Abstract: Nitrogen and phosphorous are the two basic elements needed for plant growth, we carried out this experiment with two different levels of nitrogen (0, 60 kg·ha^-1) and three difference levels of phosphorous (0, 60, 90 kg·ha^-1) addition treatments, to investigate the effect of fertilizer addition and daily light radiation on the photosynthetic characters on Festuca kryloviana by analysis the leaf gas exchanges parameters and chlorophyll fluorescence parameters. As the results shown, the photosynthetically active radiation increased and decreased in the daytime, the peak value was at 13:00 p.m. 2000 μmol·m^-2·s^-1, and which the effect on the photo index were more significant than the fertilizer addition. Net photosynthetic rate (P_n) increased first then decreased with the increasing photosynthetically active radiation and its value was the highest at 800-1000 μmol·m^-2·s^-1. The change of stomatal conductance (G_s), stomatal limited value (L_s), transpiration rate (T_r), water use efficiency (WUE) were consistent with P_n, but the intercellular CO₂ concentration (C_i) was opposite. After the nitrogen and phosphorus addition, G_s, L_s and T_r increased, and C_i decreased, indicated that the increase of P_n after fertilization were mainly by the increasing of the water and CO₂ exchange among the leaves and the environment. With the increasing of photosynthetically active radiation, the effective photochemical efficiency of PSⅡ (F_v'/F_m'), the actual photochemical efficiency of PSⅡ (Φ_PSⅡ) and the photochemical quenching coefficient (qP) were significantly reduced, the non-photochemical quenching coefficient (NPQ) increased significantly and the electron transport rate (ETR) increased first and then decreased, the scale was among the 400 to 800 μmol·m^-2·s^-1 and changed rapidly after 1200 μmol·m^-2·s^-1. Nitrogen and phosphorus fertilizers significantly increased F_v'/F_m', Φ_PSⅡ, qP and ETR. In particular, N₆₀P₉₀ treatment also increased the maximum photochemical efficiency of PSⅡ (F_v/F_m) and NPQ. In terms of light energy allocation and alleviate the light damage, versus thermal dissipation (D) and excess (E) were increased and the proportion of photosynthetic electron transport (P) decreased with the increasing of photosynthetically active radiation. The above results showed that from the photosynthetic characteristics of the leaves of F. kryloviana, the application of nitrogen and phosphorus fertilizers increased the leaves P_n through adjust G_s that enhancing of water and CO₂ exchange between the leaves and the environment and increased the activity of the PSⅡ and P by reducing the proportion of E.

Key words: Festuca kryloviana, combined application of nitrogen and phosphorus fertilizers, flowering period, gas exchange parameters, chlorophyll fluorescence parameters, light energy allocation