Microbial Ecology in Submerged Soils as Revealed by Using TTC (Triphenyl Tetrazolium Chloride), Part 1 : An observation Approach

Abstract

Microorganisms associating with decomposition of rice straw and sesbania leaf in the submerged three Thai paddy soils (one sandy soil and two clayey soils) were examined under a micro-scope. The soils were added with water-soluble colorless TTC which was converted into water-insoluble red formazan when it was reduced by emzyme dehydrogenases of microorganisms so that the micro-habitats favorable for active microorganisms and some of the microorganisms themselves were easily recognized. In addition, sulfate reduction and methane formation could be also followed by observing blackened parts of the plant debris and the appearance of methane bubbles, respectively. Colonization of microorganisms on the plant debris started at cut ends, incisions and then extended to inside of plant debris. Decomposition pattern of rice straw was similar among three Thai soils, though its decomposition rate was somewhat lower for the sandy soil than that for the clayey soils. Decomposition of sesbania leaf was more different between the sandy soil and the clayey soils. A lag period in decomposition of sesbania leaf was recognized in the sandy soil but not in the clayey soils. The decomposition rate was clearly lower for the sandy soil than for the clayey soils. In the sandy soil, the number of protozoa were much less populated near sesbania leaf than near rice straw, though in clayey soils such facts were hardly found. Probably, some organic compounds contained in the sesbania leaf might inhibit the growth of protozoa, this effect being unclear in the clayey soils probably because these organic compounds were adsorbed by clay particles.