Investigation of Salinity and Drought Stress on Plant Water Uptake Reduction under Simultaneous Stress Condition

This study was conducted to investigate the effect of salinity and drought stress on water uptake reduction by maize. In order to exert this stresses, the pots were divided into two compartments including salinity and drought stresses. For two seasons, greenhouse experiments were conducted in a randomized design with four replicates in 2017. Water uptake by maize was measured daily in saline compartment of pots under constant matric potential of -100 cm, in different salinity levels of irrigation water (0, 1.7, 3.36, 6.33 and 8.35 dS m-1). The osmotic potential in pots was kept constant after the treatment initiation. The matric and osmotic potentials were quantified based on equal water uptake by roots in salinity and drought compartments of pots. In spring, the ratio of matric to osmotic potential was 0.28, 0.5, 0.47 and 0.46 in corresponding drought treatments (D1, D2, D3, D4)  and salinity treatments (S1, S2, S3, S4). For autumn, these ratios were 0.25, 0.32, 0.32 and 0.33 in corresponding drought treatments (D1, D2, D3, D4) and salinity treatments (S1, S2, S3, S4). Water uptake reduction by one unit decrease of matric potential was found to be more than the one caused by one unit decrease of osmotic potential. Osmotic potential had more effect than the matric potential on reducing root mass under the same water use conditions. These results indicated that the assumption of matric and osmotic potentials to be additive or multiplicative is not valid. The results of this study can be used to accurately manage irrigation water under salinity and drought stresses.