Oneyear old Dianthus plumarius introduced in Shanghai was used as materials to study growth dynamic of seedling height,accumulation and allocation of biomass,and photosynthetic characteristics.Also,this paper analyzed the relationship between net photosynthetic rate (P_n) and physioecological factors.The results were as follows:(1)Prosperous phase of growth of seedling height was from March to June,and increment for this period accounted for 65.93%.In general,biomass of each organ of seedling increased gradually,D.plumarius seedlings allocated more biomass to the aboveground parts during March to June,and the biomass ratio of aboveground parts to the whole plant increased from 46.89% to 65.60%.After June,the biomass ratio of aboveground parts to the whole plant increased from 34.40% to 53.11%.(2)The diurnal variation of P_n had a single curve in spring and autumn and the doublepeak curve in summer which had obvious midday photosynthetic depression.(3) The main physioecological factors affecting the characteristics of P_n of D.plumarius were transpiration rate and temperature in spring,stomatal conductance and atmospheric CO₂ concentration in summer;and intercellular CO₂ concentration and photosynthetic active radiation in autumn;The main limiting factors were intercellular CO₂ concentration and photosynthetic active radiation in spring,transpiration rate and relative humidity in summer;and stomatal conductance and temperature in autumn.(4)The light compensation point of D.plumarius was about 56.94 μmol·m^-2·s^-1 and the light saturation point was around 780.07 μmol·m^-2·s^-1,so D.plumarius is a heliophyte.