Using 13C to Quantify Phloem Transport on Tall Plants in the Field.

Phloem transport dynamics play a crucial role in understanding the movement of photoassimilates within plants, particularly in tall species, where tracing carbon allocation and monitoring transport velocities present unique challenges. The difference in time lags between a labeling pulse of 13CO2 of the foliage and the appearance of labeled C in the respiration at different locations along the stem of a tall plant is used to estimate at which velocities the isotope tracer, i.e., the labeled carbohydrates, are transported in the phloem sap. Here, we describe a method for pulse labeling tall plants in the field and subsequently tracing 13C in the respiratory efflux of CO2.