On the gaseous exchange of ammonia between leaves and the environment

Determination of the ammonia compensation point.

Graeme Farquhar, Peter Firth, Rob Wetselaar, B Weir

Research output: Contribution to journalArticle


Whole shoots of Phaseolus vulgaris L. and other species were exposed to a range of partial pressures of gaseous ammonia in air and the resulting fluxes were measured. Net uptake is linear with partial pressure in the range 5 to 50 nanobars and is zero at a finite partial pressure, termed the ammonia compensation point. Below the compensation point, ammonia (or possibly other volatile amines) is evolved by the leaves. The compensation points in several species are near the low partial pressures found in unpolluted air and approximate to the Km of glutamine synthetase in vitro. In P. vulgaris L., the compensation point increases with temperature.
Original languageEnglish
Pages (from-to)710 - 714
Number of pages5
JournalPlant Physiology
Issue number4
Publication statusPublished - 1980
Externally publishedYes


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