Zinc in Soil–Plant–Human Systems: A Synthesis of Its Fate, Essential Roles, and Health Implications

Zinc (Zn) is an essential micronutrient that plays a pivotal role in the soil-plant-human continuum, influencing soil health, crop productivity, and human nutrition. Its behavior in soil is governed by a complex interplay of physicochemical and biological factors, including soil pH, organic matter, clay content, redox conditions, and environmental variability. Zn availability typically decreases in alkaline, calcareous, and sandy soils, whereas its solubility increases markedly with decreasing pH, resulting in a 100-fold decrease per unit decline. Organic matter exerts a dual influence by stabilizing Zn through complexation while also enhancing its mobility via soluble organometallic forms. Processes such as adsorption and desorption regulate Zn partitioning between the solid and solution phases of soil, thereby controlling its bioavailability and plant uptake. Zn plays essential roles in plant metabolism, including enzyme activation, membrane stabilization, and growth regulation, and contributes to human health by supporting immune function, endocrine regulation, and metabolic homeostasis. However, Zn imbalance remains a key challenge, as both Zn deficiency and excessive accumulation can adversely affect plant performance and human health, leading to impaired metabolism, oxidative stress, and micronutrient interactions. Furthermore, climate change is expected to alter Zn dynamics in soils, influencing its mobility, bioavailability, and transfer across trophic systems. This review provides a comprehensive, integrative synthesis of Zn dynamics across interconnected systems and highlights future research directions, emphasizing the need for integrated strategies that combine soil management, microbial interventions, crop improvement, and precision agriculture to increase Zn use efficiency and ensure sustainable agricultural and nutritional security.