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Feed the plant meat.

BACK IN 1878, Charles Darwin reported that when insectivorous sundew plants were denied insect prey they showed less vigorous growth, produced fewer flowers and set less seed than plants provided with insects. It is thought that carnivorous plants, often found on infertile acidic soils, with little competition from other plants, benefit from the nutrients in their prey.

Darwin, and more lately others, have hypothesised that the somewhat startling predatory behaviour of carnivorous plants should, therefore, prove more beneficial to plants growing in nutrient-poor soils than in fertile soils.

White some studies into various species have supported this view, others have not. Recently, scientists at the University of Western Sydney, Richard Jobson, Charles Morris and Shelley Burgin, conducted an experiment to determine whether the meat-eating bladderwort (Utricularia uliginosa), a rootless herb, responds to the presence or absence of prey, and to increased nitrogen when grown in pots.

This intriguing plant, found along the east coast of Australia and in South-east Asia, possesses small, spherical, water-filled traps or bladders that have a miniature trap-door and negative pressure within. If a very small invertebrate prey animal touches trigger hairs on the trap, the door is released and an influx of water carries the hapless victim into the bladder where it is `digested' by enzymes.

Jobson and his colleagues manipulated nitrogen levels (control plus two treatments) by adding ammonium nitrate to the pots containing the plants. They controlled the prey supply by adding either Euglena (a motile single-celled organism) atone or Euglena plus tiny invertebrate animals (copepods, nematode worms and the like), known collectively as meiofauna.

They concluded that trapping of small invertebrates (meiofauna), in combination with Euglena, definitely conferred a growth advantage. The benefit gained by trapping meiofauna lessened as nitrogen level increased, as hypothesised. Unexpectedly, at the lowest nitrogen level, trapping of Euglena depressed plant growth, apparently because it competed with the bladderwort for nitrogen under these conditions -- the prey here acting as a parasite.

On the whole, the researchers say their results indicate that bladderwort growth was not significantly affected by addition of nitrogen, but did benefit from carnivory. They suggest that, at tow nitrogen levels, the carnivorous tendencies of the bladderwort allow it to overcome a nitrogen deficiency, ironically induced by Euglena prey, and deficiencies of other nutrients when nitrogen is more plentiful in the soil substrate.

Jobson RW Morris EC and Burgin S (2000) Carnivory and nitrogen supply affect the growth of the bladderwort Utricularia uliginosa. Australian Journal of Botany, 48: 549-560.
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Title Annotation:effect of nitrogen supply on growth of carnivorous plants
Author:Davidson, Steve
Article Type:Brief Article
Geographic Code:8AUST
Date:Oct 1, 2000
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