Theoretical Proof and Empirical Confirmation of a Continuous Labeling Method Using Naturally 13C‐Depleted Carbon Dioxide

Continuous isotope labeling and tracing is often needed to study the transformation, movement, and allocation of carbon in plant‐soil systems. However, existing labeling methods have numerous limitations. The present study introduces a new continuous labeling method using naturally 13C‐depleted CO2. We theoretically proved that a stable level of 13C‐CO2 abundance in a labeling chamber can be maintained by controlling the rate of CO2‐free air injection and the rate of ambient airflow with coupling of automatic control of CO2 concentration using a CO2 analyzer. The theoretical results were tested and confirmed in a 54 day experiment in a plant growth chamber. This new continuous labeling method avoids the use of radioactive 14C or expensive 13C‐enriched CO2 required by existing methods and therefore eliminates issues of radiation safety or unaffordable isotope cost, as well as creating new opportunities for short‐ or long‐term labeling experiments under a controlled environment.