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Organic acids in root exudates and soil solutions. Importance to calcicole and calcifuge behaviour of plants.

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Author

Summary, in English

Many vascular plant species are unable to colonise calcareous sites, the floristic composition of adjacent limestone and acid silicate soils differing markedly. The inability of these 'calcifuge' species to establish themselves and grow on limestone soil appears to mainly be related to their low capacity for solubilising and absorbing phosphate and/or iron from such soils. Differences between calcifuge and calcicole species (the latter normally growing on calcareous soil) in their root exudation of low-molecular organic acids (LOAs) can lead to their ability to solubilise mineral nutrients from the soil differing. In the studies presented in this thesis I examined exudation by many calcicole and calcifuge species. Exudation was studied for plants grown hydroponically, for germinating seeds and seedlings and for plants grown in a pH intermediate soil. I found that calcicole species generally have a higher, often much higher, exudation rate of dicarboxylic oxalate and tricarboxylic citrate than calcifuge species do. These two LOAs were also shown to have a strong solubilising effect on soil phosphate and iron, both in calcareous and silicate soil. I also studied the calcifuge behaviour of Rumex acetosella in greater detail. R. acetosella was found to be a highly phosphate-limited species, its growth being closely correlated to the amount of easily exchangeable phosphate in the soil. This species, which contain large amounts of oxalate in its leaves, appears in any case to lack the ability to increase the exudation rate of LOAs in response to phosphate limitation. In my thesis I propose that high exudation rates of dicarboxylic and tricarboxylic organic acids is one of the mechanisms explaining calcifuge behaviour in plants. I also propose that high root exudation rates of LOAs from plants can be an adaptation to nutrient limiting conditions in soils.

Publishing year

1998

Language

English

Document type

Dissertation

Publisher

Department of Ecology, Lund University

Topic

  • Ecology

Keywords

  • nutrient-solubilisation
  • iron
  • phosphate
  • nutrient-limitations
  • citrate
  • oxalate
  • organic acids
  • root exudation
  • acidifuge
  • Calcicole
  • calcifuge
  • adaptations.
  • Plant ecology
  • Växtekologi

Status

Published

Supervisor

  • [unknown] [unknown]

ISBN/ISSN/Other

  • ISBN: ISBN 91-7105-106-6
  • ISRN: SE-LUNBDS/NBBE-98/1050/+108

Defence date

13 November 1998

Defence time

10:00

Defence place

Blå Hallen, Ecology Building, Sölvegatan 37

Opponent

  • John A Lee (Prof)