Effects of rice phenolic acids on microorganisms and enzyme activities of non-flooded and flooded paddy soils

Benzoic acid and ferulic acid are ubiquitous allelochemicals responsible for the rice allelopathy in paddy ecosystem. We studied the effects of applied benzoic and ferulic acids on dynamic changes in the microbial biomass C, culturable microbial populations and activities of several enzymes in non-flooded and flooded incubated paddy soils. We found that benzoic acid and ferulic acid stimulated the microbial biomass C and populations as well as enzyme activities in non-flooded paddy soil, but inhibited these parameters in flooded paddy soil during the late incubation period. However, the dehydrogenase and polyphenoloxidase activities were stimulated throughout the incubation time. Thus phenolic acids in paddy soil could exert different effects on microbial biomass C, culturable microbial populations and enzyme activities and their effect varied greatly with cultivated conditions (especially water content in paddy soils). These results suggested that phenolic acids play some roles in rice allelopathy, indirectly through soil microbial processes and directly through weed suppression.