Abstract: The utilization rate of cucurbit vegetable to fertilizer is low in China. Summer squash is one of the main vegetables cultivated in solar greenhouse in north China. In order to improve fertilizer utilization efficiency, "Nongyuan No.1" summer squash was taken as the test material for hydroponics experiment. Seven nutrient solution treatments were set in the experiment. T1: General nutrient solution formula (control), 1/2 times Yamazaki cucumber nutrient solution formula; T2: Low formula nutrient solution, 1/3 times Yamazaki cucumber nutrient solution; Treatment T3, T4, T5, T6 and T7 were added with 7, 35, 70, 105 and 140 mg HIDS per liter of nutrient solution on the basis of T2 formula. That was to say, HIDS concentration in nutrient solution is 7, 35, 70, 105, 140mg·L−1. When summer squash seedlings had two leaves, they were planted in a 4.5L bucket of the treatment solution (2 plants per bucket). The effects of adding HIDS to low formula nutrient solution on growth, antioxidant enzyme activity, soluble sugar, protein, photosynthesis and fluorescence of summer squash were analyzed after 12 days of hydroponics in solar greenhouse. The results showed that the growth status, antioxidant enzyme activity and photosynthetic capacity of T2 summer squash treated with low formula nutrient solution were all worse than those treated with general nutrient solution T1. The addition of HIDS promoted the growth of summer squash in the low formula nutrient solution, and the concentration of HIDS in the nutrient solution was 70mg·L−1, which had the best effects on T5. Compared with T2 treatment, the leaf area, root volume, fresh and dry weight of the whole plant, soluble protein, superoxide dismutase (SOD), peroxidase (POD) and catalase (CAT) in T5 treatment were significantly increased by 13.17%, 21.69%, 12.19%, 21.28%, 23.57%, 132.22%, 44.32%, 39.61% and malondiadehyde (MDA) content was significantly reduced by 102.55%. The photosynthetic rate, transpiration rate, stomatal conductance, daily mean value of intercellular carbon dioxide and total chlorophyll content of T5 were significantly increased by 41.77%, 19.11%, 8.84%, 40.26% and 37.50% compared with T2. In addition, the addition of HIDS increased Fv/Fm, Fv'/Fm', ETR, qP and decreased NPQ in the leaves of summer squash under low nutrient solution, and alleviated the low nutrition to the summer squash photosynthesis organ damage. There was no significant difference in each index between T5 and T1. Therefore, the HIDS concentration of 70mg·L−1 in low nutrient solution could promote the growth, photosynthesis and increase the activity of protective enzymes of summer squash and could save 16.67% fertilizer.

Key words: 水培西葫芦, 螯合剂, HIDS, 低配方营养液, 光合作用