Effects of different concentrations of dissolved oxygen on the growth, photosynthesis, yield and quality of greenhouse tomatoes and changes in soil microorganisms

The effects of different concentrations of dissolved oxygen (DO; 4, 6, 7.5, and 9 mg L⁻¹, control (CK), O1, O2, and O3, respectively) on the growth, photosynthesis, yield and quality of tomatoes and changes in soil microorganisms in a greenhouse were studied. These effects were evaluated for two years via a comparative design. (1) The effects of DO on the leaf area index (LAI), net photosynthetic rate (A), vitamin C (Vc) content, soluble sugar content, lycopene content, dry matter accumulation (Dₐ), soil respiration rate, microbial carbon content, microbial nitrogen content, yield, irrigation water-use efficiency (IWUE), water-use efficiency (WUE), and soil oxygen content (SOC) were very significant (P < 0.01). (2) In 2018 (2019), the LAI, A, Vc content, soluble sugar content, lycopene content, Da, soil respiration rate, soil microbial carbon content and soil microbial nitrogen content in the O3 group increased by 25.59% (20.88%), 12.89% (36.14%), 38.39% (27.07%), 18.31% (47.67%), 18.45% (52.50%), 15.34% (12.58%), 48.33% (68.97%), 46.73% (64.38%), and 27.27% (36.84%), respectively, compared with those in the CK group. (3) In 2018 (2019), the yield, IWUE, WUE and SOC in the O3 group increased by 17.51% (15.09%), 17.48% (15.06%), 33.87% (34.97%) and 50.97% (53.34%), respectively, compared with those in the CK group. (4) The effects of aerated irrigation (AI) on the growth, photosynthesis, quality, biomass, yield, WUE and SOC of the tomatoes, as well as the soil microorganisms, were consistent such that O3 > O2 > O1 > CK, but their levels of significance differed slightly. When the DO of the irrigation water was increased, the SOC increased indirectly, the soil environment was improved, and the growth of the tomato plants increased. Moreover, these effects were also conducive to improved WUE and tomato quality and efficiency. This study provides a new irrigation model and a theoretical basis for the popularization of greenhouse crop cultivation.