Contrasting mineral allocation in deciduous almond and evergreen olive shapes interannual nutritional storage...

Mineral reserves in perennial tree organs buffer crop nutrition across seasons, but their magnitude and location vary among species. We hypothesized that deciduous almond, constrained to a narrow growing season, would commit to building large mineral reserves in perennial organs. In contrast, evergreen olive, able to take up minerals year-round, would rely on continuous uptake. We grew deciduous almond and evergreen olive trees under a range of nitrogen (N, 10-150 mg L^-1), phosphorus (P, 1-15 mg L^-1), and potassium (K, 10-150 mg L^-1) mineral concentrations in the irrigation water and monitored seasonal mineral composition in roots, wood, and leaves. Trees were later destructively harvested to determine organ biomass and mineral mass. Almond and olive differed in their mineral allocation (Fig. 8 - graphical abstract). Almond leaf concentrations stabilized after peak vegetative growth, whereas olive leaves accumulated minerals continuously. Almond fruit concentrations were elastic across the mineral application range. Almond leaf concentrations were largely insensitive to mineral application. Olive root and leaf concentrations increased across the tested range. Almond biomass peaked, then declined at high N. Olive biomass scaled continuously with mineral application. Whole-tree mass balance revealed mineral reserves equivalent to up to 1.5 years of annual removal in almond, where most of the reserve turns over via senescence. In contrast, in olive, minerals accumulate in the roots and leaves up to 10 seasons, contradicting our initial hypothesis. Leaf mineral concentration reliably classified a tree's mineral status in olive, but only for K in almond. Precise almond fertilization may therefore require whole-tree mass-balance approaches rather than leaf diagnostics.