Producing Isotopically Enriched Plant, Soil Solution, and Rhizosphere Soil Materials over a Few Hours

There are scientific benefits for using an automated closed steady-state flow C-13 (carbon; C) plant-soil labeling system (PSLS) for online recording and adjustment of (CO2)-C-13 (carbon dioxide) concentration equivalents to those used by photosynthesis, as compared to widely used uncontrolled open pulse labeling systems. Wheat plants were labeled at four growth stages (four leaves, tillering, late boot, and early dough) with (CO2)-C-13 for 2 and 6 h continuously. Analyses of the C-13/C-12 isotope using isotope ratio mass spectrometry of plant, soil solution, and rhizosphere soil samples showed that the injected (CO2)-C-13 was closely correlated with the C-13 pools. The labeled C-13 root exudates at tillering stage to rhizosphere soil increased from 0.4 +/- 0.1 mg C-13 pot(-1) (four plants) after 2 h to 2.5 +/- 1.0 mg C-13 pot(-1) after 6 h of labeling. The steady-state PSLS permits rapid control and maintenance of C-13 by (CO2)-C-13 injection, enabling detailed examination of the C budget over short labeling periods.