Split-Root Pea Biomass Allocation Study

ISEF Category: Plant Sciences

Subcategory: Growth and Development  ·  Difficulty: Intermediate  ·  Setup: School Lab  ·  Time: 1 to 2 Months

The Hook

Plants cannot move, but they can still make tradeoffs. If one side of a root system gets more water than the other, the plant may shift where it sends carbon, water, and growth. That makes split-root peas a smart way to test whether simple root-shoot models miss real plant behavior.

What Is It?

This project asks whether pea plants change how they build roots and shoots when only part of the root system gets extra water. In a split-root setup, one plant has its roots divided into two zones, so you can water each side differently. Think of it like giving one shoe a dry sock and the other a wet sock, then watching how the whole body responds.

The main outcome is biomass, which means how much dry plant material the plant makes. You can measure dry weight after harvest and compare root mass to shoot mass. Simple root-shoot ratio models assume plants adjust in a predictable way, but your data may show a more complex response, such as extra growth on the wetter side or a shift in total aboveground growth.

Why This Is a Good Topic

This is a strong science fair topic because you can change one clear variable, water distribution, and measure a real biological response with standard lab tools. It connects to drought stress, crop irrigation, and how plants manage limited resources. You can learn experimental design, destructive harvest methods, dry mass measurement, and basic statistics without needing a university lab.

Research Questions

• How does asymmetrical watering change the root-shoot biomass ratio in split-root pea plants?
• What is the effect of watering only one side of a split-root system on total dry biomass?
• Does the wet side of a split-root system produce more root biomass than the dry side?
• To what extent do split-root peas deviate from simple root-shoot ratio predictions under uneven watering?
• Which watering split, equal or unequal, produces the largest shoot biomass in pea plants?
• How does asymmetrical watering affect variance in biomass among replicate pea plants?

Basic Materials

• Pea seeds with similar starting size and age.
• Potting mix with consistent texture and drainage.
• Split-root pots or two connected containers with a divider.
• Standard nursery pots for control plants.
• Digital kitchen scale with 0.1 g accuracy.
• Paper bags or envelopes for drying plant tissue.
• Drying rack, food dehydrator, or school drying oven.
• Labels, waterproof marker, and masking tape.
• Measuring cup or graduated cylinder for watering.
• Ruler or meter stick for plant height tracking.
• Gloves and scissors for harvest.

Advanced Materials

• Analytical balance.
• Forced-air drying oven.
• Leaf area meter or flatbed scanner with ImageJ analysis.
• Soil moisture sensors for each root compartment.
• Controlled-environment growth chamber.
• Access to elemental analysis for tissue carbon and nitrogen.
• Statistical software for mixed models and effect size analysis.
• Root washing station with sieves and trays.

Software & Tools

• Google Sheets: Organizes harvest weights, growth measurements, and replicate comparisons.
• ImageJ: Measures leaf area and helps you track growth patterns from photos.
• R or RStudio: Runs statistical tests, graphs biomass ratios, and compares treatments.
• Jamovi: Offers a free point-and-click way to test group differences and variability.
• NIH ImageJ macros search: Helps you find workflow examples for plant image analysis.

Experiment Steps

1. Define the exact biomass outcome you will test, such as total dry mass, root mass, shoot mass, or root-shoot ratio.
2. Choose a split-root design that keeps the plant alive while giving each root zone a different watering treatment.
3. Set up control groups that rule out pot size, soil volume, and root crowding as causes of any biomass change.
4. Plan how you will dry, separate, and weigh roots and shoots so each plant is measured the same way.
5. Build a data table and analysis plan before planting so you can compare treatments with the right statistics.
6. Decide how you will check whether your results match, or break, a simple allocation model.

Common Pitfalls

• Mixing up wet weight and dry weight, which hides the real biomass response.
• Letting one split-root chamber hold more soil than the other, which confounds water effect with root space.
• Damaging fine roots during harvest, which can make the two sides look more different than they were.
• Using plants that started at very different sizes, which makes biomass comparisons noisy and unfair.
• Skipping enough replicates, which leaves you with patterns that look real but do not hold up statistically.

What Makes This Competitive

A stronger project goes beyond asking whether biomass changes. You can compare several watering asymmetries, track effect size, and test whether a simple allocation model fits your data. Strong entries also use clean controls, enough replicates, and a clear way to separate root response from shoot response. If you add a second trait, like leaf area or root distribution, your story becomes much stronger.

Project Variations

• Compare pea plants with bean plants to see whether different legumes allocate biomass differently under split-root watering.
• Test whether nutrient imbalance, instead of water imbalance, changes biomass allocation in the same split-root design.
• Add image-based leaf area measurements to see whether shoot size shifts before dry mass does.

Learn More

• USDA Plants Database: Use it to confirm pea species traits and growth information, and find it by searching the USDA site for Pisum sativum.
• NCBI Bookshelf: Search for free plant physiology chapters on water stress, biomass allocation, and source-sink relations.
• PubMed: Search review articles on split-root systems, drought stress, and biomass partitioning in legumes.
• MIT OpenCourseWare: Look for free plant biology and ecology lecture notes that explain plant growth and resource allocation.
• USGS Water Science School: Use it to review how plants interact with water availability and soil moisture concepts.