Physiological, Biochemical and Morphological Tolerance Mechanisms of Faba Bean (Vicia fabaL.) to the Combined Stress of Water Deficit and Phosphorus Limitation

Water deficit and phosphorus (P) deficiency are among the most severe factors limiting agricultural productivity. In this study, two contrasting faba bean (Vicia faba L.) varieties for their response to water deficit were used to identify some agro-physiological and biochemical traits involved in the tolerance mechanisms to combined water deficit and P limitation. Plants were grown under greenhouse conditions in agronomic soil, under two P levels: 10.4 mg P kg−1 (deficient) and 30.4 mg P kg−1 (sufficient), and two watering regimes: 40% of soil field capacity (FC; water deficit) against 80% FC (control). We hypothesis that P fertilization improves the tolerance of faba bean plants and their symbiosis to water deficit. The results demonstrated that water deficit and P-deficiency treatments applied separately or combined reduced substantially plant biomass, leaf water parameters, and nitrate reductase activity. Similarly, nutrients concentrations were significantly reduced under P-deficiency, while sufficient P-conditions significantly increased their uptake under water deficit. The tolerance was positively correlated to the ability of plants to overcome the combined stressors by inducing phosphatase activity, accumulating glycine betaine and activation of antioxidant enzymes and also by maintaining cell membrane stability. The findings suggest that the combination of the two stresses alter more the plant metabolisms compared to individual stress, with Reina Mora being the most affected by the applied stressors. Likewise, P fertilization is a relevant approach to overcome some effects of water deficit.