Studies On Ecological Effects Of Secondary Salinization On Facility Culturing Soil And Bioremediation

Facility agriculture has played a huge role in vegetables and other important economic crop cultivation in our country,and won great profit in both economic and social aspect.But large amount of mineral fertilizer used,especially nitrogen,has made soil secondary salinization more serious,and have attracted much attention in recent decades.It is very,important to investigate secondary salinization of soil pollution.In this paper,the effects of secondary salinization on soil microorganism were studied by using greenhouse soil.Moreover,the bioremediation of the pollution of nitrate was also investigated.The main results are showed as follows:1,With the increase of facility cultivation time,organic matter of top soil(0～5cm) did not change obviously;but soil nitrate and total salt were gradually accumulating with the time.The amount of nitrate in 15-year land with 93.16mg/kg is 14.6 times than that in 0-year,and the electric conductivity(EC) is similar.A lower pH were measured after 5-year facility culturing activity.Secondary salinization effects on deep soil(15～20cm) was not as significant as top.2,The effects of different secondary salinization on soil urease,phosphatase and soil respiration were studied by using greenhouse soil.The results showed that the more serious of soil secondary salinization,the more significant of inhibition of soil enzyme and soil respiration.In addition,urease activity of top soil samples compared to 0-year reached extremely significant.3,The number changes of bacteria,fungi and actinomycete in top and deep of every soil samples were studied by the traditional plate count of cultivation,and the relevance of the number of microorganism and the extend of secondary salinization were analyzed.The results showed that the secondary salinization inhibited microorganism growth of top soil,but not deep.EC,the total salt and nitrate was extremely negatively correlated with bacteria and actinomycete,and negatively correlated with fungi.4,The genotoxicity of microorganism in soil contaminated with secondary salinization was studied by the polymerase chain reaction-denaturing gradient gel electrophoresis(PCR-DGGE).From the analysis of DGGE band,it could be concluded that bacteria population has declined and the community structure has changed with increase of secondary salinization.5,A nitrate-transforming bacterium(designated strain NCT-1) was isolated from serious secondary salinization soil collected from greenhouse.The isolated NCT-1 was identified as klebsiella according to its physiological characteristics and 16s rDNA amplification and sequencing analysis.6,The transformation rate of nitrate by NCT-1 bacterium is heavily affected by carbon-nitrogen ratio,incubation pH and incubation temperature.The result is shown that the best incubation condition was 5:1 of carbon-nitrogen ratio,pH 7.0 and 30℃.The transformation rate was about 80%within 72 hours under the best incubation conditions.