Phenolic inputs by invasive species could impart seasonal variations in nitrogen pools in the introduced soils: A case study with Polygonum cuspidatum

► Inorganic-N and mineralization lower inside than outside in spring but became higher by fall. ► Carbon and nitrogen mineralizing enzymes lower inside than outside. ► Amino acids, organic N and phenolic compounds showed the opposite seasonal pattern. ► Exogenous addition of knotweed tannin reduced N-mineralization and replicated field observations. ► The influence of invader on soil chemistry limited to top 5 cm of the soil.