Abstract: This paper studied the effects of three levels of shading (no shading, 75% shading and 40% shading) for 8 days on tomato leaf photosynthesis, drymatter partitioning and yield formation at three growth stages 1i. e. early flowering (EF) , peak flowering (PF) , late flowering (LF) 2. Different effects caused by shading at different growth stages were found. Shading caused a higher increase in stomatal conductance and intercellular CO₂ concentration at all three growth stages compared with unshaded plants, significantly reduced the midday net photosynthetic rates at most days of the EF stage, but the photosynthetic rates in 40%2shaded leaves at PF stage were increased gradually depending on the length of the shading time. This trend become more obvious and the average photosynthetic rates during a 82day shading period in 40% shading treated leaves was increased by 22% at
the LF stage. The 75% shading treatment reduced the drymass of root and stem tissues at the EF and PF stages, while the 40% shading region increased root dry mass and stem dry mass by 43% and 22% compared with the unshaded treatment at the LF stage. The influence of shading on the dry mass of leaves was very small at most growth stages. A 40% shading treatment at the LF stage significantly enhanced the fruit yield, but failed to affect the fruit yield at the EF stage. The results showed that tomato could growwell and a better yield could be obtained if some moderate shading ( i. e. 40% shading) was applied at the LF stage in the summer midday time.

Key words: Shading, Tomato, Different growth stages, Photosynthesis, Yield