Soil Zn Fertilization and Inoculation with Arbuscular Mycorrhizal Fungus and Azotobacter Chroococcum Bacteria Affect the Cd Concentration and Zn Bioavailability in Bread Wheat Grown in a Cd-spiked Soil

Abstract

ABSTRACT Wheat is the main staple crop in Iran and thus of critical importance in human nutrition. This study was conducted to investigate the effect of individual and co-inoculation of azotobacter chroococcum bacteria (A. chroococcum) and a species (Rhizophagus irregularis) of arbuscular mycorrhizal fungi (AMF) on improving the nutritional quality of bread wheat grain. We performed a pot experiment, in which the effects of R. irregularis and A. chroococcum inoculation, and zinc (Zn) fertilization [0, 4.4, and 8.8 mg (kg)−1] to cadmium (Cd)-spiked soil on increasing the Zn bioavailability and reducing the Cd concentration of wheat grains were tested. Inoculation with A. chroococcum increased the rate of root colonization by R. irregularis. Root colonization with AM fungus significantly reduced the grain Cd concentration especially after co-inoculation with A. chroococcum and soil application of ZnSO4 fertilizer. Mycorrhized plants, compared to non-mycorrhized plants had considerably higher grain concentrations of phosphorous (P) and nitrogen (N), which were affected by the application rate of ZnSO4 and co-inoculation with A. chroococcum. The response of grain Zn concentration to mycorrhization was dependent on the rate of Zn fertilization and inoculation with A. chorococum. Single inoculation with R. irregularis increased the concentration of phytic acid (PA) and also the molar ratio of PA:Zn in grains, which may have resulted in reduced Zn bioavailability. In contrast, double inoculation of plants with R. irregularis and A. chroococcum reduced the molar ratio of PA:Zn especially after application of ZnSO4. This study suggests that dual inoculation of wheat plants with A. chroococcum and R. irregularis together with Zn fertilization may enhance the nutritional quality of wheat grains.