Photosynthesis of meadowfoam leaves at various photon fluxes and CO 2 concentrations

Abstract

Meadowfoam ( Limnanthes alba Hartweg ex Benth.) is a new oilseed crop. Information regarding the effects of photosynthetic photon flux (PPF) and carbon dioxide concentration [CO 2] on net photosynthesis is important for understanding the potential capacity and the limitations of this crop to assimilate CO 2. Such information is useful for further improvement of meadowfoam seed and oil yield, as well as for growing this plant in controlled environments. The steady-state CO 2 exchange rates (CER; leaf area basis) of Mermaid meadowfoam ( L. alba subsp. alba) leaves were measured in a semi-closed compensating system at various PPF and [CO 2]. Measurements were made on rosette leaves of controlled environment-grown plants during vegetative growth, early stem elongation and early flowering. At all stages of development, CER responded hyperbolically to PPF and reached near saturation at a PPF of about 900 μmol m −2 s −1 when [CO 2] was 340 μl l −1. At saturating PPF, leaf CER was 18 μmol m −2 s −1 during the vegetative stage, 15 μmol m −2 s −1 at early stem elongation and 8 μmol m −2 s −1 at early flowering. The apparent quantum yield (mole CER per mole PPF at leaf surface) determined at low PPF when the response curve was linear was the same during vegetative and early stem elongation. The 99% confidence intervals for the apparent quantum yield of these plants were 0.038 and 0.046. The 99% confidence intervals for light compensation point during these stages were 63 and 79 μmol m −2 s −1. During both vegetative and early stem elongation stages, the CER increased sharply as [CO 2] increased (PPF=1200 μmol m −2 s −1) and reached a plateau near 650 μl l −1 CO 2. At this saturating [CO 2], the CER was 45 μmol m −2 s −1 during the vegetative stage and 33 μmol m −2 s −1 during early stem elongation. The [CO 2] compensation point measured transiently on four plants during vegetative stage was 74±5 μl l −1. The photosynthetic rate and efficiency of L. alba were similar to those for cool-season C 3 grasses.