Interaction Effects of Fertilizers and Drought Stress on Morpho-Physiological Characteristics and Yield of Oenothera biennis L

To improve crops productivity under drought stress conditions, not only proper management of inputs in time, amount and form, but also the understanding of important physiological processes and defense mechanisms are required to avoid drought stress. Most plant species have the ability to form a symbiosis relationship with the Arbuscular mycorrhizal fungi. AMF could increase growth and yield of plants under water stress, and it is one of the most important biological fertilizers which can be used in mycorrhizal and Azospirillum fields. Research results have shown that mycorrhizal and Azospirillum fungi can moderate the adverse effects of drought stress in plants. One of the most important effects in terms of drought stress is changing the levels of some hormones in plant such as acetic acid and indole acetic acid. Other effects are direct absorption of water by fungal hyphae in soil and its transfer to the host plant, increasing leaf gas exchange, photosynthesis rate as well as enhance the activity of antioxidant enzymes in corn, excellent nitrate and phosphorus assimilation. In addition, extend the water absorption by increasing the leaf water hydration, leaf photosynthesis activity, osmotic regulation and changes in cell membrane flexibility. Hence, the current study was aimed to evaluate chemical fertilizers (nitrogen + phosphorus) and biological fertilizers (Azospirillum and mycorrhizal fungi) effects on water deficit stress on morpho-physiological traits and yield of evening primrose at different experimental stations (Tehran and Varamin regions).

Two experiments were conducted at two experimental stations in Tehran and Varamin in 2014 and 2015. Experiments were conducted in a split factorial layout within a randomized complete block design with three replications. Three irrigation regime treatments (IR 50 % FC, IR 40 % FC and IR 30 % FC; 50, 40 and 30 percent of field capacity) were randomized to the main plots. Subplots were consisted of factorial combinations of three chemical fertilizers (CF 0, CF 50 % and CF 100 %: no-application, 50 and 100 percent of nitrogen + phosphorus needed by plant) as well as four biological fertilizers (“-M and –Az” and “+M and +Az”: non-inoculated and inoculated with mycorrhizal and Azospirillum).

Water stress (moderate and severe) reduced plant height, shoot dry weight, leaf area index, seed yield, phosphorus content and relative water content. However, the highest water use efficiency was obtained at moderate water deficit stress. In addition, the highest root dry weight, root ratio shoot dry weight and catalase were obtained at severe water deficit stress. The application of chemical fertilizers and biological fertilizers in all cases mitigated the negative effects of water deficit stress on plant height, shoot dry weight, root dry weight, root ratio shoot dry weight, leaf area index, seed yield, phosphorus content, catalase, relative water content and water use efficiency traits. Water use efficiency of evening primrose increased with moderate water deficit, application of chemical (Nitrogen + Phosphorus) and biological (mycorrhizal fungi and Azospirillum) fertilizers.

 The compelling results of this study revealed that the inoculation mycorrhizal and Azospirillum could improve evening primrose growth under water deficit stress. Results showed that the application of biological fertilizers can improve evening primrose growth under drought stress. Moreover, mycorrhiza symbioses can increase absorption of moisture and nutrients, reduced irrigation requirements, enhancement drought resistance, more access to food in new places, production of thinner roots, increase root length and nitrogen fixation, which lead to reduction of drought detrimental effects.