MICROBIAL COLONIZATION AND DECOMPOSITION PROCESSES IN RICE RHIZOPLANE .2. DECOMPOSITION OF YOUNG AND OLD ROOTS

Microbial colonization of the rice roots and their decomposition processes were investigated with emphasis placed on the young roots with mucigel and root hairs and on the old roots with ferric hydroxide-covering. The results obtained are as follows: A. Young roots. 1. The mucigel was commonly observed on young roots with many root hairs, where microorganisms and soil particles were present side by side. These microorganisms appeared to decompose actively the mucigel though they did not attack epidermal cells. 2. The epidermal cells were mainly decomposed from inside by the microorganisms which invaded the epidermal layer through damaged root hairs. 3. The boundary between neighboring epidermal cells became loose when the cells aged, which allowed for microbial invasion of the epidermal layer. 4. Microbial colonization spread longitudinally along roots, neighboring cells of the severely invaded cells being spared from microbial invasion. 5. The shape of the microorganisms in a particular colonized cell of the epidermal and exodermal layers was very similar, though the shape of the microorganisms in the cells of these layers varied widely. 6. Ferric hydroxide deposition was observed either on the cells which were colonized by the microorganisms or at boundaries between cells. The ferric hydroxide deposition appeared to suppress further microbial colonization. B. Old roots. 1. Ferric hydroxide cover suppressed the microbial decomposition of rice roots. 2. The colonizing microorganisms extended their territories in all directions in the epidermal and exodermal layers. 3. Many kinds of microorganisms and soil particles were present inside a given cell of the epidermal and exodermal layers. © 1990 Taylor & Francis Group, LLC.