Abstract: Photosy nthetic rate at 30℃ root temperature was the biggest.Photosynthetic rate decreased at lower or higher root temperature, and reached its low est value at 40℃ root temperature.The mechanism of the influence of root temperature on photosynthesis was different at different root temperature.15℃ root temperature affected photosynthesis throug hreduction of chlorophyll content and increment of its a/b ratio; 40℃ root temperature affected photosynthesis through decrease of leaf conductance or internal CO₂ concentration of leaf, and the accumulation of photosynthate in leaf; at 20-30℃ root temperature, mesophyll resistance or other factor maybe was dominant factor of lomiting photosynthesis.Transpiration rate was the highest at 30℃ root temperature, but the water utilization ratio is the lowest.Transpiration rate decreased when root temperature increased or decreased, but water utilization ratio increased.Stomata closed partially at lower root temperature; at higer root temperature, stomata closed and resistance of root increased.

Key words: Tomato, Root temperature, Photosynthesis, Water metabolsim