A pot experiment was carried out to study the effect of decomposing leaf litter of Eucalyptus grandis on the growth and photosynthetic traits of two forage grass species (Elymus sibiricus and Trifolium pratense),and as well as on the activity dynamics of several soil enzymes.Leaf litter was applied at rate of 0,50,100,150 gram per pot,each containing 8 kg soil,resulting into four treatments,i.e.,CK,L⁵⁰,L¹⁰⁰ and L¹⁵⁰,respectively.Results were shown as follows:(1)Tussock height and biomass production in both grasses decreased with the increasing rate of leaf litter,and the inhibition effect declined as the exposure time prolonged.(2)Application of leaf litter promoted the photosynthetic rate (Pⁿ),expanded the adaptation interval of light intensity and CO² concentration,and increased the apparent quantum yield (AQY) (except treatment L¹⁵⁰) and carboxylation efficency of rubisco (CE) of E.sibiricus.Comparatively,decomposition of leaf litter resulted in the expansion of light utilization,but the shrink of CO² utilization in T.pratense species.Meanwhile,Pⁿ,AQY and CE of T.pratense were only promoted by treatment L⁵⁰.For both target plants,the dark respiration rate (R^d) or/and photorespiration rate (R^p) were generally increased by application of leaf litter at three rates.(3)An average synthesis effect of 0.317 and 0.380 were observed in T.pratense and E.sibiricus,respectively and the former exhibited stronger resistance ability.(4)Similarly,the activities of phosphatase and saccharase increased during 20~60 d and 20~40 d,respectively,but with the passage of time the promotion effect on activities of both enzymes decreased,which was in accordance with the inhibition dynamics on tussock height.Neither the urease activity nor the catalase activity was altered to a large extent by the leaf litter decomposition.Based on the results,we concluded that the decomposition of E.grandis leaf litter affects the growth of both grass species directly or indirectly by releasing allelochemicals.Despite that the two grass species may respond to this effect by enhancing the ability to utilize light and CO²,their growth was limited throughout the experiment period,because their energy consumption rate was promoted.