Lowering medium pH improves tolerance of tomato (Lycopersicon esculentum) plants to long-term salinity exposure

Abstract

Although salinity stress adversely affects plant function, manipulation of the rhizosphere may alleviate those negative impacts. We examined whether adjustment of rhizosphere pH, unadjusted control (∼pH 8.5–9), pH 5.5, and pH 4.5 would mitigate adverse effects of salinity on tomato plants (cv. Mobil) in hydroponics. Plants were evaluated based on the leaf chlorophyll parameters, plant survival, leaf water relations, and yield. Chlorophyll fluorescence parameters were lowest at 28 days after salinity onset (DAS). The maximum PSII quantum yield (F_v’/F_m’) and operating efficiency (ΦPSII) were recorded in plants grown in pH 4.5 at 56 DAS. At 28 DAS, the linear electron transport rate (J) was decreased by 10 and 13%, in control and pH 5.5, respectively, compared with the day zero. The fraction of photons used in photochemistry (%P) was suppressed at 28 DAS, but %P was the greatest under 4.5 pH at 56 DAS. Stomatal conductance and leaf osmotic potential (Ψ_O) were negatively correlated. Plants grown at pH 5.5 had the greatest fresh fruit weight and plant dry weight compared with the other pH levels. Although salinity adversely affected plant performance, lowering rhizosphere pH alleviated the adverse impacts of salinity. It seems that the tomato variety ‘Mobil’ used to measure leaf chlorophyll fluorescence parameters in this study had a salinity tolerance to which was enhanced at more acidic pH.

Keywords:

• Fruit weight
• hydroponics
• light-adapted chlorophyll fluorescence
• photochemistry
• quantum yield of PSII
• rhizosphere acidity

Declaration of interest statement

There is no conflict of interest.