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

Abstract

There are scientific benefits for using an automated closed steady-state flow ¹³C (carbon; C) plant–soil labeling system (PSLS) for online recording and adjustment of ¹³CO₂ (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 ¹³CO₂ for 2 and 6 h continuously. Analyses of the ¹³C/¹²C isotope using isotope ratio mass spectrometry of plant, soil solution, and rhizosphere soil samples showed that the injected ¹³CO₂ was closely correlated with the ¹³C pools. The labeled ¹³C root exudates at tillering stage to rhizosphere soil increased from 0.4 ± 0.1 mg ¹³C pot⁻¹ (four plants) after 2 h to 2.5 ± 1.0 mg ¹³C pot⁻¹ after 6 h of labeling. The steady-state PSLS permits rapid control and maintenance of ¹³C by ¹³CO₂ injection, enabling detailed examination of the C budget over short labeling periods.

• ¹³C/¹²C isotope mass ratio
• ¹³CO₂ labeling
• LI-COR 7000
• root exudates

Acknowledgments

We are indebted to Alain Saumure and Mathew Kenny from AAFC for constructing the chambers and to Devon Worth and Dave Dow from AAFC for their advice. We acknowledge Ron Wheeler, George Hill, and Art Smith for sampling the soils and their assistance in setting up the greenhouse studies. We appreciate also the efforts of many summer students for helping us to complete this work on time. We also thank Pamela Thurlow and Roland Kroebel for their critical readings of the manuscript. We acknowledge the anonymous reviewers and editor for their comments on the manuscript.