[Ecological distribution and antimicrobial effects of soil actinomycetes in artificial vegetation systems in Shazhuyu of Qinghai, China].

In order to probe into the effects of artificial vegetation rehabilitation on soil actinomycetes, dilution plate and agar block methods were used to investigate the ecological distribution and antimicrobial effects of actinomycetes in sandy soil in Shazhuyu area of Qinghai after artificial vegetation restoration. The results showed that with the vegetation rehabilitation and the improvement of vegetation coverage on alpine sandy dry land, the quantity of soil actinomycetes increased significantly, being 145.4% higher in the grassland transferred from farmland than in sandy land. The quantity of soil Micromonospora in grassland transferred from farmland was about six times as much as that in sandy land. The average selection rate of antimicrobial actinomycetes was increased greatly, with the antimicrobial actinomycetes in the soil of grassland transferred from farmland, the antibacterial actinomycetes in the soil of natural grassland, and the pathogenic fungus resistant aetinomycetes in the soil of forestland being approximately 2, 3.2 and 1.5 times as much as those in the soil of sandy land, respectively. Vegetation coverage and soil nutrients had great influences on the quantities of actinomycetes and antimicrobial actinomycetes. The contents of soil organic matter and alkali-hydrolyzable nitrogen and the yield of fresh grasses had significant correlations with the quantities of actinomycetes (P < 0.01), and the content of soil organic matter and the yield of fresh grasses significantly correlated with the strain numbers of antimicrobial actinomycetes (P < 0.01). Furthermore, vegetation coverage and the contents of soil total nitrogen, total phosphorous, total potassium, total salt, and available potassium had significant correlations with the total quantities of actinomycetes, Streptomycetes, and Micromonospora (P < 0.05).

[Effects of microwave irradiation on isolation of soil actinomycetes].

Dilution plate- and agar block methods were employed to study the effects of microwave irradiation on the isolation of soil actinomycetes. The results showed that: 1) Microwave irradiation could significantly increase the total quantity of isolated actinomycetes. With the increasing duration of microwave irradiation, the total quantity of actinomycetes in soils with high organic matter content tended to increase first and decrease then. This quantity on GA and HA culture medium increased by 8.3%-92.6% and 24.4%-108.5% when the irradiation lasted 3-15 minutes, but decreased by 62.1%-78.8% and 41.4%-79.8%, respectively when the irradiation lasted 18-24 minutes, in comparison with that on the control medium. Microwave irradiation showed no remarkable effects on the total quantity of actinomycetes in the soils with low organic matter content. 2) Microwave irradiation also exerted remarkable effects on the number of actinomycetes species. With the increase of irradiation duration, the actinomycetes species number in soils with high organic matter content appeared to increase first and decrease then. When the irradiation lasted 3-24 minutes, the newly identified actinomycetes species on GA and HA culture medium, which included rare actinomycete genera such as Promicromonospora and Streptoverticillium, took up 62.5%-85.7% and 66.7%-83.3% of all the actinomycetes species respectively, and the genus Streptmycete also had obvious variation. Soils with low organic matter content showed the similar tendency. 3) Microwave irradiation could exert remarkable effects on the percentages of antimicrobial actinomycetes strains to all test actinomycete strains. When the microwave irradiation lasted 6, 9, and 15 minutes, the percentages of antimicrobial antinomycetes strains on the culture mediums increased by 66.7%, 66.7%, and 83.3%, and the newly identified antimicrobial antinomycetes strains made up 70.0%, 90.0%, and 81.8% of all the antimicrobial antinomycetes strains, respectively.

[Nutrient contents and microbial populations of aeolian sandy soil in Sanjiangyuan region of Qinghai Province].

Sanjiangyuan region (the headstream of three rivers) in Qinghai Province of China is the highest and largest inland alpine wetland in the world. The study on the nutrient contents and microbial populations of aeolian sandy soils in this region showed that soil organic matter content increased with the evolution of aeolian sand dunes from un-stabilized to stabilized state, being 5.9 and 3.8 times higher in stabilized sand dune than in mobile and semi-stabilized sand dunes, respectively. Soil nitrogen and phosphorus contents increased in line with the amount of organic matter, while potassium content and pH value varied slightly. The microbial populations changed markedly with the development of vegetation, fixing of mobile sand, and increase of soil nutrients. The quantities of soil bacteria, fungi and actinomycetes were 4.0 and 2.8 times, 19.6 and 6.3 times, and 12.4 and 2.6 times higher in stabilized and semi-stabilized sand dunes than in mobile sand dune, respectively, indicating that soil microbial bio-diversity was increased with the evolution of aeolian sand dunes from mobile to stabilized state. In addition, the quantities of soil microbes were closely correlated with the contents of soil organic matter, total nitrogen, and available nitrogen and phosphorus, but not correlated with soil total phosphorus, total and available potassium, or pH value.