Abstract: An investigation was made on the dynamic changes of tannin concentration in Syzygium jambos and Dracontomelon duperreanum leaves over a 105-day period of leaf litter decomposition in a second-order stream in Longdong Reservoir, Guangzhou. The initial tannin concentration in S. jambos leaves (0.191 g·g^-1 DM) was higher than that in D. duperreanum leaves (0.057 g·g^-1 DM). In the first week of leaf litter decomposition, the tannin concentration in D. duperreanum and S. jambosleaves decreased by 45% and 22% respectively. 21 days after, the decline in tannin concentation slowed down, but the decomposition rate increased, with the leaves of D. duperreanum decomposed faster than those of S. jambos (k value was 0.038 d^-1 and 0.013 d^-1, respectively). The average density of benthonic invertebrate colonized on D. duperreanum leaves (287.9 ind·g^-1 leaf mass) was significantly higher than that on S. jambos leaves (26.2 ind·g^-1leaf mass) (P<0.05). A continual increase of benthonic invertebrate’s abundance was observed during leaf litter decomposition, which could be attributed to the rapid decrease of leaf tannin concentration. The slower breakdown of S. jambos leaf litter was likely because of the high tannin concentration in S. jambos leaves, which inhibited benthonic invertebrate, especially the shredder’s colonization. 

Key words: tannin, leaf litter, breakdown, benthonic invertebrate, phytoplankton, environmental factor, canonical correspondence analysis, Nansha Islands.