Abstract: With tomato variety “L402” as test crop, this paper studied its photosynthetic and tran-spiration characteristics in different seasons under different soil water contents. Three treatments were installed, i . e ., 80% (Ⅰ), 65% (Ⅱ) and 50% (Ⅲ) soil water content. The results showed that when cultivated in spring, the photosynthetic rate (P_n) and transpiration rate (T_r) of tomato leaves were the highest in treatment Ⅰ, followed by treatmentsⅡ and Ⅲ, while the water utilization efficiency (WUE) was the highest in treatment Ⅱ. The decrease of soil water content changed the diurnal variations of P_n and T_r significantly, and aggravated the midday depression of photosynthesis. The tomato growing in winter had the lowest P_n and T_r in treatment Ⅲ, while no difference was observed between treatments I and II.No midday depression of photosynthesis was found among the three treatments. The WUE was the highest in treatment Ⅲ, and the lowest in treatment Ⅰ. All of these suggested that the tomato plants cultivated in different seasons had differ-ent responses to soil water content. The diurnal variations of their P_n and T_r were significantly differ-ent, and the P_n and T_r of spring tomato were significantly higher than those of winter tomato under the same soil water content.

Key words: Frankia, Natural stress, Genetic diversity