Microscopic observation of the decomposition process of leaf blade of rice straw and colonizing microorganisms in a Japanese paddy field soil during the cultivation period of paddy rice

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Leaf blades of rice straw were placed in the plow layer of a Japanese paddy field at the time of transplanting, they were sampled periodically for the observation of the decomposition process with a scanning electron microscope. Apparent decomposition of the leaf blade started from 19 d after the placement in the field. It was faster than that of the leaf sheath. But marked decomposition of the epidermal layers by bacteria was observed around the colonies only in the late period of rice cultivation. It was suggested that the platelet-like epicuticular wax on the surface of the leaf blade prevented the decomposition of the leaf blade by restricting direct contact of surface colonizers on epidermal layers. On the contrary, abundant bacteria were found inside the tissues of the leaf blade before its placement in the field. They developed densely in the tissues within a short period of time after the placement. From these observations, it was concluded that the leaf blade is decomposed mainly from inside the tissues.