High-Throughput and Homogeneous 13C-Labelling of Plant Material for Fair Carbon Accounting in Maize Cropping Systems
Johanna I.F. Slaets, Christian Resch, Leopold Mayr, Georg Weltin, Maria Heiling, Roman Gruber, Gerd Dercon
United Nations, Joint FAO/IAEA Division of Nuclear Techniques in Food and Agriculture, Austria
With growing political acknowledgement of the anthropogenic drivers and consequences of climate change, development of carbon accounting mechanisms is essential to distribute the burdens of greenhouse gas emission mitigation. Therefore, carbon storage and emission must be accurately quantified. Plant material labelled with 13C can be used to measure carbon storage and carbon dioxide emission of various cropping practices under local conditions, both via in situ and incubation experiments. Such an approach, however, is only useful to stakeholders when plant material can be labelled homogeneously, cost-effectively and in sufficient quantity. Current pulse labelling methods often result in heterogeneous signatures and produce only limited amounts of material. We developed a high-throughput method in a walk-in growth chamber of 12 m3, where ambient CO2 concentration and isotopic composition are continuously monitored by an off-axis integrated cavity output spectroscope (Los Gatos Research), and are held at a δ13C value between 350 and 400‰. Maize was chosen as a first test crop because of its global importance as cash crop and animal fodder, as well as the possibility to produce considerable amounts of biomass, yielding one kilogram dry matter of plant material per run. The resulting material showed a homogeneous isotopic labelling and variability in isotopic signature decreased with leaf age. Bottom leaves had an average δ13C value of 277‰, with a 95% confidence interval of [247, 307] whereas top leaves showed an average δ13C value of 366‰, the 95% confidence interval equalling [362, 370]. As C uptake by the plants in the initial growing phase is low, the effects of chamber leaking, although limited, were larger during this stage, which could be compensated for by having higher 13C concentrations during early growth stages. Future steps of high-throughput 13C labelling will focus on legumes and other cereal crops, opening research avenues for better understanding carbon dynamics in existing crop rotation systems. Furthermore, dual labelling with 13C and 15N would enable simultaneous accounting of not only CO2 but also CO2-equivalent emissions, such as N2O. High-throughput isotopic labelling of plant material can thus provide accurate and cost-effective methods to establish fair plans for greenhouse gas emission reduction.
Keywords: 13C, carbon accounting, CO2, greenhouse gas emissions, stable isotopes
Contact Address: Johanna I.F. Slaets, United Nations, Joint FAO/IAEA Division of Nuclear Techniques in Food and Agriculture, Technikerstr. 8/7, 2340 Moedling, Austria, e-mail: hanna.slaetsgmail.com