High-Zn wheat alleviates P-Zn antagonism by improving Zn activation, acquisition, and translocation at key growth stages

Context or problem: Application of phosphorus (P) fertilizer has achieved a remarkable increase in yield but has also resulted in decreased zinc (Zn) concentration and its bioavailability in cereal grains.Objectives: Selecting, breeding, and understanding the mechanism for wheat cultivars with high-yield and highgrain Zn under P application is urgent and difficult, with the purpose of alleviating PZn antagonism and solving Zn malnutrition globally.Methods: In a five-year field experiment on the southern Loess Plateau, China, selected high-yield wheat cultivars with contrasting grain Zn concentrations were assessed for rhizosphere Zn activation, root Zn acquisition, and Zn translocation among plant parts at the key growth stages under different P fertilization rates.Results: Results showed that although the grain Zn concentration decreased with P application, it decreased less and still remained around 49-65 mg/kg in the grain of high Zn (HZn) cultivars. This was 58-72% higher than that of the low Zn (LZn) cultivars on soil with 2.7 mg/kg Olsen-P and 0.55 mg/kg DTPA-Zn due to 32.9-55.4% higher shoot Zn uptake in HZn cultivars at harvest. P application enhanced the rhizosphere Zn activation of HZn cultivars by 21.6% higher than that of LZn cultivars at the jointing stage. However, P application inhibited the root Zn acquisition of both types of cultivars, except for that of the HZn cultivars at the anthesis. The Zn translocation from root to shoot was remarkably enhanced at the grain-filling stage, but much more for HZn cultivars with P application, with the transfer factor being 154% for HZn cultivars and 7.9% for LZn cultivars, respectively. Conclusions: Therefore, HZn cultivars alleviated the P-Zn antagonism and achieved higher grain Zn concentration than the recommended target of 40-60 mg/kg, by maintaining higher rhizosphere Zn activation at the jointing stage, stable high Zn acquisition at the anthesis, and higher Zn translocation capacity from root to shoot during the grain-filling stage. Implications: Breeding and selecting cultivars with excellent acquisition performance and translocation capacity for Zn, accompanied by relatively lower soil available P and reasonable P application, may be an applicable Zn biofortification strategy for wheat and other cereals, overcoming the P-Zn antagonism.