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Title: An optical method for carbon dioxide isotopes and mole fractions in small gas samples: tracing microbial respiration from soil, litter, and lignin.

Source: Communications in Mass Spectrometry.

Author(s)Hall, Steven J.; Huang, Wenjuan; Hammel, Kenneth

Publication Year: 2017  View PDF »

Category: Journal Articles
Associated Research Project(s):   FPL-4712-2B

Abstract: RATIONALE: Carbon dioxide isotope (?13C value) measurements enable quantification of the sources of soil microbial respiration, thus informing ecosystem C dynamics. Tunable diode lasers (TDLs) can precisely measure CO2 isotopes at low cost and high throughput, but are seldom used for small samples (?5 mL). We developed a TDL method for CO2 mole fraction ([CO2]) and ??13C analysis of soil microcosms.

METHODS: Peaks in infrared absorbance following constant volume sample injection to a carrier were used to independently measure [12CO2] and [13CO2] for subsequent calculation of ?13C values. Using parallel soil incubations receiving differing C substrates, we partitioned respiration from three sources using mixing models: native soil organic matter (SOM), added litter, and synthetic lignin containing a 13C label at C? of the propyl side chain.

RESULTS: Once-daily TDL calibration enabled accurate quantification of ?13C values and [CO2] compared with isotope ratio mass spectrometry (IRMS), with long-term external precision of 0.17 and 0.31 for 5 and 1 mL samples, respectively, and linear response between 400 and 5000 ?mol mol-1 CO2. Production of CO2 from native soil C, added litter, and lignin C? varied over four orders of magnitude. Multiple-pool first-order decay models fitted to data (R2 > 0.98) indicated substantially slower turnover for lignin C? (17 y) than for the dominant pool of litter (1.3 y) and primed soil C (3.9 y).

CONCLUSIONS: Our TDL method provides a flexible, precise, and high-throughput (60 samples h-1) alternative to IRMS for small samples. This enables the use of C isotopes in increasingly sophisticated experiments to test biogeochemical controversies, such as the fate of lignins in soil.

Keywords: Carbon isotope; decomposition; kinetic fractionation; lignin; recalcitrance; soil respiration

Publication Review Process: Formally Refereed

File size: 1,024 kb(s)

Date posted: 10/05/2017

This publication is also viewable on Treesearch:  view
RITS Product ID: 88271
Current FPL Scientist associated with this product
Hammel, Kenneth E.
Research Chemist

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