoichiometry are poorly documented on the Loess Plateau. To explore the effects of latitudes on ecological stoichiometry of soils in the north of Shaanxi province on the Loess Plateau, 34 soil sample sites were conducted from 5 vegetation zones. Soil organic carbon, total nitrogen, total phosphorus and other properties were analyzed in all soil samples. The results indicated that soil C:N, C:P, N:P ratios varied with latitudes in the range of 8.79~22.00, 9.91~35.92 and 1.06~3.25 in the 0~5 cm soil layer and in range of 8.02~21.03, 7.36~24.01 and 0.82~2.22 in 5~20 cm soil layer, respectively. Soil C:N ratio did not change much with latitudes. Soil C:P ratio and N:P ratio decreased significantly with rising latitudes. Soil organic carbon, total nitrogen and total phosphorus were quite consistent in spatial distribution, showing the same trend of declining with latitude in the studied areas, and they were higher in the 0~5 cm soil layer than those in the 5~20 cm soil layer. There were significant positive correlations between soil organic carbon, total nitrogen and total phosphorus. Both soil C:N ratio and C:P ratio were significantly positively correlated to the soil N:P ratio while the soil C:N ratio was significantly negatively correlated to the soil C:P ratio. Phosphorus was lower in the high latitude areas than that in the low areas. The soil nutrients, such as total nitrogen, phosphorus and soil organic carbon, gradually accumulated along with the vegetation restoration, the contents of these nutrients were significantly higher in forest vegetation than that in desert and sandy vegetation zones. It seemed that the vegetation grown in the soil lies in higher latitude zone is more easily limited by nitrogen than that grown in lower latitude zone.(3) Fifteen soil sample sites collected across a broad geographic latitude across 600 km with five different vegetation types, climate, soil chemical properties in this study, were used to investigate the direct influence of ecosystems on the structure of bacteria. 142444 sequences obtained from 454 pyrosequencing method were divided into 36816 operational taxonomic units(OTUs) based on 97% similarity. Analysis result shows the dominant taxonomic phyla observed in all samples were Actinobacteria, Proteobacteria, Chloroflexi, Acidobacteria and Planctomycetes. Actinobacteria and Proteobacteria was the two most abundant groups in all samples. The proportion of Actinobacteria rised from 14.73% to 40.22% followed with ecosystem changes from forest to sandy. However, the ratio of Proteobacteria revealed an opposite result compared with Actinobacteria, the proportion slipped from 35.35% to 21.40% when ecosystem changes from forest to sandy. Actinobacteria and Proteobacteria had significant correlation with latitude, p H, and soil moisture and nutrients. From south to north, latitude was significantly with correlated with soil chemical and physical properties. Because of that, Actinobacteria and Armatimonadetes, Proteobacteria, Planctomycetes, and Bacteria_unclassified had significant correlation with latitude, suggesting that latitudinal diversity gradient was the key factor to effect soil bacterial community composition. However, along with the latitude gradient, Chloroflexi, Bacteroidetes and Cyanobacteria had a narrow ranges, which doesn’t varied with the soil and environment factors. Latitude, soil moisture, total phosphorus(TP) and the ratio of total organic carbon to total phosphorus(C/P) were the key factors to effect the compositions of soil bacterial on the Loess Plateau of China. In addition, high-throughput 454 pyrosequencing was a suitable method for characterizing microbial communities of soils in the Loess Plateau.(4) Fungi strongly influence the structure and function of the soil ecosystem, playing a key role in many ecological processes including as decomposers, plant mutualists and pathogens. Fungal community structure is affected by the types of vegetation, climate and soil chemical properties as well as other factors. However, we lack a basic understanding of the mechanisms underlying these effects. Five ecozones on the Loess Plateau in China were selected at different latitudes, and pyrosequencing of the ITS(intergenic transcribed spacer) gene region was used to analyze changes in soil fungi diversity and composition. A total of 158244 valid sequences were generated using 454 pyrosequencing. The number of sequences per site ranged from 6049 to 14497, with an average of 10550. At a genetic distance of 3 %, the highest fungal diversity was found in the grass ecozone, whereas the lowest diversity was observed in the forest ecozone. In the grass ecozone, species richness and Shannon’s diversity index were highest, whereas the sandy ecozone had a lower degree of species richness. At the phylum level, the dominant phyla were: Ascomycota, Basidiomycota, Ciliophora, Chytridiomycota and Glomeromycota. In the forest ecozone, the Basidiomycota family was the most abundant, followed by the Ascomycota, whereas in the grass, forest-grass, sandy and desert ecozones, the Ascomycota family was the most abundant. Soil bulk density(BD), microbial biomass carbon(MBC), total phosphorus(TP), total nitrogen(TN), soil organic matter(SOM), and available potassium(AK) significantly influenced the abundance of Ascomycota and Basidiomycota. Ciliophora were significantly positively correlated with latitudes, and significantly negatively correlated with ammonium nitrogen. Soil chemistry properties and latitudes had little influence on the abundance of Chytridiomycota and Glomeromycota. Vegetation restoration is an ecologically efficient practice for the fungal recovery of degraded soil in the Loess Plateau. |
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