Feasibility of alternating heat pulses method for estimating sap flow and water content in plants

Abstract

Climate change combined with an increase in land use change have had major impacts on hydrological cycles and conservation of water resources. This represents a major challenge for water security at different scales, because when the impacts are noticed, the problem is already in a very advanced state. That is why it is very important to focus on understanding how these processes occur in order to anticipate possible vegetation response to these changes and take necessary preventive measures. In this context, monitoring the vegetation's water function is a key point for understanding the importance of vegetation in the hydrological cycle. Sap flow sensors are part of the basic technology for monitoring water use and real-time vegetation water status. In their simplest format, sap flow sensors are constituted of probes that apply heat to the plant stem. Heat dissipation is proportional to the water flow through the stem, allowing you to monitor transpiration and water use strategies in plants. However, the models of sap flow sensors available in the scientific literature present a series of problems such as high production cost, high energy consumption and have problems distinguishing changes in the flow of sap from changes in the water content of the tree, which difficulties its use on a large scale. In this project, PLANTEM (Technologies in Plants and Environmental Monitoring Ltda) proposes a new method of measuring sap flow: the alternating heat pulse method, based on a new working principle (alternating thermal properties of wood) and structural design. We hope that this new method (1) allows for complete production's automation, greatly reducing its cost; (2) has an energy consumption 100-1000 times lower than current sensors; and (3) allows to clearly distinguish the sap flow from the water content of the plant. To analyze the viability of the SF Plantem sensor, with its new architecture and using the alternating heat pulse method, we will I) model the sap flow sensor, physically validating its principle of operation, II) develop and manufacture prototypes of the sensor sap flow and III) test its functioning in relation to commercial sap flow sensors and alternative methods of measuring water flow and plant water content. In the first phase, we will hire a consultancy in thermodynamic modeling of fluids, and we hope to generate a model with physiological parameters of the tree and the sensor properties, which will be used for sensor self-calibration. The second phase will be the stage of prototypes` development and consecutive tests in the laboratory to improve the prototype. In phase 3 we will test and validate the sap flow sensor prototypes, carrying out three complementary experiments. In the first, we will evaluate the functioning of the sensor, measuring the flow in the laboratory by means of gravimetric validation. In the second, we will compare the measurements of the SF PLANTEM sensor with data collected with a gravimetric lysimeter, in an experiment with potted plants. Finally, we intend to compare data from the SF PLANTEM sensor, with data from the commercial sap flow sensor from the Australian company ICT and with a sensor from the heat dissipation method. In addition, we will measure some wood parameters of the sampled trees to assist in the validation of the method. The integration of all data will be analyzed by the entire body of researchers involved in this proposal and we hope in the end to arrive at a viable product for commercialization, simple to use, and energy saving. (AU)