23 - Watering regime and photosynthetic performance of Gunnera tinctoria (Molina) Mirbel.  pp. 247-255

Watering regime and photosynthetic performance of <i>Gunnera tinctoria</i> (Molina) Mirbel.

By G. J. Campbell and B. A. Osborne

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SUMMARY

The influence of water status on photosynthesis and productivity of Gunnera tinctoria (Molina) Mirbel. was examined under natural conditions in an experimental garden in Dublin under two contrasting watering regimes. Application of water in amounts that simulated the rainfall conditions of the west of Ireland produced large increases in productivity although there were only small effects on instantaneous rates of net photosynthesis. The lack of a correlation between photosynthetic rate and biomass accumulation is considered. Stomatal conductance was often highest in the morning and subsequently declined throughout the day, irrespective of watering regimes, indicating possible limitations in water transport from the root to the shoot even when plants were supplied with additional water. The significance of these results for a plant restricted to wet, humid environments is discussed.

INTRODUCTION

The recent habitats occupied by the genus Gunnera L. are characterised by high rainfall, high humidity conditions in which low temperatures are rare (Osborne et al., 1991; Palkovic, 1974). The global distribution of the genus is also thought to have been more extensive in the past but has decreased dramatically due to a reduction in annual levels of precipitation and an increase in seasonal temperature variation (Osborne et al., 1991; Jarzen, 1980).

Gunnera tinctoria (Molina) Mirbel was introduced into Ireland about 100 years ago as an ornamental shrub and is now naturalised in westernmost regions of the country (Campbell & Osborne, 1990) in areas of high annual rainfall (> 1600 mm) and high humidity not unlike its tropical and sub-tropical habitats where rainfall approaches 2000 mm per year (Müller, 1982; Osborne, 1989).