| The characteristic of vegetation and the spatial distribution and seasonal changing ofmicrobial number of3main soil microorganism and the physiological bacteria groups ofnitrogen were determined，utilizing the methods of plate colony counting and dilutedculture. The result shows as follow:1.The characteristic of vegetation under different disturbed habitatsIn2types of artificial grasslands habitats (annual and mixed perennial grassland), thecomprising of plant species was relatively simple, the height of plant community wascomparatively high, the change of coverage was obvious, the up-ground biomass was quitebig. In natural grassland, the rodent hill and unfenced grassland, the comprising of plantspecies was simple too, the height of plant community was the lowest in5habitats, thecoverage and the up-ground biomass was small; but in fenced grassland, the comprising ofplant species was abundant, the height of plant community was comparatively high, thecoverage and the up-ground biomass was relatively big. From June to August, theincreasing range of height was comparatively big, but from August to October the rangewas small. Compared with30years ago (1982), the moisture content of soil, the plantcovrage and the grass production have been declining continuously in natural grassland,that is to say that the natural grassland is degenerating.2The spatial distribution and seasonal changing of3main soil microorganism indifferent disturbed habitats(1) In different soil layers, the spatial distribution of microbial number of3main soilmicroorganism in5different disturbed habitats possessed distinct regulation of verticalvariation. In all habitats, the microbial number in0-20cm layer was more than20-40cmlayer by1-4times.(2) In different seasons, the dynamic of microbial number’s alteration was varied. Inall habitats, the microbial number of3main soil microorganism showed evident seasonaltrends in0-20cm layer, which was that the number was quite big in April, then increasedgradually in June, reached the maximum in August, then turned down in October; but thethe trends of seasonal changing was not evident in20-40cm layer. (3) In different habitats，the total microbial number of3main soil microorganism hadremarkable discrimination in different habitats: annual artificial grassland> perennialartificial grassland> fenced natural grassland> rodent hill grassland> unfenced naturalgrassland, and their number range was in5.18×10~6-11.17×10~6cfu/g. The number ofbacteria was the biggest in3main soil microorganism, which occupied47.94-65.46%insum; then the second was actinomycetes, which occupied34.19-51.49%in sum; thesmallest was fungi, which occupied0.35-0.70%in sum. The addition of microbial numberof bacteria and actinomycetes was more than99%of sum.(4) The microbial number’s distribution of3soil microorganism was not alike indifferent disturbed habitats. For fungi, the habitats ranked in order of microbial number as:fenced natural grassland> annual artificial grassland> perennial artifical grassland>rodent hill grassland> unfenced natural grassland; for bacteria: annual artificial grassland>fenced natural grassland> perennial artifical grassland> rodent hill grassland> unfencednatural grassland; for actinomycetes: annual artificial grassland> perennial artificalgrassland> fenced natural grassland> rodent hill grassland> unfenced natural grassland.(5) As time passed by and the degeneration of grassland aggravated, the numberalteration of3main soil microorganism was different. The fungi number of2types ofnatural grasslands presented the trend of decreasing firstly and then turned increasing; butthe trend of decreasing appeared in bacteria and actinomycetes of natural grasslands.3The spatial distribution and seasonal changing of the physiological bacteria groupsof nitrogen in different disturbed habitats(1) In the same habitat, the microbial number of the physiological bacteria groups ofnitrogen (nitrifying bacteria, denitrifying bacteria, the aerobic and anaerobic nitrogen-fixingbacteria) varied greatly in different soil layers. In all habitats, the microbial number in0-20cm layer was more than20-40cm layer by1-5times. In different habitats, themicrobial number varied greatly in same soil layer.(2) In different seasons, the dynamic of microbial number’s alteration was changeable.In all habitats, the number of the physiololgical bacteria groups of nitrogen expressedevident seasonal trends in0-20cm layer, which was that the number was quite big in April,then increased gradually in June, reached the maximum in August, then turned down inOctober; but the trends of seasonal changing was not evident in20-40cm layer. (3) The microbial number’s distribution of the physiololgical bacteria groups ofnitrogen was not alike in different disturbed habitats. For the aerobic nitrogen-fixingbacteria, the habitats ranked in order of microbial number as: rodent hill grassland> fencednatural grassland> annual artificial grassland> perennial artifical grassland> unfencednatural grassland; for the anaerobic nitrogen-fixing bacteria: fenced natural grassland>perennial artifical grassland> annual artificial grassland> rodent hill grassland> unfencednatural grassland; for nitrifying bacteria: fenced natural grassland> annual artificialgrassland> perennial artifical grassland> rodent hill grassland> unfenced naturalgrassland; for denitrifying bacteria: perennial artifical grassland> annual artificalgrassland> rodent hill grassland> fenced natural grassland> unfenced natural grassland.(4) In comparison to30years ago, in2types of natural grasslands, the microbialnumber’s changing was different: the aerobic nitrogen-fixing bacteria displayed the trendsof decreasing firstly and then increasing; nitrifying bacteria showed the identical trends; butfor the anaerobic nitrogen-fixing bacteria and denitrifying bacteria, the trends truned outincreasing continuously;... |
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