Cucumber (Cucumis sativus L., cv. ‘Jinyou No. 4’) seeds were
obtained from Tianjin Kernel Cucumber Research Institute, China.
The seeds were germinated on two layers of wet filter paper in
Petri dishes in the dark for approximately 24 h at 29 ± 1 ◦C. The
germinated seeds were sown in sand and moved to a plant growth
chamber (Ningbo Jiangnan Instrument Factory, Ningbo, China) at
Nanjing Agricultural University, Nanjing, China. The growth chamber
was kept at 28 ± 1 ◦C (day) and 19 ± 1 ◦C (night) with relative
humidity (RH) of 50–60%. The maximum photosynthetic photo flux
density (PPFD) was approximately 1200 mol m−2 s−1. When the
second leaves were fully expanded, 12 seedlings were transplanted
into plastic containers containing half strength Hoagland solution
(Table 1). The nutrient solution was aerated using an air pump at an
interval of 20 min to maintain the dissolved oxygen concentration
at 8.0 ± 0.2 mg L−1 during this experiment.