Contribution of fungi to acetylene-tolerant and high ammonia availability-dependent nitrification potential in tea field soils with relatively neutral pH

This study was conducted to analyze the relative contribution of nitrifying microbial groups in tea field soils with relatively neutral pH where high ammonia availability was expected after heavy fertilization. The nitrification potential in tea field soils supplied with organic fertilizers (OF) or chemical fertilizers (CF) was determined by the chlorate-inhibition method. The response of the potential to the net ammonia concentration, which was employed as an index of ammonia availability, was tested by loading various levels of ammonium sulfate to soil slurries. The potential of tolerance to 10 Pa acetylene was highlighted. The acetylene-tolerant nitrification potential occurred all year at a significant level. It was stimulated by ammonia availability of more than 10−5.5 mol NH3 L−1, where the nitrification potential determined under an acetylene-free condition (total potential) was affected negatively. As the test results show, the contribution of the acetylene-tolerant potential ranged from 2 to 38% with OF soils and from 8 to 67% with CF soils. These indicated a significant contribution of heterotrophic microorganisms to the nitrification potential of these neutral tea soils. The addition of cycloheximide rather than streptomycin remarkably suppressed the acetylene-tolerant nitrification potential, suggesting the primary contribution of fungi. A new aspect of heterotrophic nitrification was identified.

► We examined acetylene-tolerant nitrification in tea soils with relatively neutral pH. ► The acetylene-tolerant nitrification potential occurred all year at a significant level. ► The potential was high under an ammonia availability range excess for AOB. ► The potential was attributed to heterotrophic microorganisms. ► Fungi largely contributed to the acetylene-tolerant nitrification potential.