Seasonal variation in nutrient status of Australian waxflowers

Seasonal fluctuations in the concentrations of 12 nutrients were assessed over 3 years for Chamelaucium uncinatum cultivars Alba and Purple Pride and for Chamelaucium hybrid (C. floriferum x C uncinatum) known locally as Walpole wax. The plantings were located in the Mount Lofty Ranges, Lower South East and Lower Murray regions of South Australia. Tips of stems, 25-40mm long, were collected on a monthly basis. The nutrient data were used to identify the most suitable time for tissue analysis; to determine the magnitude of the differences in nutrient composition between cultivars; and to determine the correlations between nutrients. The effect of the sampling error was also determined. The seasonal decrease in concentrations of nitrogen (N), phosphorus (P), potassium (K), magnesium (Mg), and sulfur (S) corresponded with vegetative flushing (growth dilution effect). Concentrations of the variably mobile nutrients copper (Cu) and zinc (Zn) were unstable, particularly during autumn-winter. Concentrations of phloem immobile nutrients calcium (Ca), boron (B), and manganese (Mn) decreased early in the season, were lowest when vegetative flushing peaked (summer), and tended to increase in autumn and winter. For preferred sampling times, seasonal trends showed that concentrations of N, P, Ca, Mg, sodium (Na), chloride (Cl), B, Zn, and Mn were fairly stable over the period January-March. Similarly, concentrations of K, S, and Cu were relatively stable during the period July-September when vegetative growth was minimal. The error associated with our sampling procedure was within acceptable limits (coefficients of variation <10%) for N, P, K, Ca, Mg, Na, Cl, S, B, and Mn. For the cultivar Alba, the seasonal trends for all nutrients were similar even though they were grown at different sites. Nitrogen and Mg concentrations in stem tips of the cultivar Alba were consistently higher than those in stem tips of the cultivar Purple Pride. In contrast, concentrations of K, Na, Cl, and Mn were lower. For these nutrients, different interpretation standards may be required for these cultivars. Significant (P<0.05) correlations were found between many nutrients. For example, K concentrations were positively correlated with Cl, S, Cu, and Zn and negatively correlated with Ca and Mg concentrations. These significant relationships may indicate synergistic and antagonistic interactions between nutrients, which need to be considered when interpreting plant test data.