Effect of nitrogen source on bean growth under water deficit conditions

Abstract

The study investigated the effects of inorganic nitrogen on some physiological and biochemical traits of beans under water deficit stress. The experiment was arranged in factorial order based on completely randomized design with three replications in the greenhouse. Treatments included irrigation regimes at 30%, 55% and 80% of field capacity and different nitrogen sources as control or relying on nitrogen fixation, NH4+, NO3- and NH4++NO3-. Chlorophyll a and b, total chlorophyll, and carotenoid content decreased as a result of water stress. NO3- led to higher chlorophyll a and total chlorophyll content compared with other nitrogen sources, while NH4+ consumption increased chlorophyll b and carotenoid content. Enhancing water stress reduced leaf soluble protein content and increased the amount of soluble sugars. Changes in initial fluorescence (Fo) increased over time, but the maximum fluorescence (Fm) and variable fluorescence (Fv) decreased. The photochemical efficiency of photosystem II (Fv/Fm) decreased due to water deficit. Biomass and shoot length were reduced by increasing stress severity. Among treatments of nitrogen sources, NO3- significantly increased shoot dry weight. The lowest shoot dry weight was obtained in the nitrogen-fixing (control) plants.