Effect of rain shelters and drought on leaf water status and photosynthetic parameters in tomato

The present study explored the effect of rain shelter and drought on photosynthetic activity and changes in leaf water status. Tomatoes were grown in the trial plot located at Hohai University, China, in 2011 and 2012, and allotted to five treatments [80% field capacity under open field (T1, control) and rain shelter (T2), 70%, 60%, and 50% of T2 (T3, T4, and T5)]. The lowest sap flow rate and relative water content and the highest values for specific leaf area were obtained from plants in T5. T2 decreased the average net photosynthetic rate (PN) by 5.35% compared to the control, although there was no reduction in intercellular CO2 concentration and stomatal conductance. The average reduction of transpiration rate registered under rain shelters was only around 10.2% in both the years. The PN, maximum quantum yield of PSII photochemistry (Fv/Fm) and activity of the water-splitting complex on the donor side of the PSII (Fv/Fo) decreased with irrigation volume. Quenching analyses showed the development of a lower photochemical quenching (qP) in plants under rain shelters, accompanied by the development of a higher nonphotochemical quenching (qN). Drought-stressed tomato exhibited a decrease in qP parallel to an increase in qN.