Interactive effects of salinity and drought stress on photosynthetic characteristics and physiology of tomato (Lycopersicon esculentum L.) seedlings

Sufficient quantity and quality of water are essential for vegetable production. Evaluating the individual and combined effects of drought and salt stress on plant establishment may help inform management of plant production in terms of stabilizing yield. This study investigates the effects of drought and salt stress on plant growth, nutrition elements, and select physiological parameters of tomato (Lycopersicon esculentum L. cv. H2274) through a pot experiment under greenhouse conditions. Drought stress was applied to tomato seedlings at 3 different levels of irrigation: D0 (control), D1, and D2 at 100%, 75%, and 50% field capacity, respectively. Salinity stress was applied at 3 different doses S0, S1, and S2 at 0 mM, 100 mM, and 150 mM NaCl, respectively. The effects of salinity, drought and their co-occurring stresses on growth, physiological and photosynthetic properties of tomato seedlings were statistically significant. Photosynthetic rate (Pn), stomatal conductance (gs), chlorophyll reading value (CRV), and plant dry weight (DW) decreased with salt and drought treatments. However, electrolyte leakage (EL) of the leaves increased with increasing salt and drought treatments. Fresh weight (FW) of the tomato seedlings decreased 67% under the 150 mM NaCl treatment (S-2), and decreased 69% under severe drought (D2); however, the interactive effects of these two treatments together (S2D2) resulted in an 80% decrease in FW. Furthermore, dry weight (DW) decreased 80% in the S2D2 treatment compared to the control. In general, both drought and salinity altered the mineral nutrient composition by decreasing N, P, K, Fe, Ca and Z content of the tomato seedlings, but Na, B and Cl content increased. These results show that effects of salinity and drought on tomato seedlings were less detrimental for plant establishment than the combined effects of the two stresses together.