A unifying principle linking water uptake and nutrient delivery in trees with implications for soilless vascular delivery

Tree productivity, orchard sustainability and dryland reforestation are constrained simultaneously by water scarcity and nutrient losses. Here a unifying nutrient-water principle is developed for woody plants. The principle states that the minimum soil-derived flow compatible with a specified plant state is the greater of a hydraulic baseline and the flow needed to deliver the limiting nutrient. For nutrient i , internal delivery is represented locally as J i = η i C i Q s + I i , where C i is effective root-zone concentration, Q s is soil-derived flow, η i is an effective soil-to-xylem transfer coefficient and I i is direct vascular input. The formulation predicts a hyperbolic decline in nutrient-driven flow requirement with increasing balanced nutrient concentration, control by the most limiting nutrient and strong leverage from efficient delivery when soil losses are high. Controlled split-root and hydroponic studies demonstrate rapid nutrient-hydraulic coupling, while ecosystem, tree and orchard observations are consistent with the predicted importance of nutrient balance. Published injection studies support targeted vascular correction of selected nutrient deficiencies and provide a basis for evaluating broader soilless delivery. The principle links plant hydraulics and mineral nutrition in a concise, quantitative and testable framework and identifies experiments needed to determine its parameters and practical limits.