Carbon assimilation and turnover in grassland vegetation using anin situ13CO2 pulse labelling system

Abstract

A mobile laboratory was developed to administer a controlled flow of 13C labelled CO2 at ambient concentrations (∼350 ppm) in the field. The stable isotope delivery (SID) system consists of an isotope‐mixing unit with flow control to a series of 12 independent labelling chambers. In‐line CPU controlled infrared gas analysers allow automated measurement of chamber CO2 concentrations and gas flow management. A preliminary experiment was established on an upland pasture located at the NERC Soil Biodiversity experimental site, Sourhope, UK, in August 1999. The objective of this investigation was to determine the magnitude of pulse‐derived C incorporation into a typical upland plant community. To achieve this, the SID system was deployed to pulse‐label vegetation with CO2 enriched with 13C (50 atom %) at ambient concentrations (∼350 ppm) on two consecutive days in August 1999. Samples of headspace CO2, shoot and root were taken on four occasions over a period of 28 days after 13C labelling. These materials were then prepared for 13C/12C ratio determination by continuous‐flow/combustion/isotope ratio mass spectrometry (CF‐C‐IRMS). Results showed that pulse derived CO2‐C was assimilated at a rate of 128 ± 32 µg g shoot‐C hour−1. Dynamic samplings showed that pulse‐derived 13C concentrations in the labelled plant tissues declined by 77.4 ± 6% after 48 hours. The rapid decline in 13C concentrations in plant matter was the result of C loss from the plant in the form of respired CO2 and root exudates, and dilution by subsequent unlabelled C assimilates. This novel system offers considerable potential for in situ tracer investigations. Copyright © 2000 John Wiley & Sons, Ltd.

Field <sup>13</sup>CO<sub>2</sub> pulse labeling reveals differential partitioning patterns of photoassimilated carbon in response to livestock exclosure in a <i>Kobresia</i> meadow

“…A lower proportion of recovered 13 C (10 %) is lost from shoots by shoot respiration and belowground transport in the fenced plots than that in the grazed plots (16 %) during the first 24 h after labeling. These estimations in the two treatments were much lower than the value of 36.7 % reported by Wu et al (2010) and 77 % found by Ostel et al (2000).…”

Physiological and Community Responses of EstablishedGrassland Bacterial Populations to WaterStress

“…It may therefore be likely that changes occurring in these operationally defined active communities may be more relevant in terms of ecosystem functioning. Further, technologies which directly link the activity of microbes with ecosystem processes, such as the labeling of plant material with 13 CO 2 (37) and phylogenetic analysis of isotopically enriched rRNA (30), may be a more appropriate way of subdividing the community for more-resolved analyses of the response to perturbation.…”

Soil organic matter dynamics: a biological perspective derived from the use of compound‐specific isotopes studies

“…DNA and RNA enable description of the total and active community, respectively (Ostle et al 2000;Kreuzer-Martin 2007). The involvement in the decomposition process can only be traced with highly labeled substrates using stable isotope probing (Kreuzer-Martin 2007).…”