Alternate drip irrigation with moderate nitrogen fertilization improved photosynthetic performance and fruit quality of cucumber in solar greenhouse

•Alternate drip irrigation (ADI) significantly increased the photosynthesis of cucumber.•ADI with moderate/high nitrogen improved net photosynthetic rate but not transpiration.•ADI with high nitrogen limited further increase in net photosynthetic rate due to CO2. Compared with conventional drip irrigation (CDI), alternate drip irrigation (ADI) required only moderate nitrogen fertilization to improve cucumber yield, but their effects on cucumber physiology are unclear. We investigated the coordinated effects of irrigation (CDI and ADI) and nitrogen fertilization (0, 320, and 640 kg N hm−2) on photosynthetic performance and fruit quality of cucumber (Cucumis sativus L.) in solar greenhouse. Results showed that, at moderate and high levels of nitrogen application, leaf Rubisco activity, total nitrogen and total carbon were higher in the ADI treatment than in the CDI treatment, while leaf C/N and fruit nitrite content were significantly decreased. In addition, the soluble sugar content of the fruit was significantly higher in the ADI1 treatment than in the CDI1. The photosynthetic pigment content in the leaves of ADI2 treatment was significantly higher than that of CDI2 treatment. Under the same drip irrigation method, the ADI1 and ADI2 treatments significantly increased photosynthetic pigment content, photosynthetic capacity, Rubisco activity and C/N, and significantly reduced chlorophyll a/b ratio and fruit nitrite content compared to the ADI0 treatment. However, photosynthetic parameters and fruit quality did not differ significantly between the ADI1 and ADI2 treatments.