Temporal Accumulation and Partitioning of Mineral Nutrients in Developing Macadamia Fruit

Abstract

This study quantified nutrient accumulation and partitioning among the kernel, shell, husk, rachis, and leaves during fruit development in three macadamia cultivars. Racemes and leaves were sampled at biweekly intervals until kernel maturity. The shell and rachis ceased to accumulate biomass earlier in the season than the husk or kernel. Nitrogen (N) and potassium (K) were the dominant nutrients accumulated in the fruit. Despite declining concentrations between 80 and 140 DAF, total kernel nutrient content continued to increase, indicating sustained nutrient import during this critical period. The kernel was the primary sink for N, phosphorus (P), sulfur (S), and magnesium (Mg), with peak accumulation occurring during rapid kernel growth at 80–175 days after flowering (DAF). In contrast, the accumulation of calcium (Ca) and manganese (Mn) into the kernel ceased earlier, suggesting limited late-stage mobility. The husk accumulated more K than the kernel and remained an active sink for K, S, Mg, Ca, and Mn until maturity, while N, P, and boron (B) accumulation slowed after ~107 DAF. The shell contributed minimally to nutrient demand, with N, zinc (Zn), and B accumulation ceasing after shell hardening (90–110 DAF). The cultivars exhibited consistent temporal patterns, differing mainly in magnitude. Nutrient partitioning efficiency among-the fruit components was highest for cv. A38. The rachis acted as a transient sink early in development before declining in mobile nutrients, while leaf nutrient dynamics did not reflect fruit demand.