Abstract: Four treatments (normal soil water condition, CK; light drought condition,T₁; water saturation condition, T₂; and submersion condition, T₃) were installed to study the responses in leaf photosynthesis and chlorophyll fluorescence parameters of slash pine (Pinus elliottii Engelm.) seedlings to different soil water regimes. Differences were observed in the responses of the leaf gas exchange parameters, water use efficiency (WUE), photosynthetic pigment contents, and chlorophyll fluorescence parameters to the soil water regimes. The photosynthetic pigment contents were the lowest in treatment T₃, and the net photosynthetic rate (P_n), electron transport rate (ETR), and quantum yield of PSII photochemistry (Φ_PSII) were lower in treatments T₂ and T₃, as compared with CK. The slash pine seedlings in treatmentT₃ still had a higher P_n than the other plant species that have high tolerance to inundation, indicating that the slash pine seedlings had high tolerance to inundation. In treatment T₁, the seedlings kept high WUE, low stomatal conductance (G_s), and low transpiration rate (T_r) against the drought stresses, while decreased P_n, potential efficiency of primary conversion energy of PSII (F_v/F_m),ETR, and Φ_PSII, though these parameters were still maintained at relatively normal level. The above results suggested that slash pine seedlings could not only tolerate water-logging, but also endure a certain degree of drought, and that slash pine could be a candidate species in re-vegetation of the Three Gorges Reservoir region.

Key words: savoy, light quality, chlorophyll, photosynthetic characteristics, nutritional quality.