Effects of elevated CO2 and nitrogen supply on leaf gas exchange, plant water relations and nutrient uptake of tomato plants exposed to progressive soil drying

Abstract The effects of nitrogen (N) supply on the response of leaf gas exchange, leaf water relations and plant nutrient uptake of tomato plants exposed to progressive soil drying under elevated CO2 (e[CO2], 800 ppm) were investigated. Two tomato genotypes differing in their endogenous abscisic acid (ABA) level, i.e. Ailsa Craig and its ABA-deficient mutant (flacca) were grown in pots in greenhouse cells with either ambient CO2 (a[CO2], 400 ppm) or e[CO2]. Two N levels, i.e., N1, 0.5 g pot−1 and N2, 1.0 g pot−1 were used and the N fertilizer (NH4NO3) was applied with the irrigation water before transplanting. The results showed that e[CO2] and N2 increased photosynthesis and water use efficiency (WUE) of tomato plants. N2 improved plant water relations by sensitizing the decline of transpiration rate during soil drying. The plant N acquisition and major ionic concentrations in xylem sap were lowered under e[CO2], such negative effect was compensated by increasing N supply. For WT, the ABA concentrations in leaf ([ABA]leaf) and xylem sap ([ABA]xylem) were increased with the decrease of the fraction of transpirable soil water, whereas, for flacca this was only observed in [ABA]leaf. Compared to WT, flacca had lower xylem sap ionic concentrations and WUE. Collectively, the responses of tomato plants to e[CO2] and N supply under progressive soil drying were genotypic-dependent, and endogenous ABA level could play an important role in modulating the responses.