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NH 3 and NO 2 fluxes between beech trees and the atmosphere – correlation with climatic and physiological parameters
Author(s) -
GESSLER ARTHUR,
RIENKS MICHAEL,
RENNENBERG HEINZ
Publication year - 2000
Publication title -
new phytologist
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 3.742
H-Index - 244
eISSN - 1469-8137
pISSN - 0028-646X
DOI - 10.1046/j.1469-8137.2000.00712.x
Subject(s) - beech , stomatal conductance , fagus sylvatica , transpiration , atmosphere (unit) , relative humidity , compensation point , photosynthesis , humidity , flux (metallurgy) , chemistry , conductance , water vapor , atmospheric sciences , botany , analytical chemistry (journal) , environmental chemistry , meteorology , biology , physics , biochemistry , organic chemistry , condensed matter physics
The dynamic‐chamber technique was used to investigate the correlation between NH 3 and NO 2 fluxes and different climatic and physiological parameters: air temperature; relative air humidity; photosynthetic photon fluence rate; NH 3 and NO 2 concentrations; transpiration rate; leaf conductance for water vapour; and photosynthetic activity. The experiments were performed with twigs from the sun crown of mature beech trees ( Fagus sylvatica ) at a field site (Höglwald, Germany), and with 12‐wk‐old beech seedlings under controlled conditions. Both sets of experiments showed that NO 2 and NH 3 fluxes depended linearly on NO 2 and NH 3 concentration, respectively, in the concentration ranges representative for the field site studied, and on water‐vapour conductance as a measure for stomatal aperture. The NO 2 compensation point determined in the field studies (the atmospheric NO 2 concentration with no net NO 2 flux) was 1.8–1.9 nmol mol −1 . The NH 3 compensation point varied between 3.3 and 3.5 nmol mol −1 in the field experiments, and was 3.0 nmol mol −1 in the experiments under controlled conditions. The climatic factors T and PPFR were found to influence both NO 2 and NH 3 fluxes indirectly, by changing stomatal conductance. Whilst NO 2 flux showed a response to changing relative humidity that could be explained by altered stomatal conductance, increased NH 3 flux with increasing relative humidity (>50%) depended on other factors. The exchange of NO 2 between above‐ground parts of beech trees and the atmosphere could be explained exclusively by uptake or emission of NO 2 through the stomata, as indicated by the quotient between measured and predicted NO 2 conductance of approx. 1 under all environmental conditions examined. Neither internal mesophyll resistances nor additional sinks could be observed for adult trees or for beech seedlings. By contrast, the patterns of NH 3 flux could not be explained by an exclusive exchange of NH 3 through the stomata. Deposition into additional sinks on the leaf surface, as indicated by an increase in the quotient between measured and predicted NH 3 conductance, gained importance in high air humidity, when the stomata were closed or nearly closed and/or when atmospheric NH 3 concentrations were high. Although patterns of NH 3 gas exchange did not differ between different months or years at high NH 3 concentrations ( c . 140 nmol mol −1 ), it must be assumed that emission or deposition fluxes at low ambient NH 3 concentration (0.8 and 4.5 nmol mol −1 ) might vary significantly with time because of variation in the NH 3 compensation point.