Phenolics are a dominant class of plant secondary metabolites that have strong effects on various ecosystem processes. The ecological significance of these compounds, however, is still poorly understood. We hypothesized that the inhibitory effects of phenolics on microbial activity could enhance plant nitrogen acquisition by relaxing competition between plants and microbes. To test this hypothesis theoretically, we constructed a novel and simple mechanistic model by unifying two concepts: one

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... a new paradigm of nitrogen cycling which considers the uptake of organic nitrogen by plants, and the other is that phenolics can regulate nitrogen cycling by inhibiting microbial decomposition processes. Our plant-microbe competition model consists of five compartments (plants, soil microbes, debris, organic nitrogen and inorganic nitrogen) and incorporates the essential processes of nitrogen cycling: plant uptake of monomers, competition between plants and microbes, and the depolymerization process. Our analysis showed that plant nitrogen acquisition was maximized at intermediate levels of phenolics, but only when plants could utilize organic nitrogen. Furthermore, this pattern occurred over a broad range of parameter conditions. Our study successfully demonstrated the potential role of phenolics in plant nitrogen acquisition throughout natural environments.