Measuring root flow rate as a surrogate for root pressure

The phenomenon of root pressure has long intrigued plant biologists, but many aspects of its function and mechanism remain in question. Different methods are used to assess it. Here we compare two common methods, direct measurement with pressure transducers and measurements of root (sap) flow, which are assumed to proxy root pressure. We found different relationships between these measurements among genotypes of maize and sorghum, indicating that a more intricate understanding of root pressure and mechanisms involved is needed. We suggest that measurements of root flow may be governed by membrane permeability and, potentially, xylem anatomy, in addition to root pressure. Ultimately, a better understanding of these processes and mechanisms will advance not only our fundamental understanding, but our ability to use these traits to improve plant fitness in diverse systems through breeding.