Timing of nitrogen application to macadamias. 2. Storage carbohydrates

Abstract

Samples of wood and bark were taken monthly from macadamia (Macadamia integrifolia Maiden and Betche) tree trunks and analysed for total 'fermentable' carbohydrates. Carbohydrates (%, w/w) were high during autumn-winter and declined to low levels in summer when oil was accumulating in kernels. Reproductive growth appeared to draw heavily on carbohydrate reserves. Vegetative growth, on the other hand, was not generally reflected in lower carbohydrate levels in tree trunks. Application of nitrogen (N) during summer resulted in higher carbohydrate levels than when applied in autumn or winter. Despite these differences, there was no apparent accumulation of carbohydrates in the months directly following application of N. The low N status of control trees was not reflected in low concentrations of storage carbohydrates. Wood tissues had a higher concentration of carbohydrates than bark, perhaps reflecting the sampling procedures used. Further work to quantify the contribution of storage carbohydrates and current photosynthesis to yield is justified.