OB-20 (JTK0041):

Spatial Distribution and Community Structure of Soil Protists in the Rice Rhizosphere Revealed by a “Mini-rhizobox” Experiment

Rice rhizosphere is a hot spot for microorganisms, in which protists are one of the main microeukaryotic groups. However, less is still known about spatial distribution and community structure of protists in the rice rhizosphere. Here, we made a “mini-rhizobox” experiment in order to explore the micro-scale distribution of protists in the rice rhizosphere at the early plant growth stage. A rice seedling was grown in an agar media that contains nutrient solution and a soil suspension taken from a paddy field. Protists grown in the microcosms were regularly observed under microscope and enumerated with a direct counting method. Different types of protists densely populated the roots and surrounding area with an extended area at the root tip parts. Flagellates were the main protistan group that showed the highest frequency of colonization. Ciliates, flagellates, and amoeba showed different spatial distribution patterns. Flagellates populated the rice roots and the adjacent area, while amoeba populated a little apart from the population area of flagellates. Ciliates were observed mainly in the root tip area. The microeukaryotic community structure in the rice rhizosphere analyzed by PCR-DGGE was distinct from those in the non-rhizosphere of the planted microcosm and in the unplanted microcosm. Protistan species inhabiting the rice rhizosphere were affiliated to flagellates (Nucleocercomonas sp. and Gymnophrys sp.), amoeba (Echinamoeba sp.), and ciliates (Colpoda sp. and Oxytricha sp.) in agreement with the results of microscopic observation. Our results suggested that the rice roots provide a favorable habitat for protistan species with the prominent effect at the tip parts and that amoeba, ciliates, and flagellates may differently respond to the micro-scale environmental gradients in the rhizosphere.

keywords:Protozoa,Rice rhizosphere,DGGE,Microscopic observation,Micro-scale distribution