Low efficiency of Zn uptake and translocation in plants provide poor micronutrient enrichment in rice and soybean grains

Abstract

Recent research has shown the need for an in-depth knowledge of zinc biofortification of cereal and oilseed grains due to its importance to human nutrition. However, little is known about the Zn dynamics in plant–soil system. In this work, we evaluated the effect of soil-applied Zn on the absorption, translocation, and compartmentalization of Zn in rice (Oryza sativa L.) and soybean (Glycine max L. Merrill) plants. The soil used in the greenhouse experiment was fertilized with zinc chloride (ZnCl2) at rates of 0, 1, 2, 4, and 8 mg Zn kg−1. The source of Zn was labeled by 65Zn with specific activity of 185.5 kBq mg−1 Zn. The amount of Zn derived from fertilizer and its use in each plants compartment was determined by direct method in isotopic calculations. Rice and soybean plants presented low efficiency in the absorption from soil-applied Zn. The accumulated Zn in the panicle, pod, and grains was not modified, due to its low translocation in the plant. The Zn uptake in rice plants was from 1.34 to 4.60 mg pot−1 in shoots and just 0.81 to 1.43 mg pot−1 translocated to panicles. Soybean plants presented Zn uptake between 2.36 and 4.68 mg pot−1 in shoots, out of which 0.19 to 0.34 mg.pot−1 and 0.48 to 0.57 mg pot−1 translocated to grains and pods, respectively. The nutrient utilization from fertilizer was low, with mean values of 12 and 8.7% for rice and soybean plants, respectively. Soil-applied Zn showed low capacity for enriching rice panicle and soybean pod or grain probably due low Zn uptake and translocation.