Abstract: Five nitrogen (NH₄NO₃) fertilization levels (g·m^-2), i.e., 0 (CK), 10.0 (N₁), 20.0 (N₂), 40.0 (N₃) and 50.0 (N₄), were employed to evaluate the effects of nitrogen fertilization on the growth and leaf physiological characteristics of Pinus sylvestris var. mongolica seedlings on sandy soil. Indexes of growth and foliar physiology were measured in May, July, and September, respectively. Nitrogen addition significantly increased plant height, relative growth rate, and biomass per plant, but not for relative water content in leaves. Obvious proline accumulation was found for N₄ level. The highest values of biomass per leaf, plant height, basal diameter, leaf mass ratio, contents of chlorophyll (a+b), chlorophyll a and chlorophyll b were found for N₃ treatment. Nitrogen addition mainly promoted the growth of P. sylvestris var. mongolica seedlings during May to July, and the N₃ level was optimum among the five levels.

Key words: Diatom, Species composition, Ecological distribution, Changjiang River estuary