Sap Flow Case Studies from Japan
Translated from ICT International Japanese Newsletter
The ICT International Sap Flow Meter (SFM1) is used by researchers all around the world. The SFM1 utilises the Heat Ratio Method (HRM), a thermometric method developed by Australian scientists in the 1990’s. The HRM is a major advance on previous techniques in that it can measure low and reverse sap flow, as well as high rates of flow. The SFM1 has been widely adopted by researchers in Australia, United States, Germany, Spain, Italy, Brazil, Colombia, Costa Rica and India. Recently, there has been a surge of interest from Japanese researchers and two case studies from Japan are outlined.
Case Study 1: Avocado in Greenhouse
Dr. Asada, Tamagawa University, measured sap flow with the SFM1 in an avocado tree in the greenhouse on the campus of Tamagawa University. The SFM1 was installed in the trunk which had a 7cm diameter. The tree had no fruit.
Figure 1 shows an example data set of raw heat velocity over a 12 day period. After installation on the first day, the subsequent three days were characterised by cool and cloudy weather. The next three days were warm and sunny followed by a day of rainfall. The last four days were also warm and sunny.
Figure 1. Raw heat velocity from an SFM1 installed on an avocado. The green line is the outer measurement point and blue line is inner measurement point from the same sapwood radial profile.
There are two lines presented on Figure 1 representing two measurement points within the sapwood. These measurement points are known as outer and inner and are situated at 0.75cm and 2.25cm depth into sapwood. By having two measurement points the SFM1 provides data on the radial profile of sap flow in plants. For this avocado tree the inner measurement point has slightly less rates of sap flow than the outer measurement point.
Although Figure 1 only shows raw heat velocity it demonstrates sap flow can be measured in avocado using the SFM1. Further collection of data, including correction factors such as sapwood fresh and dry weight, thermal diffusivity, and wound response, will provide actual rates of sap flow (expressed as litres of water transpired per hour or day). Correlating sap flow data with weather variables, such as solar radiation and vapour pressure deficit (VPD), as well as across experimental treatments, can provide an even more meaningful interpretation of sap flow in avocado.
Dr.Asada is very interested in applying this technology to other fruit trees especially as he now recognises the ability of the SFM1 to measure low flow and reverse flow.
Figure 2. SFM1 installed on an avocado tree growing in a glasshouse at Tamagawa University.
Case Study 2: Japanese Cedar (Cryptomeria spp.)
Dr.Hashimoto, Shimane University, measured sap flow in Japanese Cedar with a SFM1 instrument. Measurements were carried out at the Shimane University planted forest, Matsue campus in Matsue, Shimane Prefecture.
The SFM1 probes were installed at breast height on a tree with a diameter of 18cm. At the time of installation a stem core was taken from the tree and correction factors such as bark depth, sapwood depth, sapwood fresh and dry weight were measured. This data was then inserted into Sap Flow Tool software (www.sapflowtool.com) to convert raw heat velocity data into sap flow data.
Figure 3. SFM1 installed on a Japanese Cedar, Shimane University. Notice removal of bark so sap flow probes are installed on sapwood.
Figure 4 shows 18 days of sap flow data from the measured tree. Similar to the avocado case study above, an outer and inner measurement point were measured by the SFM1. In this case, the inner measurement point exhibits markedly less sap flow than the outer measurement point. Interestingly, the radial profile in this tree shows different nocturnal rates of flow: the inner measurement point shows zero flow whereas the outer measurement point shows positive flow at night. The SFM1 has been used by other researchers to examine patterns of nocturnal flow (e.g. Pfautsch et al. 2011; Zeppel et al. 2011) because of its ability to measure rates of low and reverse flow (which commonly occur at night).
Figure 4. Sap flow and sap volume data for a Japanese Cedar during spring, 2011. The green line is the outer measurement point and blue line is inner measurement point from the same sapwood radial profile. The gray line is sap volume (right hand axis).
Another interesting pattern occurs around day 13 in which there is zero and even reverse rates of sap flow. On this day there was a rain event at the field site. It will be interesting to correlate the sap flow data with weather variables such as solar radiation and VPD.
The right hand axis on Figure 4 indicates daily sap volume (cm3). These data can be divided by 1000 to give sap volume in litres of water per day. This Japanese Cedar, at this field site during this time of year (early May), was transpiring approximately 40 litres of water per day.
Burgess, S. S. O., M. A. Adams, et al. (2001). “An improved heat pulse method to measure low and reverse rates of sap flow in woody plants.”
Tree Physiology 21: 589-598.
Pfautsch, S., C. Keitel, et al. (2011). “Diurnal patterns of water use in Eucalyptus victrix indicate pronounced desiccation–rehydration cycles despite unlimited water supply.”
Tree Physiology 31: 1041-1051.
Zeppel, M. J. B., J. D. Lewis, et al. (2011). “Interactive effects of elevated CO2 and drought on nocturnal water fluxes in Eucalyptus saligna.”
Tree Physiology 31(9): 932-934.