Changes morphological, agronomic and oil and essential oil content in Purslane (Portulaca oleracea L.) under drought stress, mycorrhiza and organic / chemical fertilizer of nitrogen

Water and nitrogen are among the key factors determining the yield of agricultural production around the world. Iran is dominated by arid and semiarid climate, with water availability presenting a great problem in many areas across the country. Water stress have altered plants’ metabolism significantly, thereby attenuating the growth, photosynthesis, and ultimately yield of the plants. Accordingly, it is very important to identify the mechanisms through the plant adapts to various conditions and resists against stresses, and to understand possible ways to address such stresses. In addition, under such conditions, drought management is an essential necessity. Cultivating plants with lower water requirements is a solution for effective management of available water resources. Being largely adaptable to a wide spectrum of various weather conditions, purslane serve as an economically efficient product (both as vegetable and medicinal plant) in terms of water scarcity. Furthermore, in order to effectively manage water consumption in agriculture, adoption of various farming techniques, such as application of organic fertilizers or improving biological conditions of soil may render effective for reducing the impacts of water stress, while less use of chemical fertilizers may add to agricultural sustainability and health of medicinal plant.   In order to investigate the effect of combining different sources of nitrogen fertilizer (organic and chemical fertilizers) and mycorrhiza under drought stress on morphological and agronomic properties and also on Essential oil and oil contents of purslane leaves, experiments were performed in Zavariyan Village, Qom Province, Iran during 2015-2016, in the form of, factorial split plot in the base of randomized complete blocks and three replications. Factors include two water deficit stress (I1 without stress: irrigation time is when the amount of available water for plants on farm is 70% FC; I2 stress: irrigation time is when the amount of available water for plants on farm is 50% FC.) and two treatments mycorrhizal M1 inoculated and M2 non-inoculated with the fungus, as treatments the main factor and six sources of fertilizers, mixture of organic fertilizers (sheep and chicken) and chemical fertilizers including: (F1 without the use of organic fertilizers and chemical fertilizer, F2 including 100% organic fertilizers without the use of chemical fertilizers, F3 including 75% organic fertilizers and 25% chemical fertilizers, F4 including 50% organic fertilizers and 50% chemical fertilizers, F5 including 25% organic fertilizers and 75% chemical fertilizers, F6 without the use of organic fertilizers and 100% chemical fertilizers) as the sub factors.   Results indicated that, during the first and second years of the experiment, drought stress reduced the height (13.8% and 16.4%), Mycorrhizal colonization (30.3% and 15.3%), phosphorus content of leaves (5.8% and 7.7%), Biological yield (21.3% and 17.7%), grain yield (22.5% and 21.1%), and total antioxidant capacity of the leaves (15.9% and 10.5%) of purslane. At the same time, production of secondary and medicinal metabolites (essential oil (6.2% and 5.4%) and oil concentration (48.7% and 57.9%) on the leaves of purslane increased. Application of mycorrhiza led to an increase in all of the considered properties due to its larger capacity for absorbing water and nutrients (phosphorous, in particular) and attenuating negative impacts of drought stress. The results also indicate that, maximum values of most of the considered properties in the treatments without stress were observed by mycorrhizal application and combined fertilizer (organic and chemical).   To sum up, it can be concluded that, if the aim of planting purslane is to use its growth and seed parts, the best results can be achieved upon adequately irrigating the plant while applying mycorrhiza and mixed nutrient system (50% organic fertilizers + 50% chemical fertilizers). However, should medicinal and qualitative aspects of the plant are concerned, drought stress treatment with mixed nutrient system (25% organic fertilizers + 75% chemical fertilizers) represent the most suitable treatment for enhancing secondary metabolites under stress conditions, highlighting the role of nitrogen as an essential element in the structure of the plant essential oil.