Effects of source reduction on photosynthetic rate, dry mass and distribution in pumpkin

The four treatments were designed for studying the effects of source reduction by removing leaves on photosynthetic rate, dry mass and distribution in pumpkin, including that the source was reduced to 25% (T1), to 50% (T2), to 75% (T3), and CK. The results showed that when the source reduced to 25%, the photosynthetic rate of leaves behind fruit dropped first, followed by the fruit leaves and leaves in front of fruit. In contrast, the photosynthetic rate remained the same when the source reduced to 75%. Under cloudy weather condition, the photosynthetic rate showed the same variation trend with light radiation, including a unimodal curve with the peak between 14:00–16:00 PM. On the sunny day, the photosynthetic rate showed a single peak curve while the photosynthetic rate showed a bimodal curve. Whenever in the cloudy or sunny day, the photosynthetic rate in T3 was significantly higher than other treatments; however, there was no significant difference on photosynthetic rate between T2 and CK. When the source reduced to 75%, the total dry mass increased 18.66%, while it decreased 36.25% when reduced to 25%. With more reduction of the source, the flux of photosynthetic products to the sink became more efficient. Therefore, during the flowering and early fruit development stage in pumpkin, appropriate source reduction by removing some leaves on vine not only maintained the photosynthetic rate, but also improved the flux from source to sink, thereby increasing the accumulation of total dry mass and yield.