Abstract:Effects of tannin extracted from Casuarina equisetifolia branchlets on the growth and tannin contents of its seedlings were studied. The tannins extracted from C. equisetifolia branchlets significantly inhibited the seedling growth, and the inhibition enhanced with increasing of tannin concentration. Under the same concentrations of tannins, sprout growth was inhibited more significantly than root growth treated after 15 days. The contents of tannins, especially total phenolics and extractable condensed tannins in seedlings decreased with increasing of extracted tannin concentrations. The significant linear negative correlation between them demonstrated that tannins extracted from C. equisetifolia branchlets had significant allelophthic effects on the seedlings. The allelophthic effects impacted not only the growth of C. equisetifolia seedlings, but also resistance against herbivore and other detrimental factors through impacting the formation of secondary metabolites in seedlings.