تاثير ماده آلي و گوگرد بر جمعيت ميكرو ارگانيسم هاي اكسيد كننده گوگرد در خاك 2- جمعيت هتروتروف هاي اسيد دوست و خنثي دوست اكسيد كننده گوگرد

The Effects of Organic Matter and Elemental Sulfur on the Population Levels of Sulfur Oxidizing Microorganisms in Soil 2. The Population of Acidophilic and Neutrophilic Sulfur Oxidizing Heterotrophs

Sulfur is one of the essential elements needed for plant growth and development. In addition, it has been used for disease control as well as for pH reduction in alkaline soils. The chemical oxidation of sulfur in soils is generally very slow. Microbial activity of some microorganisms in soils could enhance the process of oxidation of sulfur, which evantually results in pH decline. A variety ranges of heterotrophic microorganisms play role in sulfur oxidation, but their role is unclear in the different ecosystems and it is possible that the role of heterotrophic species, could be more important than chemolithotrophic ones in some special cases. Heterotrophic microorganisms with growth in different pH, range are classified into two groups of: acidophilic and neutrophilic.The objective of this study was to investigate the effect of organic matter and sulfur on the population of sulfur oxidizing heterotrophic microorganisms. Two soil samples containing acidophilic and neutrophilic heterotroph microorganisms, with a high pH along with different sulfate and CaC03 contents, were selected. The following four treatments were tested: time in days following the start of the experiment {0(T1), 10(T2), 20(T3), 40(T4) and 80(T5)}, soil {Takestan(Sl) and Ajabshir(S2)}, organic matter {O(Ol) and 1.5%(02)} and sulfur rates {0(G1) and 0.2%(G2)}. At five stages of the experiment, samples were taken from pots for chemical and biological analysis (pH, EC, sulfate and the population of microorganisms). The results indicated that the population of acidophilic and neutrophilic heterotrophs was on the increase till 20th day, decreasing afterwards. Simple and interactional effects of all factors on soil sulfur oxidizing microorganisms reactionary soilxO.M, and O.M.xS on heterotrophic acidophylic microorganisms by the simple effect of soil and the interactionary effect of O. M. xS on the population of heterotrophic neutrophylic S oxidizing microorganisms. An application of 1.5% O. M. increased the population of heterotrophic acidophylic and neutrophylic microorganisms by 166 and 265 percent respectively. An application of S too increased the population of the two groups by 20, 39%. There exists a close relationship between the population of S oxidizing microorganisms (heterotrophic acidophylic and neutrophilic) and soil pH. With an increase in pH their population decreases. Variation in population of 38 and 49 percent respectively is explainable with regard to soil pH.