New, open-source miniature external sap flow gauges for capturing plant water use

Miniature external sap flow gauges are a useful tool for investigating water use of leaves and small shoots, yet have been utilized sparingly in academic research, agriculture, and related fields. Low adoption of sap flow technology could be related to the prohibitively high cost of commercially available products and/or significant time requirements to independently manufacture the instruments. Here, we present an inexpensive, easy-to-manufacture external sap flow gauge with integrated Arduino-based logger that we believe has the potential to be widely and rapidly applied. We provide the results of an investigation into the performance of the gauges as well as information about our open-source platform that provides instructions on how to manufacture, assemble and use the gauges. To test the ability of the gauges to capture plant water use, we installed 12 instruments on plants growing in both a glasshouse and in a field environment. We then simultaneously monitored sap flow and leaf-level gas exchange (using a LI-COR LI-6800) over a diurnal period. Our results show that the gauges can effectively capture variable plant water use in both settings. Our plug-and-play gauges are cost effective, open-source, and can be manufactured rapidly. In addition, the stand-alone gauges and micro-loggers can be easily installed on any tree or shrub and will transmit data wirelessly to hand-held devices (e.g. cell phones or laptops). These remarkable advancements in sap flow technology provide a promising future for the use of sap flow and have the potential to advance our understanding of plant biology.