Silicon Compensates Phosphorus Deficit-Induced Growth Inhibition by Improving Photosynthetic Capacity, Antioxidant Potential, and Nutrient Homeostasis in Tomato

Phosphorus (P) deficiency in soils is a major problem for sustainable crop production worldwide. Silicon (Si) is a beneficial element that can promote plant growth, development and responses to stresses. However, the effect of Si on tomato (Solanum lycopersicum L.) growth, photosynthesis and mineral uptake under P deficit conditions and underlying mechanisms remain unclear. Here, we showed that low P (LP) supply inhibited tomato growth as revealed by significantly decreased fresh and dry weights of shoots and impaired root morphological traits. LP-induced growth inhibition was associated with decreased photosynthetic pigment content, net photosynthetic rate (Pn), stomatal conductance, transpiration rate and water use efficiency. However, exogenous Si application alleviated LP-induced decreases in growth and physiological parameters. In particular, Si increased Pn by 65.2%, leading to a significantly increased biomass accumulation. Biochemical quantification and in situ visualization of reactive oxygen species (ROS) showed increased ROS (O-2(-) and H2O2) accumulation under LP stress, which eventually elevated lipid peroxidation. Interestingly, exogenous Si decreased ROS and malondialdehyde levels by substantially increasing the activity of antioxidant enzymes, including superoxide dismutase, peroxidase, and catalase. In addition, Si increased concentrations of osmoregulatory substances, such as proline, soluble sugar, soluble proteins, free amino acids, and organic acids under LP stress. Analysis of major element concentrations revealed that exogenous Si application under LP stress not only increased Si uptake but also enhanced the concentrations of most essential elements (K, Na, Ca, Mg, Fe, and Mn) in different tissues (roots, leaves, and stems). These results reveal that Si mitigates LP stress by improving photosynthetic capacity, antioxidant potential, and nutrient homeostasis and that it can be used for agronomic management of vegetable crops in P-deficient soils.