Allantoin-induced changes of microbial diversity and community in rice soil

Rice (Oryza sativa L.) may release allantoin into paddy soil. Currently, little attention has been paid to the effects of allantoin on soil microbial diversity and community. In this study, the diversity indices for the microbial community in rice soil and the allantoin-induced shifts in the microbial community composition across moisture regimes versus incubation times were examined by looking at phospholipid fatty acid (PLFA) profiles and PCR-denaturing gradient gel electrophoresis (DGGE) patterns. The total PLFA concentration increased with the amount of allantoin applied during incubation. A similar trend occurred for microbial biomass carbon (MBC) and pH. Furthermore, applying allantoin resulted in an increased ratio of anaerobe: aerobe and bacteria: fungi but decreased the ratio of Gram-negative bacteria: Gram-positive bacteria (GN: GP) and fungal marker 18:2 omega 6,9c under flooded rice soil. A stepwise discriminant analysis of the PLFA pattern clearly separated allantoin-treated samples from non-treated samples. There was also a clear split between different incubation times. Moisture treatments differed in the ratios of anaerobe: aerobe and GN: GP but showed similar trends in total PLFA concentrations and the bacteria: fungi ratio during incubation. These results suggest that application of allantoin stimulates shifts in microbial community composition and increases microbial diversity as well as living microbial biomass in rice soil.