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A new measurement technique reveals temporal variation in δ 18 O of leaf‐respired CO 2
Author(s) -
BARBOUR MARGARET M.,
FARQUHAR GRAHAM D.,
HANSON DAVID T.,
BICKFORD CHRISTOPHER P.,
POWERS HEATH,
MCDOWELL NATE G.
Publication year - 2007
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.1365-3040.2007.01633.x
Subject(s) - analytical chemistry (journal) , oxygen 18 , flux (metallurgy) , isotope , stable isotope ratio , delta , mass spectrometry , absorption (acoustics) , chemistry , spectrometer , resolution (logic) , steady state (chemistry) , isotopes of oxygen , environmental chemistry , physics , chromatography , nuclear chemistry , optics , organic chemistry , quantum mechanics , astronomy , artificial intelligence , computer science
The oxygen isotope composition of CO 2 respired by Ricinus communis leaves ( δ 18 O R ) was measured under non‐steady‐state conditions with a temporal resolution of 3 min using a tunable diode laser ( TDL ) absorption spectrometer coupled to a portable gas exchange system. The SD of δ 18 O measurement by the TDL was ± 0.2‰ and close to that of traditional mass spectrometers. Further, δ 18 O R values at isotopic steady state were comparable to those obtained using traditional flask sampling and mass spectrometric techniques for R. communis grown and measured in similar environmental conditions. As well as higher temporal resolution, the online TDL method described here has a number of advantages over mass spectrometric techniques. At isotopic steady state among plants grown at high light, the ‘one‐way flux’ model was required to accurately predict δ 18 O R . A comparison of measurements and the model suggests that plants grown under low‐light conditions have either a lower proportion of chloroplast CO 2 that isotopically equilibrates with chloroplast water, or more enriched δ 18 O of CO 2 in the chloroplast that has not equilibrated with local water. The high temporal resolution of isotopic measurements allowed the first measurements of δ 18 O R when stomatal conductance was rapidly changing. Under non‐steady‐state conditions, δ 18 O R varied between 50 and 220‰ for leaves of plants grown under different light and water environments, and varied by as much as 100‰ within 10 min for a single leaf. Stomatal conductance ranged from 0.001 to 1.586 mol m −2 s −1 , and had an important influence on δ 18 O R under non‐steady‐state conditions not only via effects on leaf water H 2 18 O enrichment, but also via effects on the rate of the one‐way fluxes of CO 2 into and out of the leaf.