Opportunities and challenges in the use of radiotracers to measure phloem transport are discussed, with an emphasis on noninvasive techniques to trace photoassimilate, carbon's short-lived isotope 11C, and an eye to pitfalls and traps to avoid. We discuss in turn the rationale for using tracers, the limitations and complications with using short-lived radiotracers like 11C, the physics of decay and detection that need to be known when data are interpreted, and methods of analysis.
Keywords: 11C; 14C; 18F; Carbon allocation; Carbon-11; Carbon-14; Radiocarbon; Radiotracers.