| Relationship and interaction between soil quality restoration and vegetation rehabilitation are the key factors for vegetation reconstruction and eco-environment sustainable development on the Loess Plateau. Soil microbiological characteristic can reflect the soil quality changes sensitively, also is it very important to soil structure and plant nutrition cycling. Hence, it becomes a focal point to be used as one of soil quality assessment indices. To meet the requirement of eco-environment construction in the Loess Plateau and to explore the hotspot in soil and ecology sciences, responses and evolvements of soil microbial indices in the process of vegetation restoration in Hilly-Gully Loess Plateau were studied systematically in this thesis. Soil samples under the grassland vegetation of different rehabilitation ages and different succession stages of natural recovering as research objects were selected in Hilly-Gully area and Yun-Wu mountain lies in Southern of Ning-xia province. Soil microflora, soil microbial biomass (SMB), soil microbial respiration and several soil enzyme activities were determined by traditional method; and soil microbial community diversity were detected by PLFA method. The evolvement regular pattern of soil microbial properties during the processes of vegetation natural rehabilitation and the influence of different land uses to soil microbial characteristics were found. Which can provide scientific references for vegetation rehabilitation and soil quality care in the Hilly-Gully Loess region, and enrich the theory and method for soil quality management. The results obtained were summarized as follows:(1) The 35 kinds PLFA contents of soil samples under different succession stages of natural recovering vegetation in Yun-Wu mountain were identified by GC-MS, and there has a very close relationship between the content of PLFA and the time of vegetation recovering. The 35 PLFA contents all increased with the increasing of enclosed year in grassland soil, among which, the contents of 10Me16:0, i15:0 and 19:1ω11 increased faster especially; the contents of 16:0,18:1ω9c,18:1ω11 and 16:1ω9 were marked higher than others; the contents of 2OH14:0,3OH14:0 and 2OH16:0 were lower relatively. The contents of the 35 kinds PLFA were all higher in the grassland soil than in agriculture soil clearly. The straight-saturate18:0 was high in agriculture soil, but it decreased relatively with the vegetation time prolong, and it became lower after 23 years enclosure in grassland. Except 10Me16:0 and 10Me17:0, most of PLFA were higher in surface layer (0-10cm) than subsurface layer(10-20cm) soil in grassland. In cultural soil, most of PLFA were no different in two layers, except 18:0 was higher in 0-10cm than 10-20cm. (2) The PLFA contents of total alive microbes, bacteria, fungi, actinomyces increased lineally as the vegetation recovered time increasing. In 0-10cm soil layer, the highest correlation lies between the contents of fungi's PLFA and the vegetation recovering time; while in 10-20cm soil layer, The contents of actinomyces's PLFA had the marked positive relevance with recovering year. The contents of G- bacteria and VAM fungi's PLFA were also increased as the enclosure year prolonged, but G+ bacteria's PLFA content had no clearly correlation with the enclosure years in 0-10cm layer, same phenomenon observed in straight-saturate PLFA. The PLFA contents of total alive microbes, bacteria, fungi, actinomyces, G+ bacteria, G- bacteria and VAM fungi in grassland soil were all higher than agriculture soil.(3) The ratio of PLFA (cy17:0 and cy19:0) to (16:1ω9and 18:1ω11) was higher in agriculture soil than grassland soil. It was higher in 10-20cm than 0-10cm in grassland soil, but it has no change in different vegetation rehabilitation years. The value of this ratio is less than 0.5 in both grassland soil and agriculture soil. The ratio of PLFA (fungi/bacteria) has no change in 0-10cm layer both in grassland soil and agriculture soil, even in different recovering sites. But it increased in 10-20cm layer soil along with the enclosed year extending. The ratio value of PLFA (G+/G-) was higher in agriculture soil than grassland soil.(4) Bacteria was higher in 23 year and 58 years sites in 0-20 cm during the process of vegetation rehabilitation, meanwhile, it is higher in summer soil samples. The increasing rate of Bacteria were11.6% and 59.5% before 23 years rehabilitation in two layers separately. The amount of Bacteria decreased after 23 years rehabilitation. Fungi have the different trend along with the rehabilitation years, which was increased step by step. The amount of Fungi increased faster after 23 years site than before. In 0-10 cm, fungi has three peaks of high amount in 15, 58 and 78 years sites in spring season, but the high peaks of fungi amount were in 9 year and 78 year sites in 20-40cm layer. The amount of Actinomycetes increased before 23 year site then declined after this time.(5) SMB increased in the process of vegetation rehabilitation, meanwhile, it enhanced very fast before 23 year vegetation rehabilitation then almost keep stable. Especially the changes of A280 and soil microbial biomass carbon (SMBC) can reflected the soil quality sensitively. SMB declined very fast after the grassland cultured, in which the value of⊿ A280 changed most quickly, then SMBC and soil microbial biomass nitrogen (SMBN) followed.(6) The soil basal respiration increased as the logarithm function with the vegetation recovery time extending, but the soil respiratory quotient( qCO2) decreased as the logarithm function with the vegetation recovery time extending. Soil respiratory quotient( qCO2) of fresh soil was lower than air-dried soil. Grazing reduced grassland soil basal respiration, but has no influence to qCO2. Controversially, reclamation increased qCO2 obviously. The air-dried soil can be used to measure the soil basal respiration after pre-incubation, and it can reflect the quality of soil microbial activity more stable. The cumulative respiration (CR) is more direct and clear in reflecting soil microbial activity of different soil than equivalent daily respiration (EDR).(7) The activity of soil invertase, urease, alkaline phosphatase and dehydrogenase were all increase along with the vegetation rehabilitation ages. These enzymes activity responses can be divided into two stages, they increased very quickly before enclosed 23 years and became slower after 23 years. The increasing rate in surface layer of these four enzyme activities is much higher than subsurface layer. Soil catalase activity has no obvious change regular pattern. There has clearly positive correlation among activities of soil invertase, urease, and alkaline phosphatase. Compared to enclosed land, the activity of soil dehydrogenase invertase, alkaline phosphatase and urease decreased 35.7%,56.1%,60.8% and 81.5% in 0-20cm layer after reclamation, also decreased 31.5%,32.9%,51.7% and 79.8% in 20-40cm layer.(8) Two techniques were compared that uses the UV absorbance at 280nm of 0.5M K2SO4 extracts of fumigated and unfumigated soils and fumigation-waterlogged incubation to estimate the concentrations of SMBN. The results showed that the pre-incubation days of air-dried soil to measure SMBN should be 10 days. The result of SMB using the UV absorbance at 280nm in fresh soil was bigger than from air-dried soil, but both results had same regular changing, which showed that air-dried soil can be used to measure SMB. Considering the measured accuracy,The 280nm UV absorbance technique has the advantages as followed, simple steps, less error, less time needed and better repeatability than fumigation/ waterlogged incubation method. So it can be used as the measure method of SMBN.
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