Impact of ZnSO₄ and ZnEDTA applications on wheat Zn biofortification, soil Zn fractions and bacterial community: Significance for public health and agroecological environment

Application of Zn fertilizer can improve cereal Zn concentration, and affect soil microbial ecology by increasing soil Zn concentration. We investigated the effects of three-year continuous applications of different Zn fertilizers (i.e., ZnSO₄ and ZnEDTA) on wheat Zn biofortification, soil Zn fractions and bacterial community on a Zn deficient calcareous soil. The results showed that ZnEDTA application induced a higher grain Zn concentration and bioavailability than those in the case of ZnSO₄ application, which met the target of wheat Zn biofortification within three years. Correspondingly, ZnEDTA application resulted in a higher Zn availability in soil than ZnSO₄ application by facilitating Zn transformation into exchangeable and organic matter loosely bound fractions. Bacterial diversity and richness were not affected, but the bacterial community was altered after three years Zn applications. ZnEDTA application significantly decreased the relative abundances of Nocardioides, Arthrobacter, Blastococcus, Gemmatimonas, and Streptomyces as compared with ZnSO₄ application. Meanwhile, ZnEDTA application lowered α-glucosidase, β-glucosidase, and β-xylosidase activities in soil as compared with ZnSO₄ application. These results indicated that ZnEDTA application is an effective practice to achieve wheat Zn biofortification, but attention needs to be paid to the potential environmental risks associated with the decreased activities of microbes and enzymes in soil.