Abstract: We studied the growth(height, ground diameter, biomass) dynamic, biomass allocation, relative growth rate and leaf photosynthesis of Betula platyphylla bare-rooted seedlings under constant fertilization(CF), exponential fertilization(EF) and 1.5 exponential fertilization(EF1.5) regimes in one growing season. Dynamic of seedling height, ground diameter and biomass presented the same tendency, which barely showed difference in the early growing stage between three treatments, while both EF and EF1.5 were significantly higher than CF in the late growing period; however, EF and EF1.5 were not significantly different. At the end of the growing season, EF1.5 seedlings were the tallest, EF and EF1.5 seedlings were 18.2% and 25% taller than CF, respectively(P>0.05). EF seedlings owned the thickest ground diameter, EF and EF1.5 were 11.2% and 5.8% thicker than CF, respectively(P<0.05). The biomass sequence of each plant between three treatments was EF>EF1.5>CF, and EF and EF1.5 were 41.5% and 25.4% higher than CF, respectively(P<0.05). Stem biomass, leaf biomass and root biomass under EF and EF1.5 were both significantly higher than those under CF(P<0.05). Height, ground diameter and biomass RGR under EF and EF1.5 were both significantly higher than those under CF(P<0.05), and biomass RGR was EF>EF1.5(P<0.05). During the fast-growing periods of seedlings, EF treatment promoted seedling leaf photosynthetic characteristics. The seedling leaf area under EF treatment was 16.8% greater than that under CF treatment(P<0.05). Chlorophyll content and photosynthetic rate were increased by 4.5%(P>0.05) and 5.0%(P>0.05). EF and EF1.5 promoted seedling growth and biomass accumulation obviously than CF. EF saved a large amount of fertilizer than EF1.5, and promoted seedling growth similarly. Therefore, EF is the best treatment.

Key words: Betula platyphylla, bare-rooted seedlings, exponential fertilization, growth dynamic, biomass allocation