Real-time Measurements of Carbon Partitioning in Plants Using $^{11}$CO$_2$

Understanding the effects that increased levels of atmospheric carbon dioxide (CO$_2$) can have on plants is of global importance. Of particular concern is the effect on crop yield and plant growth, as well as the potential of long-term carbon sequestration via natural processes. To better understand plant response to increased CO$_2$ levels, we use a short half-life radioisotope labelling process to trace the dynamics of carbon allocation and translocation within the plant. Using the positron-emitter carbon-11, which is produced at Triangle Universities Nuclear Laboratory via the reaction $^{14}$N(p, $\alpha$)$^{11}$C, we are able to introduce $^{11}$CO$_2$ to plants grown at current and projected CO$_2$ concentrations at the Duke University Phytotron. Positron emission imaging techniques are then used to trace the transport and distribution of carbon throughout the plant. Results from collimated, single-detector measurements and a low spatial resolution ($\sim$1cm) planar positron emission imager will be presented, as well as plans for $^{13}$N studies and the construction of a high spatial resolution ($\sim$3mm) planar imager.