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A new measurement technique reveals rapid post‐illumination changes in the carbon isotope composition of leaf‐respired CO 2
Author(s) -
BARBOUR MARGARET M.,
MCDOWELL NATE G.,
TCHERKEZ GUILLAUME,
BICKFORD CHRISTOPHER P.,
HANSON DAVID T.
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.1365-3040.2007.01634.x
Subject(s) - fractionation , phloem , respiratory quotient , darkness , isotopes of carbon , chemistry , photosynthesis , respiration , botany , composition (language) , flux (metallurgy) , carbon fibers , substrate (aquarium) , horticulture , biology , chromatography , environmental chemistry , biochemistry , materials science , total organic carbon , ecology , linguistics , philosophy , organic chemistry , composite number , composite material
We describ an open leaf gas exchange system coupled to a tunable diode laser (TDL) spectroscopy system enabling measurement of the leaf respiratory CO 2 flux and its associated carbon isotope composition ( δ 13 C Rl ) every 3 min. The precision of δ 13 C Rl measurement is comparable to that of traditional mass spectrometry techniques. δ 13 C Rl from castor bean ( Ricinus communis L.) leaves tended to be positively related to the ratio of CO 2 produced to O 2 consumed [respiratory quotient ( RQ )] after 24–48 h of prolonged darkness, in support of existing models. Further, the apparent fractionation between respiratory substrates and respired CO 2 within 1–8 h after the start of the dark period was similar to previous observations. In subsequent experiments, R. communis plants were grown under variable water availability to provide a range in δ 13 C of recently fixed carbohydrate. In leaves exposed to high light levels prior to the start of the dark period, CO 2 respired by leaves was up to 11‰ more enriched than phloem sap sugars within the first 10–15 min after plants had been moved from the light into the dark. The 13 C enrichment in respired CO 2 then decreased rapidly to within 3–7‰ of phloem sap after 30–60 min in the dark. This strong enrichment was not observed if light levels were low prior to the start of the dark period. Measurements of RQ confirmed that carbohydrates were the likely respiratory substrate for plants ( RQ > 0.8) within the first 60 min after illumination. The strong 13 C enrichment that followed a high light‐to‐dark transition coincided with high respiration rates, suggesting that so‐called light‐enhanced dark respiration (LEDR) is fed by 13 C‐enriched metabolites.