盐度对稀释平板法研究红树林区土壤微生物数量的影响

在使用稀释平板法分离潮间带红树林及其对照光滩土壤微生物以及计数时,多数情况下使用陈海水制作培养基和稀释水,很少考虑培养基和稀释水的盐度对最终计数结果的影响.使用稀释平板法研究了盐度对福建九龙江口红树林区与深圳福田红树林保护区土壤微生物平板计数的影响,结果表明培养基与稀释水盐度对微生物数量有明显的影响.统计分析显示细菌的海水稀释效果优于淡水,而放线菌与真菌则刚好相反(P<0.05,一个例外).海水不适合配制红树林区土壤微生物平板计数的培养基,从0～35,高盐度的平板培养基会降低微生物的数量,尤其是放线菌的数量,尽管培养基的盐度对真菌影响无规律,但细菌数量在低盐度时比在高盐度和不加氯化钠时要多.根据盐度效应,提出了稀释平板技术应用于潮间带的红树林及其相应光滩时的优化方法,认为细菌应该用海水作无菌稀释水,而放线菌和真菌则应用淡水作稀释水;包括光滩在内的红树林区土壤微生物分离与计数的培养基宜控制较低盐度范围.

Effect of salinity on microbial densities of soil in the dilution plate technique applied in mangrove areas

When the soil microbial densities are determined in mangroves and corresponding mudflat at the same tidal level by the dilution plate method, the agar media and dilution water are generally made up of aged seawater in most cases, and effects of salinity in agar media and dilution water on the enumeration of microbes is seldom taken into consideration. The effects of salinity on soil microbial counting from the samples in mangrove areas in Jiulongjiang Estuary of Fujian, and Futian Mangrove Nature Reserve of Shenzhen, China, were tested by dilution plate technique. The results showed that the soil microbial densities in mangroves and mudflat were significantly influenced by the salinity of dilution water and agar media. For the bacteria, the seawater served as sterilized dilution water was significantly (P<0.05) more benefic to the enumeration on the plates than the freshwater, but in reverse for the actinomycetes and fungi. The increasing salinity of media within 35 significantly decreased microbial colonies on the plates, especially for the actinomycetes, in spite of the fact that the effect of salinity of media on fungal numbers was not indefinite. The bacterial colonies were more abundant on the agar plates with low salinity than with high salinity or without any NaCl. It was proposed that some methodological improvements were needed when the dilution plate technique was applied to microbial counting in the samples of mangrove forest and mudflat at the same tidal level in inter-tidal zone. The sterilized dilution water should be prepared with seawater for the bacteria, but with freshwater or low saline water for the actinomycetes and fungi. The salinity of agar media should be low for the microbial isolation and enumeration of soil samples from the mangrove areas including mudflats.