Amino acid-chelated zinc application enhances sugar beet growth performance in carbonate alkaline soil by optimizing rhizosphere zinc speciation and microbial community structure

The low availability of zinc (Zn) in saline-alkali soils severely constrains crop productivity. Although sugar beet ( Beta vulgaris L.) is a halophytic and zinc-responsive crop, the efficacy and underlying mechanisms of novel zinc fertilizers in promoting its production within saline-alkali environments remain elucidated. In this study, a pot experiment was conducted to evaluate the effects of distinct zinc formulations—zinc sulfate heptahydrate, nano‑zinc oxide, and amino acid-chelated zinc—on sugar beet seedling growth in carbonate-alkali soil. We analyzed plant Zn accumulation, Zn fractionation, and the biochemical characteristics of the rhizosphere soil. The results demonstrated that amino acid-chelated zinc (AZn) exhibited superior efficacy compared to other treatments. Specifically, AZn application significantly modulated soil Zn fractions, increasing the exchangeable Zn (71.93%) and organically bound Zn (29.82%) fractions, while concurrently decreasing the carbonate-bound Zn (58.95%) and residual Zn (5.62%) fractions. Concurrently, specific beneficial functional bacteria, notably Microvirga, were enriched, thereby enhancing microbial nitrogen fixation potential and increasing the complexity of the co-occurrence network. This synergistic effect—stemming from the optimization of zinc speciation and the amelioration of the microbial community—established a positive feedback loop within the plant-soil-microbe system. This loop facilitated the translocation of zinc to aboveground tissues (increasing the translocation factor by 16.47%), markedly elevated soil available zinc levels (by 295.25%) and plant zinc accumulation (by 332.31%), and ultimately significantly promoted sugar beet growth (increasing dry weight by 257.14%). This study confirms that AZn can alleviate saline-alkali stress by remodeling the rhizosphere habitat, providing a theoretical basis for the scientific application of zinc fertilizers in saline-alkali soils.