Exogenous silicon application improves fruit yield and quality of drip-irrigated greenhouse tomato by regulating physiological characteristics and growth under combined drought and salt stress

Abstract

Improving crop productivity in drought-stressed and salt-affected regions is the key to promoting sustainable agriculture. Silicon is considered to improve the stress tolerance of crops, but how exogenous silicon application affects the fruit yield and quality of tomato under combined drought and salt stress remains unclear. A greenhouse experiment was conducted over two consecutive growing seasons (autumn 2021 and spring 2022) to investigate the effects of exogenous silicon application on leaf greenness, photosynthesis and chlorophyll fluorescence parameters, fruit yield and quality of drip-fertigated greenhouse tomato under various drought and salt stresses. There were three irrigation levels: I1 (90–100% θf, where θf is the field capacity), I2 (70%–80% θf) and I3 (50%–60% θf), two soil salinity levels: S0 (0.1%) and S1 (0.4%), and two silicon application rates: T0 (0 mmol L−1) and T1 (2.4 mmol L−1), resulting in a total of 12 treatments with three replicates. The results showed that the combined drought and salt stress significantly reduced leaf silicon content, plant height, leaf area index, aboveground biomass, net photosynthetic rate, transpiration rate and stomatal conductance of tomato plants, while the exogenous silicon application promoted these parameters. Irrigation level, salinity level, silicon rate and the interaction of irrigation level and salinity level had significant effects on fruit yield. Compared to S0, S1 decreased fruit yield by 18.42%, 17.91% and 20.64% under I1, I2 and I3, respectively. Exogenous silicon application significantly improved fruit yield by 6.52% (I3S0) - 17.73% (I2S1). Irrigation level, salinity level and silicon rate had inconsistent effects on fruit quality. Exogenous silicon application significantly increased total soluble solids, Vitamin C, soluble sugars and lycopene content, without significant effect on titratable acid. The lower irrigation level and higher salinity level resulted in better fruit quality. The path analysis showed that leaf silicon content, net photosynthetic rate, lycopene, average fruit weight had significant direct positive effects on fruit yield. The results are informative for improving drip-fertigated greenhouse tomato productivity and quality under drought-stressed and salt-affected conditions.