Drought Priming and Leaf Temperature Response

ISEF Category: Plant Sciences

Subcategory: Plant Physiology  ·  Difficulty: Intermediate  ·  Setup: School Lab  ·  Time: 1 to 2 Months

The Hook

Plants do not wait passively for drought to hit. Some can "remember" a mild stress and react faster later, almost like a fire drill. You can test that memory with leaf temperature, because closed stomata usually make leaves warmer. That gives you a way to track plant response without tearing the leaf apart.

What Is It?

This project looks at drought priming, also called hardening. You give a plant a mild water shortage first, then later expose it to a stronger drought. If the plant responds faster the second time, it may close its stomata sooner. Stomata are tiny pores on leaves that act like vents. They open for carbon dioxide and close to save water.

Think of stomata like windows in a house. On a cool day, you might leave them open. During a heat wave, you close them faster because you already know what is coming. In plants, faster stomatal closure can raise leaf temperature. A thermal camera can pick up that change, so you can compare primed and unprimed plants without complex lab gear.

Why This Is a Good Topic

This is a strong science fair topic because you can test a real plant stress response with a clear measurement signal. You are not just asking whether plants survive drought. You are asking whether prior stress changes the speed of their response, which makes the question more scientific and more interesting. It connects to water use, crop resilience, and climate stress, and you can study it with simple plants, careful controls, and basic thermal imaging.

Research Questions

• How does mild drought pre-exposure change the speed of leaf temperature rise during later severe drought?
• What is the effect of drought hardening on the maximum leaf temperature reached under water stress?
• Does plant species change the size of the priming effect on stomatal-closure response?
• To what extent does repeated mild drought improve thermal recovery after rewatering?
• Which watering history gives the strongest leaf-temperature signal during drought challenge?
• How does time since hardening affect the strength of the primed response?

Basic Materials

• Potted fast-growing plants such as bean, basil, or radish seedlings.
• Identical plant pots with drainage trays.
• Potting soil with the same mix for every pot.
• Measuring cup or graduated cylinder for consistent watering.
• Digital kitchen scale with 0.1 g accuracy.
• FLIR One smartphone attachment or similar thermal camera.
• Smartphone with camera app and note-taking app.
• Labels or plant tags.
• Ruler or measuring tape.
• Light source with stable indoor placement.
• Notebook or spreadsheet for tracking plant health and temperature readings.

Advanced Materials

• Gas exchange system for stomatal conductance measurement.
• Chlorophyll fluorescence meter.
• Infrared thermometer for spot checks and calibration.
• Environmental chamber or controlled growth space.
• Soil moisture sensors or a volumetric water content probe.
• Data logger for continuous temperature and humidity tracking.
• Leaf porometer.
• Image analysis software for thermal image quantification.
• Analytical balance for pot mass tracking.
• Controlled irrigation setup for repeated treatment timing.

Software & Tools

• ImageJ: Measures leaf area and helps compare thermal regions across plants.
• Google Sheets: Organizes plant mass, temperature, and treatment timing in one place.
• R: Runs statistics, graphs response curves, and tests whether primed plants differ from controls.
• Python: Automates thermal image cleanup and batch analysis when you have many leaves.
• FLIR Tools: Reviews thermal images and exports temperature data from the camera.

Experiment Steps

1. Define one plant species, one drought stress plan, and one thermal signal you will track.
2. Choose a control group and a primed group so you can compare watering history.
3. Decide how you will standardize plant size, light, and pot moisture before the drought challenge.
4. Build a measurement plan that turns thermal images into a repeatable temperature metric.
5. Plan the comparison you will use to judge response speed, not just final heat level.
6. Choose the statistics you will use to test whether primed plants respond differently from controls.

Common Pitfalls

• Letting leaf angle change between photos, which can make the thermal signal look like a drought effect when it is really a camera angle effect.
• Mixing plants of very different sizes, which can hide a real priming response behind growth stage differences.
• Using room light or airflow that changes during the trial, which can shift leaf temperature for reasons unrelated to stomata.
• Defining drought only by calendar time instead of pot mass or soil moisture, which makes the stress level inconsistent.
• Comparing a single snapshot instead of a response curve, which can miss the faster timing that priming is supposed to change.

What Makes This Competitive

A strong project here goes beyond simple before-and-after photos. You would show a clear response curve, match plants carefully, and use a control that rules out size, light, and humidity effects. You could also compare species, ask whether the priming fades over time, or test whether thermal change matches another measure of stomatal behavior. That kind of design turns a neat demo into a real physiology study.

Project Variations

• Test whether drought priming differs between sun-grown and shade-grown plants.
• Compare thermal response in seedlings versus mature plants under the same drought history.
• Add a recovery phase and measure whether primed plants cool faster after rewatering.

Learn More

• USDA Plant Hardiness and Water Stress resources: Search USDA pages and extension fact sheets on drought stress, stomata, and plant water relations.
• NOAA Climate.gov: Use background articles on drought, heat stress, and plant water demand.
• NASA Earth Observatory: Read articles on plant stress, land surface temperature, and remote sensing of vegetation.
• PubMed: Search review articles on drought priming, stomatal conductance, and plant stress memory.
• MIT OpenCourseWare: Find plant biology and physiology lecture notes for background on transpiration and stomatal control.