Temporal patterns in mineral nutrient accumulation and allocation during macadamia nut fruit development

This study systematically analyzed the dynamic accumulation and allocation of dry matter and nutrients during fruit development in macadamia. The results demonstrated that fruit dry matter accumulation followed a single sigmoidal curve. A rapid growth phase occurred between 33 and 97 days after flowering (DAF), with dry weight increasing from 0.20 g fruit −1 to 6.48 g fruit −1 , reaching 8.48 g fruit −1 at maturity. Whole-fruit nutrient concentration gradually declined from 15 to 97 DAF and stabilized thereafter, with maturity sequence: K > N > P > Ca > Mg > Mn > Fe > B > Zn > Cu. Tissue-specific analysis revealed significantly higher concentrations of N, P, Mg, Zn, and B in the kernel compared to the husk/shell. The husk dominated K (88.63%) and Fe accumulation, while the shell was the primary reservoir for Cu and Mn. Whole-fruit nutrient accumulation exhibited sigmoidal growth, K was highest at maturity, followed by N, and exceptionally low P accumulation (only 9.34% of N). The micronutrient accumulation ranked Mn > Fe > B ≈ Zn > Cu. Cu, Mn, and B entered rapid accumulation earlier (40-44 DAF) than other nutrients (49-54 DAF) per logistic models. Nutrient allocation among fruit tissues exhibited spatiotemporal specificity: the kernel dominated N, P, Cu, Zn, and Fe accumulation from 97 to 142 DAF; the husk continuously accumulated K; and Ca, Mn, and B accumulation in the shell increased during development. This study first systematically reveals the nutrient demand characteristics during macadamia fruit development, particularly the exceptionally low P requirement in the fruit and the hyper-accumulation of K in the husk, providing a theoretical basis for precise K fertilization during expansion and timed macro/micronutrient management.