Sensors and instrumentation to measure Sap flow in small stem plants

Heat-based sap flow sensors are widely used in research to analyse plant-water relationships and to study water flow dynamics of plants to determine the water requirements for optimum growth. To date, the majority of field studies of sap flow have been conducted in large plants, with only a few methods being suitable for small stems of less than 10 mm in diameter. This paper discusses the suitability of sensors and electronic designs for a heat-based method to monitor sap flows over the velocity range 2-150 cm/hr, in a small plant stems of 5 to 10 mm in diameter. Three heat-pulse methods (Compensated Heat Pulse, Heat Ratio and Tmax) were tested using both internal and external sensor designs. Based on preliminary findings, two alternative methods of analysis were developed and tested in the laboratory. A short field experiment was carried out to compare heat pulse velocity and global solar radiation. We found the external sensor was not suitable for small stems (<; 20 mm diam.) with thick (> 3mm) bark. A small internal sensor showed more promising results for resolving a wider range of sap flows and tracking the influence of global solar radiation.

[1]  G. Goldstein,et al.  Heat dissipation sensors of variable length for the measurement of sap flow in trees with deep sapwood. , 2002, Tree physiology.

[2]  B. Olbrich.  The verification of the heat pulse velocity technique for estimating sap flow in Eucalyptusgrandis , 1991 .

[3]  Gaylon S. Campbell,et al.  Improved heat balance method for determining sap flow rate , 1991 .

[4]  J. Ham,et al.  Heat balance sap flow gauge for small diameter stems , 1993 .

[5]  R. H. Swanson,et al.  A Numerical Analysis of Heat Pulse Velocity Theory and Practice , 1981 .

[6]  Brent Clothier,et al.  Theory and Practical Application of Heat Pulse to Measure Sap Flow , 2003 .

[7]  T. Dawson,et al.  DETERMINING THE WATER DYNAMICS OF FLOWERING USING MINIATURE SAP FLOW SENSORS , 2012 .

[8]  Subhas Chandra Mukhopadhyay,et al.  Intelligent Sensing, Instrumentation and Measurements , 2013 .

[9]  R. Swanson.  Significant historical developments in thermal methods for measuring sap flow in trees , 1994 .

[10]  Improving heat-pulse methods to extend the measurement range including reverse flows , 2012 .

[11]  C. Leuschner,et al.  In situ water absorption by tree fine roots measured in real time using miniature sap‐flow gauges , 2002 .

[12]  M. Adams,et al.  An improved heat pulse method to measure low and reverse rates of sap flow in woody plants. , 2001, Tree physiology.

[13]  D. Marshall.  Measurement of Sap Flow in Conifers by Heat Transport. , 1958, Plant physiology.

[14]  S. Allen,et al.  Measurement of sap flow in plant stems , 1996 .

[15]  M. Fuchs,et al.  Improvement of the heat pulse method for determining sap flow in trees , 1981 .

[16]  B. Dichio,et al.  An external heat pulse method for measurement of sap flow through fruit pedicels, leaf petioles and other small-diameter stems. , 2009, Plant, cell & environment.