[Effects of soil water content on H2O and CO2 exchange in tomato leaves in different seasons].

With tomato variety "L402" as test crop, this paper studied its photosynthetic and transpiration 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 (Pn) and transpiration rate (Tr) of tomato leaves were the highest in treatment I , followed by treatments II and Ill, while the water utilization efficiency ( WUE) was the highest in treatment II. The decrease of soil water content changed the diurnal variations of Pn and Tr significantly, and aggravated the midday depression of photosynthesis. The tomato growing in winter had the lowest Pn and Tr in treatment mI , 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 m , and the lowest in treatment I . All of these suggested that the tomato plants cultivated in different seasons had different responses to soil water content. The diurnal variations of their Pn and Tr were significantly different, and the Pn and Tr of spring tomato were significantly higher than those of winter tomato under the same soil water content.