Abstract:In order to explore the acclimation of Fraxinus mandshurica and Quercus mongolica to light regimes and the optimal light for growth, 2-year-old F.mandshurica and Q.mongolica were cultivated under four light intensity regimes (100%, 75%, 50% and 25% of full light, which were termed as FL, LS, MS and HS, respectively). The parameters of gas exchange, chlorophyll content (Chl), leaf mass per unit area, growth, and biomass allocation were determined during the growth season. The results showed that leaf dry mass per unit leaf area (LMA), leaf fresh mass per unit leaf area (LFA), root/shoot ratio of these two species were decreased along with the decreasing irradiance; Chlorophyll content (Chl) was increased(p<0.05) with the decreasing irradiance; Light compensation point (LCP) and dark respiration rate (Rd) were in a “N” form change, but the differences are not significant(p>0.05); F.mandshurica had the greatest Pmax and the smallest Rd under HS, Q.mongolica had the greatest Pmax and small Rd under LS; Height growth of full light treatment was lower than that of the HS for these two species, basal diameter growth of full light treatment was higher than that of the HS. The results suggested that F.mandshurica was moderately shade-tolerant at the seedling stage, and the growth was better under the low light intensity; The requirement of Q.mongolica to light is higher and growth was better under relatively high light intensity.