BOREAS TE-12 SSA Water Potential Data Summary The BOREAS TE-12 team collected water potential data in 1993 and 1994 from aspen, jack pine and black spruce leaves/needles. Collections were made at the SSA FEN, YJP, YA, OA, and OBS sites. Measurements were made using a pressure chamber on a platform in the field. The data are provided in tabular ASCII files. Table of Contents * 1 Data Set Overview * 2 Investigator(s) * 3 Theory of Measurements * 4 Equipment * 5 Data Acquisition Methods * 6 Observations * 7 Data Description * 8 Data Organization * 9 Data Manipulations * 10 Errors * 11 Notes * 12 Application of the Data Set * 13 Future Modifications and Plans * 14 Software * 15 Data Access * 16 Output Products and Availability * 17 References * 18 Glossary of Terms * 19 List of Acronyms * 20 Document Information Data Set Overview 1.1 Data Set Identification BOREAS TE-12 SSA Water Potential Data 1.2 Data Set Introduction Measurements of shoot, branchlet, and leaf water potential were made in the field on samples cut for measurement of leaf optical properties and shoot geometry. 1.3 Objective/Purpose The purpose of this study was to characterize the water potential of boreal forest plant elements. 1.4 Summary of Parameters Water potential of shoots, branchlets, and leaves/needles of black spruce, jack pine or aspen samples. 1.5 Discussion Intensive Field Campaign (IFC)-93: Measurements were made on samples collected at two sites in the BOReal Ecosystem-Atmosphere Study (BOREAS) Southern Study Area (SSA): near the Nipawin Fen (FEN) and Nipawin Jack Pine (Young-Dry) (YJP). Canopy access was limited to only ground-level collection of samples. Samples from trees could be from various heights within the tree, but were generally from the lower third of the entire canopy height. Aspen [Populus tremuloides], black spruce [Picea mariana], and jack pine [Pinus banksiana] were sampled near the SSA-FEN site. Jack pine needles were sampled at the SSA-YJP site. IFC-1,2,3: Measurements were made on samples collected at four sites in the SSA: Young Aspen (YA), Old Aspen (OA), YJP, and Old Black Spruce (OBS). Aspen branchlets were sampled at SSA-YA and SSA-OA. Jack pine shoots were sampled at SSA-YJP. Black spruce shoots were sampled at SSA-OBS. 1.6 Related Data Sets BOREAS TE-12 SSA Shoot Geometry Data BOREAS TE-12 SSA Water Potential Data BOREAS TE-10 Shoot Biodirectional Reflectance BOREAS RSS-08 Reflectance Data 2.Investigator 2.1 Investigator(s) Name and Title Elizabeth A. Walter-Shea, Assoc. Professor 2.2 Title of Investigation Radiation and Gas Exchange of Canopy Elements in a Boreal Forest 2.3 Contact Information Contact 1 Mark A. Mesarch University of Nebraska - Lincoln Lincoln, NE (402) 472-5904, (402) 472-0284 (402) 472-6614 (fax) mmesarch@unlinfo.unl.edu Contact 2 Elizabeth A. Walter-Shea University of Nebraska - Lincoln Lincoln, NE (402) 472-1553 (402) 472-6614 (fax) agme012@unlvm.unl.edu Contact 3 Cynthia J. Hays University of Nebraska - Lincoln Lincoln, NE (402) 472-6701 (402) 472-6614 (fax) agme025@unlvm.unl.edu Contact 4 Shelaine Curd Raytheon STX Corporation NASA/GSFC Greenbelt, MD (301) 286-2447 (301) 286-0239 (fax) shelaine.curd@gsfc.nasa.gov 3.Theory of Measurements Water potential is a measure of the free energy of water in comparison to the free energy of pure water. The water potential of pure water has been assigned a value of 0 bars. A bar is a pressure unit directory relatable to energy per unit mass (1 bar = 0.1 MPa = 0.987 atmospheres). The chemical energy of water in the biosphere is lower than pure water and therefore values are expressed as negative numbers (Barbour et al., 1980). Water potential is often measured using a pressure chamber. Measuring the xylem pressure potentials is based on the fact that negative pressures (tensions) exist in the xylem and, when stems are severed, the pressure necessary to force water back to the cut surface is equivalent to the negative pressure in the xylem prior to cutting. An advantage of the pressure chamber lies in the large number of samples that can be measured in a short time. The apparatus has also been made portable so that data may be taken on plants in their native surroundings (Barbour et al., 1980). Water potential is an important moisture measurement of water transport in a plant and of plant growth. Water potential is one of the variables that can drive stomatal control, allowing the interchange of gases for the photosynthesis process. Water content of the plant also affects the absorption pattern of the plant in the infrared portion of the energy spectrum. Branchlets or leaves selected for water potential measurements were not the same samples used for optical property or shoot/leaf geometry measurements. (See BOREAS TE-12 Leaf Optical Data for SSA Species.) For conifer samples, branchlets were selected from the same branch used to collect samples for the other measurements. For deciduous samples, leaves selected for water potential measurements were selected from branches near those used for collection of samples for the other measurements. 4. Equipment 4.1 Instrument Description A pressure chamber designed by Precision Machine Co. was used to measure water potential of shoots and leaves in 1993. Nitrogen gas was used to pressurize the chamber. Precision of this chamber was 0.01 MPa. The Model 1002 Plant Moisture Stress Measurement Instrument was used in IFC-1, IFC-2, and IFC-3 in 1994. The pressure-measuring transducer was +/- 0.5 % full scale. Nitrogen gas was used to pressurize the chamber. Precision of this chamber is 0.007 MPa. 4.1.1 Collection Environment All measurements were made in the field. 4.1.2 Source/Platform None given. 4.1.3 Source/Platform Mission Objectives None given. 4.1.4 Key Variables Water potential of shoots, leaves, and leaflets. 4.1.5 Principles of Operation Nitrogen gas is released into the chamber at an initial rate of less than 0.1 MPa s-1 and slowed to less than 0.02 MPa s-1 until water begins to appear on the xylem openings of the stem or petiole. 4.1.6 Instrument Measurement Geometry The pressure chamber is set on a platform in the field. A magnifying glass and light source are hand-held to help view the xylem elements. 4.1.7 Manufacturer of Instrument PMS Instrument Company 270 NW Royal Oaks Dr. Corvallis, OR 97330 (503) 752-7926 (503) -752-7929 (fax) Precision Machine Company, Inc. 2933 North 36th Street Lincoln, NE 68504 (402) 467-5528 (402) 467-5530 (fax) 4.2 Calibration 4.2.1 Specifications No calibration of instruments. 4.2.1.1 Tolerance None. 4.2.2 Frequency of Calibration None. 4.2.3 Other Calibration Information None. 5.Data Acquisition Methods The CANOPY_LOCATION parameter of the data set is a relative measure based upon the height of the sample location relative to the height of the canopy. Therefore, a sample collected from the top of a short tree in a tall canopy and a sample collected from the bottom of a short tree in a short canopy can both be designated as "low" for the HEIGHT parameter. Samples were collected from HIGH and LOW portions of the canopy at SSA-OBS and SSA-YJP. Samples were collected from LOW portions of the canopy at SSA-FEN. 5.1 Sample Collection Sample Gathering: FOR IFC-93 and IFC-1,2,3: Branchlet samples (defined as a small tree limb consisting of shoots with growth from current year, previous year, and 2 years ago) were cut from plants, covered with damp cheesecloth, sealed in a ziplock-type storage bag, and stored in a cool ice chest. 5.2 Sample Measurement For the jack pine and black spruce trees, shoots with at least 3 years of needle growth were cut from the branchlet for water potential measurement. Aspen leaves from SSA-OA have petioles thick enough to maintain xylem integrity and view the xylem elements with the magnifying glass that was used in the field; therefore, individual leaves were used. Aspen leaves from SSA-YA and SSA-FEN were small and tender, so several leaves on a branchlet (usually three leaves) were used. Samples were draped with wet cheesecloth and placed in a plastic bag. The petiole, branchlet, or shoot end was placed through a rubber stopper so the cut end of the plant element was exposed approximately 5-10 mm through the stopper. The shoot end near the inside side stopper may have been wrapped with clay to assist in sealing the chamber. The stopper was placed in the chamber top and the chamber was sealed. Nitrogen gas was released into the chamber at an initial rate of less than 0.1 MPa s-1 and slowed to less than 0.02 MPa s-1 until water began to appear on the xylem openings of the stem. The pressure is recorded by hand and/or electronically. The pressure was released slightly, and then a second measurement was made. 6. Observations 6.1 Data Notes None. 6.2 Field Notes Measured: 04-Aug-1993 Coordinated water potential measurement with samples collected for shoot geometry from jack pine shoots collected near SSA-FEN; 3 trees x 1 branch x 3 replications of shoots. Branches from trees 1 and 2 were sunlit and the branch from tree 3 was shaded. Measured: 04-Aug-1993 Coordinated measurements of water potential, leaf area, and leaf optical properties from aspen near SSA-FEN; 3 trees x 3 branches x 3 replications. The first replication was for a leaf at the top of the branchlet in the second replication was for a leaf in the middle of the branchlet, and the third replication was for a leaf on the lowest part of the branchlet. Branches were selected from the north side of the trees. Measured: 06-Aug-1993 Coordinated measurements of shoot water potential, leaf gas exchange, leaf optical properties, and shoot geometry on black spruce near SSA-FEN; 3 trees x 4 branches x 3 replications. Tree 1 was sunlit, tree 2 was lightly shaded, and tree 3 was deeply shaded. All trees were about 3 to 3.5 m tall in a grove of trees about 10 m tall. Measured: 16-Aug-1993 Coordinated water potential measurement with samples collected for shoot geometry from jack pine shoots collected at SSA-YJP; 9 trees x 1 branch x 3 ages x 1 replication of shoot. Measured: 26-May-1994 Coordinated water potential, shoot geometry, and leaf optical properties on jack pine shoots collected at SSA-YJP; 9 trees x 1 branch x 3 replications. Trees located about 150 m east of the hut and 20-50 m north of the access road. Branches were from the south side of the trees and generally in full sunlight at 1230-1600 local time. Branches were collected from 2-3 m from the soil surface. Measured: 29-May-1996 Coordinated measurements of water potential, leaf area, and leaf optical property on aspen leaves collected at SSA-YA; 3 trees x 3 branches x 3 replications. Leaves were from branches sampled from the south side of the tree and 1.5-2 m from the soil surface. Measured: 01-Jun-1994 Coordinated measurements of water potential, leaf optical properties, and shoot geometry from black spruce shoots collected at SSA-OBS; 3 trees x 3 branches x 3 replications. Samples were collected from the top of the trees via the canopy access tower and on the south-facing side of the trees. Branches were sunlit. Measured: 04-Jun-1994 Coordinated measurements of water potential, leaf optical property, gas exchange measurements, and shoot geometry from jack pine shoots. Samples were collected at SSA-YJP; 4 trees x 1 branch x 3 replications. Measured: 07-Jun-1994 Coordinated measurements of water potential, leaf optical property, and shoot geometry from black spruce shoots collected at SSA-OBS; 3 trees x 3 branches x 3 replications. Samples were collected from lower in the canopy (approximately 9 m from the soil surface) via the canopy access tower. Branches from tree 1 and 2 were mostly shaded. Branches from tree 3 were sunlit most of the time. Measured: 07-Jun-1994 Coordinated measurements of water potential, leaf area, and leaf optical properties from aspen collected at SSA-YA; 3 trees x 3 branches x 3 replications from sunlit branches at the top of the canopy. Measured: 10-Jun-1994 Coordinated measurements of water potential, leaf optical properties, and shoot geometry from jack pine shoots collected at SSA-YJP; 9 trees x 1 branch x 3 replications. Trees located about 150 m east of the hut and 20-50 m south of the access road. Branches were from the south side of trees and sunlit. Branches were collected from the top of the canopy. Measured: 15-Jun-1994 Coordinated measurements of water potential, leaf area, and leaf optical properties from aspen collected at SSA-YA; 3 trees x 3 branches x 3 replications for the top of the canopy; measured adaxial and abaxial surfaces. Rain fell during measurements. Measured: 21-Jul-1994 Coordinated measurements of water potential, leaf optical properties, and shoot geometry from jack pine shoots collected at SSA-YJP; 9 trees x 1 branch x 2 replications. Trees were located about 250 m east of the hut and 80 m south of the access road. Branches were from the south side of trees and sunlit. Branches were collected from 1.5-2 m from the soil surface. Measured: 25-Jul-1994 Coordinated measurements of water potential, leaf optical properties, and shoot geometry on jack pine collected at SSA-YJP; 9 trees x 1 branch x 2 replications. Trees were located about 150 m east of the hut and 20-40 m north of the access road. Branches were from the south side of the trees and sunlit. Branches were collected from the top of the canopy. Measured: 29-Jul-1994 Coordinated measurements of water potential, leaf area, and leaf optical properties from aspen collected at SSA-YA; 3 trees x 3 branches x 3 replications from the top of the canopy. Branches were sunlit. Measured: 30-Jul-1994 Coordinated measurements of water potential, leaf optical properties, and shoot geometry from black spruce shoots collected at SSA-OBS; 3 trees x 3 branches x 3 replications. Samples were collected from the top of the canopy via the canopy access tower. Branches were sunlit. Measured: 02-Aug-1994 Coordinated measurements of water potential, leaf optical properties, and shoot geometry from black spruce shoots collected at SSA-OBS; 3 trees x 3 branches x 3 replications. Samples were collected from lower in the canopy (approximately 9 m from the soil surface) via the canopy access tower. Branches were mostly shaded. Measured: 04-Sep-1994 Coordinated measurement of water potential, leaf optical properties, and shoot geometry from black spruce shoots collected at SSA-OBS; 3 trees x 3 branches x 3 replications. Samples were collected from lower in the canopy (approximately 9 m from the soil surface) via the canopy access tower. Trees 1 and 3 are sunlit samples and tree 2 is shaded. Measured: 04-Sep-1994 Coordinated measurements of water potential, leaf area, and leaf optical properties from aspen collected at SSA-YA; 3 trees x 3 branches x 3 replications from sunlit branches at the top of the canopy. Measured: 17-Sep-1994 Coordinated measurement of water potential, leaf optical properties, and shoot geometry from black spruce shoots collected at SSA-OBS; 3 trees x 3 branches x 3 ages x 3 replications. Samples were collected from the top of the canopy via the canopy access tower. Measured: 11-Sep-1994 Coordinated measurements of water potential, leaf optical properties, and shoot geometry from jack pine shoots collected at SSA-YJP; 9 trees x 1 branch x 2 replications. Trees were located about 150 m east of the hut and 20-40 m north of the access road. Branches were collected from the top of the canopy. Measured: 14-Sep-1994 Coordinated measurements of water potential, leaf optical properties, and shoot geometry from jack pine shoots collected at SSA-YJP; 9 trees x 1 branch x 2 replications. Trees were located about 100 m east of the hut and 20-40 m north of the access road. Branches were from the south side of the trees and sunlit. Branches were collected from 2-3 m from the soil surface from trees near the canopy access scaffolding. 7. Data Description 7.1 Spatial Characteristics 7.1.1 Spatial Coverage Samples were collected from portions of the canopy at SSA-OBS, SSA-YJP, and SSA- FEN sites. The North American Datum 1983 (NAD83) coordinates for the sites are: Latitude Longitude ---------- ----------- SSA-FEN-FLXTR 53.80206 N 104.61798 W SSA-OA-FLXTR 53.62889 N 106.19779 W SSA-OBS-FLXTR 53.98717 N 105.11779 W SSA-YA-FLXTR 53.65601 N 105.32314 W SSA-YJP-FLXTR 53.87581 N 104.64529 W 7.1.2 Spatial Coverage Map Not applicable. 7.1.3 Spatial Resolution Shoot selection came from a branch approximately 30 to 70 cm long. 7.1.4 Projection Not applicable. 7.1.5 Grid Description Not applicable. 7.2 Temporal Characteristics Water potential measurements were made from 3 to 20 minutes after the branch was cut from the tree. 7.2.1 Temporal Coverage Branches were collected from 1530 to 0023 Greenwich Mean Time (GMT). Measurements were not made continuously (IFC-93 04-Aug-20-Aug-1993; IFC1-94 26- May-15 to Jun-1994; IFC2-94 21-Jul to 02-Aug-1994; IFC3-94 04-Sep to 14-Sep- 1994). 7.2.2 Temporal Coverage Map The following list gives the date, site, and type of samples collected: Date Site Species ---------- ------- ---------- 04-Aug-1993 SSA-FEN Jack Pine 04-Aug-1993 SSA-FEN Aspen 06-Aug-1993 SSA-FEN Black Spruce 16-Aug-1993 SSA-YJP Jack Pine 19-Aug-1993 SSA-FEN Aspen 20-Aug-1993 SSA-FEN Black Spruce 26-May-1994 SSA-YJP Jack Pine 29-May-1994 SSA-YA Aspen 01-Jun-1994 SSA-OBS Black Spruce 04-Jun-1994 SSA-YJP Jack Pine 06-Jun-1994 SSA-OA Aspen 07-Jun-1994 SSA-OBS Black Spruce 07-Jun-1994 SSA-YA Aspen 10-Jun-1994 SSA-YJP Jack Pine 15-Jun-1994 SSA-YA Aspen 21-Jul-1994 SSA-YJP Jack Pine 25-Jul-1994 SSA-YJP Jack Pine 29-Jul-1994 SSA-YA Aspen 30-Jul-1994 SSA-OBS Black Spruce 02-Aug-1994 SSA-OBS Black Spruce 04-Sep-1994 SSA-OBS Black Spruce 04-Sep-1994 SSA-YA Aspen 07-Sep-1994 SSA-YA Aspen 11-Sep-1994 SSA-YJP Jack Pine 14-Sep-1994 SSA-YJP Jack Pine 7.2.3 Temporal Resolution A typical water potential measurement required approximately 3 to 5 minutes. 7.3 Data Characteristics Data characteristics are defined in the companion data definition file (te12h2op.def). 7.4 Sample Data Record Sample data format shown in the companion data definition file (te12h2op.def). 8. Data Organization 8.1 Data Granularity All of the BOREAS TE-12 SSA Water Potential Data are contained in one dataset. 8.2 Data Format The files contain numerical and character fields of varying length separated by commas. The character fields are enclosed with single apostrophe marks. There are no spaces between the fields. Sample data records are shown in the companion data definition file (te12h2op.def). 9. Data Manipulations 9.1 Formulae Not applicable. 9.1.1 Derivation Techniques and Algorithms Not applicable. 9.2 Data Processing Sequence 9.2.1 Processing Steps Water potential for each tree was calculated based on separate shoot and/or branch measurements. 9.2.2 Processing Changes Not applicable. 9.3 Calculations 9.3.1 Special Corrections/Adjustments Not applicable. 9.3.2 Calculated Variables Not applicable. 9.4 Graphs and Plots None. 10. Errors 10.1 Sources of Error Some leakage of pressure from the stopper seal in the Precision Machine pressure chamber may have resulted in overestimates of water potential. There was confusion in distinguishing between the flow of the sap from the xylem and pitch vessels. Pitch is under less tension and exudes first when pressure is applied; thus, water potential may be underestimated if pitch was mistaken for sap. 10.2 Quality Assessment 10.2.1 Data Validation by Source None given. 10.2.2 Confidence Level/Accuracy Judgment None given. 10.2.3 Measurement Error for Parameters None given. 10.2.4 Additional Quality Assessments None given. 10.2.5 Data Verification by Data Center Data were examined for general consistency and clarity. 11. Notes 11.1 Limitations of the Data None given. 11.2 Known Problems with the Data None given. 11.3 Usage Guidance These data are acceptable for use with consideration of the above-mentioned known problems with the data and estimated errors. 11.4 Other Relevant Information Acknowledgment of other research staff who assisted in measurements: Liquang Chen, UNL graduate student Brian P. Lang, UNL undergraduate student Cynthia J.Hays, UNL Research Technologist Dr. Blaine L. Blad, Agricultural Department Head at UNL 12. Application of the Data Set Water potential is useful for studying the transpiration rates of plants. 13. Future Modifications and Plans None given. 14.Software 14.1 Software Development None given. 14.2 Software Access None given. 15. Data Access 15.1 Contact Information Ms. Beth Nelson BOREAS Data Manager NASA GSFC Greenbelt, MD (301) 286-4005 (301) 286-0239 (fax) beth@ltpmail.gsfc.nasa.gov 15.2 Data Center Identification See Section 15.1. 15.3 Procedures for Obtaining Data Users may place requests by telephone, electronic mail, or fax. 15.4 Data Center Status/Plans The TE-12 water potential data are available from the Earth Observing System Data and Information System EOSDIS Oak Ridge National Laboratory ORNL Distributed Active Archive Center DAAC. The BOREAS contact at ORNL is: ORNL DAAC User Services Oak Ridge National Laboratory (865) 241-3952 ornldaac@ornl.gov ornl@eos.nasa.gov 16. Output Products and Availability 16.1 Tape Products None. 16.2 Film Products None. 16.3 Other Products The data are available as tabular American Standard code for Information Interchange (ASCII) files. 17. References 17.1 Platform/Instrument/Data Processing Documentation Barbour, M.G., J.H. Burk and W.D. Pitts. 1980. Terrestrial Plant Ecology. The Benjamin/Cummings Publishing Company, Inc. 17.2 Journal Articles and Study Reports Sellers, P.and F. Hall. 1994. Boreal Ecosystem-Atmosphere Study: Experiment Plan. Version 1994-3.0, NASA BOREAS Report (EXPLAN 94). Sellers, P.and F. Hall. 1996. Boreal Ecosystem-Atmosphere Study: Experiment Plan. Version 1996-2.0, NASA BOREAS Report (EXPLAN 96). Sellers, P.and F. Hall. 1997. BOREAS Overview Paper. JGR Special Issue. Sellers, P., F. Hall, and K.F. Huemmrich. 1996. Boreal Ecosystem-Atmosphere Study: 1994 Operations. NASA BOREAS Report (OPS DOC 94). Sellers, P., F. Hall, and K.F. Huemmrich. 1997. Boreal Ecosystem-Atmosphere Study: 1996 Operations. NASA BOREAS Report (OPS DOC 96). Sellers, P., F. Hall, H. Margolis, B. Kelly, D. Baldocchi, G. den Hartog, J. Cihlar, M.G. Ryan, B. Goodison, P. Crill, K.J. Ranson, D. Lettenmaier, and D.E. Wickland. 1995. The boreal ecosystem-atmosphere study (BOREAS): an overview and early results from the 1994 field year. Bulletin of the American Meteorological Society. 76(9):1549-1577. 17.3 Archive/DBMS Usage Documentation None. 18. Glossary of Terms None. 19. List of Acronyms BOREAS - BOReas Ecosystem-Atmosphere Study BORIS - BOREAS Information System DAAC - Distributed Active Archive Center EOS - Earth Observing System EOSDIS - EOS Data and Information System FC - Field Campaign FEN - Nipawin Fen site FFC - Focused Field Campaign GMT - Greenwich Mean Time GSFC - Goddard Space Flight Center IFC - Intensive Field Campaign NASA - National Aeronautics and Space Administration NSA - Northern Study Area OA - Old Aspen OBS - Old Black Spruce OJP - Old Jack Pine ORNL - Oak Ridge National Laboratory PANP - Prince Albert National Park SA - Surface area of the leaf SSA - Southern Study Area TE - Terrestrial Ecology UNL - University of Nebraska - Lincoln URL - Uniform Resource Locator YA - Young Aspen YJP - Nipawin Young-Dry Jack Pine 20. Document Information 20.1 Document Revision Date Written: 08-Nov-1996 Last Updated: 06-Aug-1998 20.2 Document Review Date BORIS Review: 30-Apr-1997 Science Review: 23-Feb-1998 20.3 Document ID 20.4 Citation Please acknowledge the efforts of E.A. Walter-Shea, M.A. Mesarch, L. Chen, and L. Yang at UNL. 20.5 Document Curator 20.6 Document URL Keywords --------------- Water Potential Transpiration TE12_WaterPot 08/20/98