Soil salinity and nitrogen (N) distribution are often heterogeneous in the soil. However, the combined effects of salinity and N heterogeneity on plant water use efficiency (WUE) and fruit quality remain poorly understood. A split-root pot experiment was conducted with three salinity distributions, viz. S 1:5 (1‰/5‰ by mass of soil in side-A/side-B), S 2:4 (2‰/4‰) and S 3:3 (3‰/3‰), combined with three N application patterns, including N 4:0 (270/0 mg kg −1 by mass of soil in side-A/side-B), N 0:4 (0/270) and N 2:2 (135/135). Compared with S 3:3 , non-uniform salinity (S 1:5 and S 2:4 ) combined with local N supply at high-salinity side (N 0:4 ) enhanced the intrinsic WUE (WUE i , A n /g s ) and whole-plant WUE (WUE p , total dry biomass/ water use), due to reduced g s from flowering to ripening stage. Visual and storage fruit-quality traits, including fruit firmness and shape index were significantly enhanced by N 0:4 compared to N 2:2 and N 4:0 , while fruit water content was reduced. Fruit firmness increased with reduced fruit water content and a lower root dry matter ratio between side-A and side-B. Moreover, fruit Δ 13 C were significantly decreased by N 0:4 compared to N 2:2 and N 4:0 . Among all organs, fruit Δ 13 C was most strongly correlated with whole-plant Δ 13 C and WUE p , but unrelated to visual and storage traits. Localized N application in high-salinity zone enhanced water productivity and fruit visual and storage quality, offering a strategy to improve tomato performance under saline conditions. Furthermore, fruit Δ 13 C is suggested as a reliable organ-specific indicator of whole-plant water status under heterogeneous salt and N conditions.
Liu et al. (Sat,) studied this question.