Soil pH controls nitrification and carbon substrate utilization more than urea or charcoal in some highly acidic soils

Understanding the mechanism and key controlling factors of nitrification in highly acidic soils is important from both ecological and environmental perspectives. Many acid soils are also characterized by vegetation that produces polyphenolic and terpene compounds that inhibit microbial activity. We investigated the potentially ameliorative effects of lime, charcoal, and urea additions on soil nitrification and carbon substrate utilization (using the MicroResp method). Four soils were studied from widely different environments but with similar pH and inputs of phytochemicals to determine the relative effects of these potentially controlling factors. The addition of charcoal had no significant effect on net nitrification, but charcoal significantly increased soil basal respiration and altered C substrate utilization in the two Scottish soils. Urea greatly increased nitrification in both the Chinese soils, but there was no effect of urea on nitrification in the two Scottish soils. Lime application increased nitrification in all the soils except for the Chinese mixed forest soil. Multivariate analysis of the C source utilization data revealed that lime altered C substrate utilization more than urea or charcoal in these highly acidic soils. Our results suggest that acid-tolerant nitrifiers do exist in these soils and have potential for high activity, and pH (lime addition) and N-substrate (urea) most often increased nitrification. However, no single factor controlled nitrification in every soil, suggesting an interaction between abiotic and nitrifier community composition as a result of land use and soil type interactions.