Seasonal and daily time course of the 13C composition in soil CO2 efflux recorded with a tunable diode laser spectrophotometer (TDLS)

Abstract

Temporal variations of carbon isotope composition of soil CO 2 efflux (F S and δ 13 C FS ) at different time scales should reflect both temporal variations of the climate conditions that affect canopy functioning and temporal changes in the relative contribution of autotrophic respiration to total F S . A tunable diode laser spectrophotometer (TDLS) was installed in the Hesse forest (northeast of France) early during the 2007 growing season to determine the seasonal and daily variability in δ 13 C FS . This method, based on the measurement of the absorption of an infrared laser emission at specific wave lengths of the 13 CO 2 and 12 CO 2 , allows the continuous monitoring of the two isotopologues. The concentrations of the two isotopologues in F S were continuously monitored from June to November 2007 using chamber method and Keeling plots drawn from nocturnal accumulation of CO 2 below the canopy. These TDLS measurements and isotope ratio mass spectrometer based Keeling plots gave very similar values of δ 13 C FS , showing the reliability of the TDLS system in this context. Results were analysed with regard to seasonal and daily changes in climatic and edaphic variables and compared with the δ 13 C of CO 2 respired by roots, litter and soil incubated under controlled conditions. Pronounced daily as well as seasonal variations in δ 13 C FS were recorded (up to 1.5‰). The range of variation of δ 13 C FS was of the same order of magnitude at both diurnal and seasonal scales. δ 13 C FS observed in the field fluctuated between values of litter and of root respiration recorded during incubation, suggesting that temporal (and probably spatial) variations were associated with changes in the relative contribution of the two compartments during the day and during the season.

Abiotic and seasonal control of soil-produced CO2 efflux in karstic ecosystems located in Oceanic and Mediterranean climates

“…The results reported here are consistent with many previous studies, in which a heavier isotopic source value is observed during drier and warmer seasons compared to the colder and wetter months of the year (Ekberg et al, 2007;Marron et al, 2009;Goffin et al, 2014). Other studies have related the variations in the δ 13 C of ecosystem and soil respiration to air humidity (Ekblad and Högberg, 2001;Bowling et al, 2002;Ekblad et al, 2005).…”

Environmental forcing does not induce diel or synoptic variation in the carbon isotope content of forest soil respiration

“…3, 5 and S1). Several studies have reported diel variation in the δ 13 C of the soil efflux (Bahn et al, 2009;Kodama et al, 2008;Marron et al, 2009), but in our case there was no diel variation in the δ 13 C of soil respiration (neither δ R , Fig. 5 nor δ J , Fig.…”

Challenges in measuring the δ13C of the soil surface CO2 efflux

“…Trying to accurately measure a 3% difference between two air streams (the chamber inflow and outflow) can be challenging, especially in the field. Using this type of open chamber to measure the d 13 CR S at natural abundance levels is clearly possible, as demonstrated recently, [11,68] but at low surface efflux rates there is a diminishing difference between the in-flowing and out-flowing chamber air (Fig. 3).…”

“…Because the TDLS and CRDS systems are less bulky and have lower power requirements than the IRMS instruments, they are more portable than the IRMS systems and they can be used in the field ( measurements. [11,13,56] The precision of the isotope measurements achievable with these systems is generally lower than that of IRMS (although the gap is closing), sample introduction systems for gases tend to be bespoke designs, and instrument control software is still an active area of development. However, the ability of these instruments to provide real-time isotope analysis in the field has opened up new and exciting possibilities across a variety of disciplines; this includes the characterisation of d 13 CR S .…”

“…This type of work, which has been undertaken in both forest and grassland systems, has utilised both natural abundance [9][10][11][12] and 13 C tracers. [13,14] Similarly, d…”