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Characterization of Meadowfoam CO₂ Exchange Rates

Dep. of Crop and Soil Sci., Oregon State Univ., Corvallis, OR 97331-3002

Patrick J. Breen

Dep. o Horticulture, Oregon State Univ., Corvallis, OR 97331-3002

^* Corresponding author.

Recent evidence suggests that meadowfoam (Limnanthes alba Hartweg ex Benth.) seed-set and seed-fill may be limited by the availability of photoassimilates. Our objectives were to determine the CO₂ exchange rates (CER) of leaves (rosette and stem leaves), stems, and sepals of "Mermaid" meadowfoam in controlled environments, and to evaluate the variability in leaf net photosynthesis within and between field.grown selections. We used a semi-closed compensating system to measure the CER of different parts of potted plants in a controlled environment. We also measured net photosynthesis for single leaves of solid-stand or single-spaced plants of field-grown meadowfoam selections using a portable photosynthesis system. Net photosynthesis and respiration rates of Mermaid rosette leaves at vegetative stage averaged 19.2 and 4.0/µmol m^–2 s^–1, respectively. These values were similar to those for rosette leaves during early stem growth and the leaves on flowering stems. Net photosynthesis of rosette leaves during early flowering averaged only 7.9 µmol m^–2 s^–1. The CER of sepals was similar to that of leaves on flowering stems. Because most leaves senesce by mid flowering, the contribution of sepal photosynthesis to seed fill could be significant. The stem net photosynthesis during flowering on a per plant basis was only 7% of that for the sepals. Differences among field-grown selections for phytomass and seed production were not associated with their variations in net photosynthesis of single leaves measured instantaneously. Photosynthetic capacity of sepals and stems, however, may play a role in determining potential seed yield of meadowfoam.

Received for publication April 20, 1992.