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Comparative ecophysiology of CAM and C 3 bromeliads. II. Field measurements of gas exchange of CAM bromeliads in the humid tropics
Author(s) -
LÜTTGE U.,
STIMMEL K.H.,
SMITH J. A. C.,
GRIFFITHS H.
Publication year - 1986
Publication title -
plant, cell and environment
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 2.646
H-Index - 200
eISSN - 1365-3040
pISSN - 0140-7791
DOI - 10.1111/j.1365-3040.1986.tb01751.x
Subject(s) - crassulacean acid metabolism , malic acid , relative humidity , stomatal conductance , ecophysiology , humidity , vapour pressure deficit , epiphyte , bromeliaceae , botany , horticulture , transpiration , photosynthesis , chemistry , biology , meteorology , physics , citric acid , organic chemistry
The results described represent the first detailed measurements of gas exchange of epiphytic plants with crassulacean acid metabolism (CAM) in the humid tropics. A portable steady‐state CO 2 and H 2 O porometer was used to measure net exchange rates of CO 2 and H 2 O vapour ( J CO2 , J H2O ), leaf temperature ( T 1 ), air temperature ( T A ), air relative humidity (RH) and photosynthetically active radiation (PAR) for bromeliads in the field during the dry season in February and March 1983 on the tropical island of Trinidad. Different lengths of tubing (up to 25 m) were used so that the gas exchange could be measured of bromeliads in situ in their epiphytic habitats. Derived parameters such as leaf‐air water‐vapour‐concentration difference (Δ w ), water‐vapour conductance of leaves ( g ) and internal CO 2 partial pressure ( p i CO2 ) could be calculated. The particular problems of making such measurements in the humid tropics due to high relative humidities and high dew‐point temperatures are discussed. The long and often broad, strap‐like leaves of bromeliads are well suited for measurements with the steady‐state porometer. It is shown that CAM activity varies along the length of individual leaves, and variability between different leaves is also demonstrated. The major phases of CAM, i.e. nocturnal stomalal opening, CO 2 uptake and dark fixation as malic acid (Phase I), daytime stomatal closure and light‐dependent assimilation of CO 2 derived from decarboxylation of the malic acid (Phase III), and late‐afternoon stomatal opening with direct light‐dependent assimilation of atmospheric CO 2 (Phase IV) were all clearly shown by CAM bromeliads in situ. Their expression and magnitude depended on the environmental conditions. An early‐morning peak of CO 2 uptake as is characteristic of Phase II of CAM was not detected during the night‐day transition. A bromeliad intermediate between C 3 and CAM, Guzmania monostachia , showed substantial net CO 2 uptake in the early morning but no net uptake integrated over the whole of the night.