Abstract:Plant polyphenol (PP) and low molecular weight organic acid (LMWOA) have important effects on the transformation of iron fraction in soil. In this study, acidic, neutral and calcareous purplish soils were used as research objects, incomplete randomized block experiments were performed by using two kinds of PPs (i.e., epigallocatechin gallate (EGCG) and rutin) and two LMWOAs (i.e., citric acid and oxalic acid). After the solution was leached, soluble iron (Fes), free Fe oxides (Fed), amorphous Fe oxides (Feo), and organic-bound Fe (Fep) were measured to investigate the effect of PPs and LMWOAs on iron transformation in purplish soil. The results showed that both PP and LMWOA could increase Fes content in acid purplish soil, decrease Fes content in neutral purplish soil. For calcareous purplish soil, PP promoted but LMWOA decreased Fes content. When EGCG and LMWOAs were combined, both acidic and calcareous purplish soils showed that LMWOAs weakened EGCG's promoting effect on Fes by promoting iron transformed into Fep instead of being transformed into Fes. When rutin was used in combination with LMWOAs, the synergistic effect was observed in acid purplish soil, LMWOAs inhibited rutin promotion effect on Fes. In neutral purplish soil, the combined action of PPs and LMWOAs reduced the inhibition of PPs on Fes by promoting Fed converted into Fes.