STUDIES ON THE RHIZOSPHERE OF PADDY RICE .6. EFFECTS OF ANAEROBIOSIS ON MICROBES

In the previous paper, it was supposed that the abnormally low RIS ratios about aerobic and facultatively anaerobic microbes with paddy rice growing in the submerged condition might come from the detrimental effects of reduced condition, which might suppress the growth of these microorganisms in the substrate-rich rhizosphere. To examine this supposition, the effects of roots of paddy rice on anaerobic microbes were studied. At the flowering stage, RIS ratios for anaerobic microbes, anaerobic dye-tolerant microbes, and sulfate reducing microbes showed more than 50. The low RIS ratios for aerobic and facultative anaerobic microbes in the rhizosphere of paddy rice might come not from the accumulation of ferrous iron, but from the accumulation of other toxic substances. The results also showed that in some submerged soil a little high RIS ratios could be expected for the aerobic and facultative anaerobic microbes, where the condition may be permitted enough to decrease the Eh in the non-rhizosphere soil as low as in the rhizosphere, because of the relatively hiah resistanceS of aerobic and facultative anaerobic microbes in the rhizosphere to the very low Eh value compared with the microbes in the non-rhizosphere. © 1979 Taylor & Francis Group, LLC.