Effect of frond age on frond elongation, gas exchange, and water relations in the ostrich fern (Matteuccia struthiopteris)

The effect of frond age in the ostrich fern (Matteuccia struthiopteris) upon changes in frond elongation, frond water status (osmotic, pressure, and total water potential), and gas exchange (diffusive resistance, net photosynthesis rate, and dark respiration rate) was examined. The maximum elongation rate in the youngest fronds was 2.83 mm h−1 and occurred between 1500 and 2100 hours. Growth of individual fronds was completed in ca. 16–20 days after emergence from the apical bud. As a frond approached final length, both the dark respiration rate and rate of daily elongation decreased. Compared with mature fronds, young fronds (5 to 8 days old) had higher dark respiration rates and lower net photosynthesis rates. They also had higher osmotic potentials and lower pressure potentials and predawn diffusive resistances. In the youngest fronds (3 and 6 days old) the fastest elongation rates occurred at the lowest water potentials. This phenomenon may be an example of "growth-induced water potential." The increase in pressure potential and decrease in osmotic potential as the frond approached full expansion on day 16 indicates an "apparent" osmotic adjustment which was probably due to a decrease in the yielding properties of the cell walls while solutes continued to accumulate in the tissue. At full expansion further accumulation appeared to stop, suggesting that the frond had increased net solute export.