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Enabling better global research outcomes in soil, plant & environmental monitoring. ICT International PSY1 Leaf Psychrometer Water movement in plants Natural systems move matter across gradients: • Solutes (Concentration) • Height • Pressure Plants move water across a water potential gradient (Ψ) Water moves from high (soils) to low (leaves) water potential What is water potential (Ψ)? Integrated measurement of plant response to the environment Consider it to be equivalent to the blood pressure of a plant Humidity Temperature Soil moisture Ψ Solar radiation Soil nutrients What is water potential (Ψ)? Total plant water potential is defined as: Ψ = Ψp + Ψs + Ψm + Ψg Ψp = Turgor Pressure Ψs = Osmotic Potential Ψm = Matric Potential Ψg= Gravity Potential To measure plant water potential... Pressure chamber (bomb) In situ Psychrometers In Situ Psychrometer vs. Pressure chamber? In Situ Psychrometer Pressure chamber Dixon et al, (1984) Strong relationship between two instruments Pressure chamber After correction for sample temperature In Situ Psychrometer Dixon et al, (1984) PSY1 Leaf Psychrometer PSY1 Data Logger Standalone data logging system High precision 24-bit ADC circuit Internal micro SD card storage up to 64 GB Wireless (RF signal) and USB capabilities up to 250 line of sight Dynamic smart charging circuit using solar panels or DC power Rugged and water proof enclosure for all external environment conditions PSY1 Data Logger Wireless communication High temporal data collection (every 10 minutes) In Situ plant water potential measurements (leaf and stem) Stem Psychrometer Leaf Psychrometer Leaf Psychrometer Applications Leaf psychrometers have been tested on Capsicum Poplar Wheat Corn Leaf Psychrometer Installation 1. Select flat leaf surface for leaf psychrometer 2. Position leaf into the slot of the clamp 400 600 800 3. Select sandpaper grit based on thickness of leaf cuticle 4. Apply water on cuticle remover for lubrication Leaf Psychrometer Installation 5. Abrade surface of leaf in a circular motion 6. Apply silicon grease around psychrometersurface 0.5 mm 7. Spread silicon evenly on psychrometer surface perimeter (Approx. 0.5mm deep) 8. Insert psychrometer chamber into clamp, Secure by twisting the chamber on the leaf Why do you need to abrade leaf surface? Water vapour on the leaf diffuses through the substomatal cavity The cuticle layer varies across different plant species: Cuticle resistance effects the water potential measurement Leaf abrasion reduces cuticle resistance and improves water vapour diffusion in leaf Leaf abrasion reduces equilibration time of leaf and psychrometer chamber Grit Selection Plant Examples Grit Selection Cuticle Size Citrus Grasses Beans 400 Grit 600 800 Grit Thick Cuticle Thin Cuticle Level of Abrasion Heavy Abrasion Light Abrasion No Abrasion Wheat Application Wheat Application Wheat plants (4-weeks old) were grown in soil media Leaf psychrometers were installed on five leaves: • Wheat leaf 1/leaf 2 were adjacent leaves • Wheat leaf 3/leaf 4 were adjacent leaves • Control leaf had no abrasion treatment All wheat plants were irrigated together Leaf 4 Control leaf Leaf 2 Leaf 3 Leaf 1 Wheat Data Uninstallation of Leaf Psychrometer Leaf 1 (-3.94 MPa*) Installation duration: 5 days Leaf 2 (-1.23 MPa) Leaf 3 (-1.73 MPa) Installation duration: 7.5 days Installation duration: 7.5 days Leaf 4 (-0.90 MPa) Installation time: 7.5 days • Leaf 1 – Installation showed signs of failure after 4.5 days • Leaf 2 – Measurements continued to show reliable leaf water status after a week • Leaf 3 – Installation showed signs of failure after 4.5 days • Leaf 4 – Measurements continued to show reliable leaf water status after a week Wheat Data All psychrometers exhibited immediate response to irrigation, indicating installations are still reliable Wheat Data Leaf 2 and Leaf 4 still exhibit immediate response to irrigation. Installations are still reliable Leaf 1 and Leaf 3 showed no night time recovery and failed to respond to irrigation Corn Application Corn Application Three potted corn plants grown in a growth chamber for 4-weeks Each leaf used 600-grit sand paper to abrade the cuticle layer Two leaf psychrometers were installed per plant at different leaf heights (Top and Bottom) Corn 2 Corn 1 Corn 3 Corn Application Three potted corn plants grown in growth chamber for 4-weeks Each leaf used 600-grit sand paper to abrade the cuticle layer Two leaf psychrometers were installed per plant at different leaf heights (Top and Bottom) Top Leaf Corn 2 Corn 3 Bottom Leaf Bottom Leaf Corn 1 Top Leaf Corn Data Corn Data After a week of no irrigation, the soil looked dry. Soil Inspection After a Week of No Irrigation Before Irrigation After Irrigation Corn Data Plant water status indicates installations were still reliable after immediate response to irrigation Wheat and Corn Application Conclusions Reliable measurements from leaf psychrometer installations varied between species of plant: 1. Wheat leaves provided up to a week 2. Corn leaves may provide up to two weeks Abrasion of leaf is required to provide reliable leaf water status measurements Installation duration is dependent on a systematic abrasion technique Reliable measurements are determined based on response to night time recovery and/or irrigation Wheat Corn Rice Genotyping Example Rice genotyping with leaf water potential (LWP) Study conducted by Sibounheuang et al. (2006) demonstrated variations in LWP in 6 different rice genotypes using pressure chambers Objective of experiment: A. Determine genotype variations by measuring LWP at different leaf positions and plant sizes B. Examine whether genotype variations of different canopy size and water conductance are associated with LWP Experiment A Glasshouse experiment with automated temperature control system Six rice lines were tested and have known differences in LWP, osmotic potential, and osmotic adjustment from Jongdee (1998) Midday water potential was measured with pressure chamber at 4 positions: Tip, Sheath, Base, Stem during 10 day stress period Plant size were determined by xylem anatomy (vascular bundles and stem cross section area) Experiment A Results Genotype differences in midday LWP could be based on hydraulic conductance Leaf water potential was different among the 6 genotypes and demonstrated the same trend Leaf water potential and xylem area relationship showed genotypes with higher LWP showed larger xylem area Figure 3 from Sibounheuang (2006) B. Canopy size of genotypes associated with LWP Field experiment with rainout shelters to induce stress period of four rice lines Midday LWP was measured under 3 irrigation treatments (Irrigated, 14 and 18 days of stress) and 4 canopy sizes (control, 1/3 and 2/3 leaf removal and six tillers remaining) Midday water potential was measured at 4, 10 and 14 days after imposed stress Canopy size was measured by the number of vascular bundles Experiment B results Genotype variations of reduced canopy sizes (removing leaves/tillers) were not significantly reflected in LWP Differences in LWP among genotype variations were were not due to canopy size Leaf water potential expressed in different genotypes maintained the same trends, however differences were not due to canopy size or leaf area Figure 5 from Sibounheuang et a. (2006) Sibounheuang et a. (2006) Conclusions Genotype variation expressed in LWP and change in water stress were largely seen at leaf tip. Larger xylem size were associated with high LWP demonstrating a higher internal water conductance Hydraulic conductance of vascular bundles could have caused the genotype variation seen in rice. Leaf Psychrometer Conclusions PSY1 data logging systems provide wireless, continuous and automated measurements with a wide range of applications Leaf psychrometers demonstrated reliable plant water status for wheat and corn crops up to a week of continuous measurements Plant water status of rice crops have previously been monitored by the pressure chamber technique for genotyping. Leaf psychrometers provides the opportunity to continuously monitor leaf water status of rice in real time Postal: PO Box 503, Armidale, NSW 2350 Australia Address: 211 Mann St, Armidale, NSW, 2350 Australia Email: [email protected] Phone: +61 2 6772 6770