Synergistic regulation of photosynthesis, antioxidants, and fruit weight in greenhouse-grown tomato as affected by substrate type and exogenous additives

Water scarcity severely constrains the development of substrate-based cultivation in greenhouse systems in the Gobi region. Optimizing root-zone water regulation through exogenous additives is a key approach to improving water use efficiency; however, the physiological mechanisms underlying the synergistic effects between different substrates and exogenous additives remain unclear. In this study, greenhouse-grown tomato was used as the experimental material. Three cultivation systems were established: coconut coir, washed sand, and a mixed substrate (peat + perlite), combined with the application of a surfactant, a nano water-retaining agent, and their combined treatment. In the coconut coir and mixed substrate systems, the sole application of the surfactant significantly increased stomatal conductance, net photosynthetic rate, and peroxidase (POD) activity, with each variable increasing by approximately 28–42 % relative to the corresponding control, while reducing malondialdehyde (MDA) content ranged from 12–26 %. In the washed sand substrate, the combined treatment increased the peak net photosynthetic rate by 32.6 % and simultaneously enhanced superoxide dismutase (SOD) and POD activities. POD activity was highly significantly positively correlated with net photosynthetic rate, stomatal conductance, and average fruit weight. Substrate type partially determined the efficiency-enhancing pathways of exogenous additives. The appropriate matching of substrate and additives synergistically promoted photosynthetic carbon assimilation and average fruit weight formation, with gains ranging from 4.1 % to 12.4 % depending on the treatment combination. This study provides a feasible strategy for water-saving and efficient production in Gobi greenhouse agriculture.