Effect of Water Stress on Gas Exchange in Fronds of the Ostrich Fern (Matteuccia struthiopteris(L.) Todaro)

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Abstract
Experiments were conducted in a gas exchange system to examine the effect of a water stress, induced by −200 kPa polyethylene glycol (PEG), on carbon dioxide and water vapour flux, frond diffusive resistance, intercellular carbon dioxide concentration, carbon dioxide residual resistance and frond water potential in the ostrich fern (Matteuccia struthiopteris (L.) Todaro). Measurements were taken 1 d after the application of PEG. The measurements were made on young fronds (8 d old) and mature fronds (20–24 d old) at PPFD's (Photosynthetic Photon Flux Density) from 0–1400 μmol m−22 s−1. Water stress decreased the net photosynthesis rate in mature fronds at PPFD's of 210 μmol m−2 s−1 or greater and increased the net photosynthesis rate below 210 μmol m−2 s−1 in young fronds. The increase in net photosynthesis in stressed young fronds was associated with a significant reduction in the dark respiration rate. Water stress and decreasing PPFD's increased frond diffusive resistance. Carbon dioxide concentration in the intercellular spaces decreased with increasing frond age and PPFD's up to 200 μmol m−2 s−1. The residual resistance to carbon dioxide flux was not significantly affected by either frond age or water stress. Frond water potential was significantly lower in mature fronds than in young fronds.