Plant Responses to Individual and Combined Effects of Abiotic Stresses: Lycium depressum L. Vegetative Parameters under Salinity and Drought

Lycium depressum L. is the only native tree-like life-form species inhabited in saline and alkaline regions of Turkmen Sahra located at Golestan province in Northern Iran. During past years, efforts have been made to increase vegetation cover of the area by cultivation of L. depressum L. to reduce water and wind erosions and dust storm challenges; however, the cultivation of this species has not been quite successful. Regarding the importance role of L. depressum in the ecosystem, a greenhouse experiment was conducted in January 2018 with different levels of salinity and drought stresses. Salinity stress (control (4 dS/m), 14, 24, 34 and 44 dS/m) applying NaCl solution and drought stress (control (0), 0.25, 0.50, 0.75 and 1 MP) applying PEG 8000 as well as their combinations were conducted on plant cuttings (clones) using factorial experiment and Response Surface Method (RSM). Data were collected for leaf number (LN), root length (RL) and plant height (PH). Through the findings, it was concluded that drought stress had higher negative effect on plant function than salinity stress which dramatically reduced LN, RL and PH parameters (P<0.05). It was also inferred that combined treatments had higher negative effects on plant function than the individual treatments. Additionally, the result showed a significant difference between aerial organs and underground organs with regard to the severity of being affected by salinity and drought stresses so that LN and PH were highly affected comparing with RL. Generally, we observed that higher levels of salinity (higher than 30 dS/m) and drought (higher than 0.25 MP) will adversely affect the growth of plant organs leading to reduction of plant yield; even in some cases, it causes the plant total death. Finally, it was concluded that L. depressum is highly affected by drought rather than salinity.