The role of hydraulic lift in tomato yield and fruit quality under different water and salt stresses

In an arid region, water shortage limits agricultural development, and worse, soil salinization is accompanied by soil moisture drought. In this region, hydraulic lift occurs due to the drying upper layer caused by high precipitation and the wet lower layer. Hydraulic lift is defined as water redistribution from wetter, deeper soil layers to drier, shallower soil layers near the soil surface through the plant roots. To examine the effects of water and salt stresses on tomato yield and fruit quality under the condition of hydraulic lift, a 2-year experiment was conducted. Different water and salt treatments were designed, including three water levels (W1, W2 and W3 indicating soil moisture contents of 60%-70%, 50%-60% and 40%-50% of the field capacity, respectively) and four salt levels (S0, S1, S2 and S3 indicating NaCl addition of 0%, 0.2%, 0.4% and 0.6% of the dry soil weight, respectively) of the upper pot, and water and salt levels of control treatment (CK) were W1 and S0, respectively. The yield under other treatments significantly decreased by 4.59%-58.39% and 5.12%-62.96% in 2018 and 2019, respectively, compared with that under CK, and the yield under W1S1 treatment had no significance with that under CK in 2018. The firmest fruit quality was observed in the plant under W3S1 treatment, and the percentage increases were 28.67% and 28.89% in both years compared with that under CK. Water, salt stress and their interactions had significant effects on tomato taste quality and vitamin C. Tomato taste quality and vitamin C decreased under the W3 and S3 treatments. In both years, the total magnitudes of hydraulic lift during the entire growth period were higher under the W1S2 treatment (65.20% and 76.06%, respectively) than that under CK. Whereas yield and total magnitudes of hydraulic lift were significantly both correlated with single fruit weight, single fruit volume, fruit shape index and taste qualities, no correlations were observed between hydraulic lift and yield. Mild water-deficit and salt stresses could improve tomato quality with negligible yield loss, and hydraulic lift had positive effects on fruit quality. Principal component analysis revealed that the combination of W1 and S1 treatments increased fruit quality and total hydraulic lift magnitudes with an acceptable yield decline. These results are important for tomato production in arid saline-alkali region where hydraulic lift is positively corelated with fruit quality and famers may consider this trait to resist drought and soil salinization. Future studies focusing on the effects of the internal mechanisms of hydraulic lift caused by changes in sap flow on tomato quality and yield are warranted.