Myrtle myth? Manuka makes more nectar on impoverished soils?

Noe S1, Clearwater M1, Manley-Harris M1, Richardson S2 and Whitehead D2

  1. University of Waikato, NZ.
  2. Landcare Research Manaaki Whenua, Lincoln, NZ.

It has been proposed that the extreme soil nutrient poverty and intense fire regime of Australia results in plants having excess carbon resources. They are still able to photosynthesise, but do not have the soil nutrients with which to combine the produced carbohydrates for nutrient rich tissue growth. This is hypothesised to have resulted in many Australian plants evolving unique, anomalous sinks for this extra carbon, as carbon rich compounds such as wood, oils, and nectar. The manuka plant (Leptospermum scoparium, Myrtaceae) occurs both in Australia and New Zealand, the nectar from its flower being the raw material for the production of the world-renowned manuka honey. Beekeepers have recounted that the best mānuka honey yields are from manuka growing on impoverished soils, suggesting manuka exhibits anomalously high nectar production on poor soils, possibly because of excess carbon. As yet there has been no thorough testing of this theory. This research investigates the effects of soil fertility on manuka growth, flowering, and nectar production, aiming to answer the question – does manuka make more nectar on impoverished soils? Potted manuka plants of two NZ provenances growing in an open field will be supplied with nutrient treatments testing the effects of soil nitrogen and phosphorus. Vegetative growth and photosynthesis; flowering timing, duration, and intensity; and nectar production will be monitored over two successive seasons. Examining the role of soil nutrient status in determining nectar flow for honey production purposes will improve our understanding of the highly variable nature of nectar production. The data generated from this research will contribute to a landscape scale model predicting nectar resources available through time for honey production.