EFFECTS OF PHOTON FLUX-DENSITY ON PHOTOSYNTHESIS, GROWTH, FLOWERING, AND OIL CONTENT IN BORONIA

Boronia heterophylla is cultivated for cut flowers and B. megastigma f or volatile oil production. Both species are endemic to south-western Western Australia and their natural habitat is often shaded by a canop y of Melaleuca parviflora or Eucalyptus marginata. Shade tents were us ed to examine the influence of reduced photon flux density (PFD) on ph otosynthesis, growth, and flower production in B. heterophylla and B. megastigma. Volatile oil content was also examined in B. megastigma. P hotosynthesis in field-grown B. heterophylla was saturated at 16.2 mu mol CO2/m(2).s under a PFD of 1022 mu mol/m(2).s (75% full sunlight). Flower number was highest under 75% full sunlight but the number of ha rvestable stems was the same under 75% and full sunlight. More flowers were produced by B. megastigma plants grown under 75% full sunlight. Content of alpha-pinene and limonene decreased with decreasing light i ntensity, whereas beta-ionone and docecyl acetate increased with decre asing light intensity.