google.com, pub-6546753431946252, DIRECT, f08c47fec0942fa0
top of page
Search

AGR4301 Advanced Crop Physiology Laboratory Manual



1. INTRODUCTION

Duckweed (Lemna spp.) is a fast-growing aquatic plant widely used as a model organism in plant physiology due to its rapid vegetative reproduction, simple structure, and high sensitivity to environmental changes. Its small size and short life cycle make it particularly suitable for studying physiological responses under controlled experimental conditions.


These short experiments are designed to target improvements in crop performance at the cellular level, which will directly translate into enhanced plant growth and yield. Specifically, the experiments focus on two critical organelles: the chloroplast and the mitochondrion. The chloroplast is responsible for photosynthesis, where light energy is converted into chemical energy, while the mitochondrion plays a central role in cellular respiration and energy production.


Environmental factors such as light intensity, carbon dioxide (CO₂) concentration, and nutrient availability directly influence the efficiency of these organelles. By manipulating these conditions, this experiment series aims to understand how cellular processes can be optimised to improve overall plant productivity.

Through these investigations, students will gain insights into how external environmental factors regulate internal physiological mechanisms, ultimately linking cellular function to whole-plant performance and crop yield improvement.

 

2. OBJECTIVES

i. To evaluate the effect of light and nutrient sources on duckweed growth and physiological responses.

ii. To determine the effect of elevated CO₂ concentration on duckweed performance.

iii. To investigate the interaction between environmental factors (light, CO₂, and nutrients) on plant physiological responses.

 

3. GENERAL MATERIALS AND EQUIPMENT

  • Duckweed (Lemna spp.) 

  • Transparent plastic cups (150–200 mL capacity)

  • Paper cups (light shielding)

  • Ruler or imaging device

  • Camera or smartphone

  • Analytical balance

 

EXPERIMENT 1: THE IMPACTS OF LIGHT CONDITIONS AND NUTRIENT SOLUTIONS ON DUCKWEED GROWTH AND PHYSIOLOGICAL RESPONSES

 

OBJECTIVE 

To determine the effect of different light quality, intensity and type of nutrient solutions on duckweed biomass accumulation and physiological responses

 

HYPOTHESIS

i. Duckweed cultivated under LED lights will exhibit a higher growth rate and greater biomass accumulation compared to those grown under indirect natural sunlight.

ii. Different nutrient sources will result in significantly different growth rates in duckweed due to variation in nutrient availability and form.

 

EXPERIMENT VARIABLES

Constant Variable (CV): Duckweed accession (Sampled from Central Perak).

Manipulated Variable (MV): Light source and Nutrient solutions

Responding Variable (RV): Growth and physiological performance

 

EXPERIMENT TREATMENTS

Factor 1: Type of light source

L1: LED light source

L2: Natural sunlight

 

Factor 2: Nutrient solutions

L1: Blood meal solution (1% wt/vol)

L2: Feather meal solution (1% wt/vol)

L3: Urea solution (1% wt/vol)

L4: Christmas Island Rock Phosphate (CIRP) solution (1% wt/vol)

L5: White sugar solution (1% wt/vol)

L6: Malacca palm sugar solution (1% wt/vol)

L7: Pond water (Control)


No.

Treatment 1:

Light source

Treatment 2:

Nutrient solutions

Treatment combination

1

LED light (L)

Blood meal (B)

L:B

2

Natural sunlight (N)

Feather meal (F)

L:F

3

 

Urea (U)

L:U

4

 

CIRP (C)

L:C

5

 

White sugar (W)

L:W

6

 

Malacca palm sugar (M)

L:M

7

 

Pond water (P)

L:P

8

 

 

N:B

9

 

 

N:F

10

 

 

N:U

11

 

 

N:C

12

 

 

N:W

13

 

 

N:M

14

 

 

N:P

 

 

 

“:” means combine


MATERIALS

  • LED grow lights

  • Duckweed (Lemna sp.) 

  • Transparent plastic cups (150–200 ml capacity)

  • Paper cups (light shielding)

  • Nutrient solutions (blood meal, feather meal, urea, CIRP, white sugar, Malacca palm sugar, pond water)

  • Ruler or imaging device

  • Camera or smartphone

  • Analytical balance

  • Light meter

  • Tray


EXPERIMENTAL LAYOUT & DESIGN

The experiment was arranged in a Nested Randomised Complete Block Design (NRCBD) to account for spatial and environmental variability. Two blocks were established to represent vertical environmental gradients (e.g., temperature, humidity, and light distribution).

 

Within each block, light condition (LED and natural sunlight) was assigned as the primary grouping factor based on fixed spatial locations. Experimental trays were nested within each light condition and block, serving as independent replicates.

 

Within each tray, the seven nutrient treatments were randomly assigned to individual cups, resulting in a hierarchical structure where cups were nested within trays, and trays were nested within light conditions and blocks.

 

This design minimises pseudo-replication by treating trays as the true experimental units for the light factor, while nutrient treatments are evaluated at the cup level within each tray.

Component

Specification

Details

Blocks

2 Vertical Blocks

Controls for spatial variance (e.g., temperature/humidity gradients).

Main Factor A

Lighting (2 levels)

LED Light Source vs. Natural Sunlight.

Main Factor B

Nutrients (7 levels)

Blood meal, Feather meal, Urea, CIRP, Pond water, White sugar, Palm sugar.

Replicates

3 Trays

Each Block/Light combination contains 4 independent trays.

Total Treatments

14 Combinations

Calculated as: 2 Light levels x 7 Nutrient levels.

Quantitative Breakdown (n-value)

  • Experimental Unit: One individual cup containing Lemna.

  • Cups per Tray: 7 (One for each nutrient treatment).

  • Trays per Light Source: 8 trays (2 Blocks x 3 Replicates).

  • Total Experimental Units (n): 84 Cups

    • Calculation: 2 Light Sources x 6 Trays x 7 Cups = 84.

 

PROCEDURES


A. Preparation of Nutrient Solutions (1% wt/vol using Pond Water)

  1. Collect pond water from a single source before use to ensure consistency across treatments

  2. Prepare 1% (wt/vol) nutrient solutions (e.g. 1 g of material in 100 mL of pond water).

  3. Prepare the following solutions:

    • Blood meal solution (1% wt/vol)

    • Feather meal solution (1% wt/vol)

    • Urea solution (1% wt/vol)

    • CIRP solution (1% wt/vol)

    • White sugar solution (1% wt/vol)

    • Malacca palm sugar solution (1% wt/vol)

  4. Stir each solution thoroughly until evenly mixed.

  5. Use pond water without any addition as the control treatment.

 

B. Preparation of Experimental Units

  1. Label all cups according to treatment and block (e.g., B1–L:B, B2–N:U).

  2. Nest each transparent plastic cup inside a paper cup to prevent lateral light penetration.

  3. Add approximately 150 mL of the respective nutrient solution into each plastic cup.


C. Duckweed Inoculation

  1. Select healthy, uniform duckweed fronds

  1. Gently rinse with clean water to remove contaminants (if necessary).

  2. Inoculate each cup with:

    • 3 similar-sized duckweed fronds


D. Experimental Setup (Nested Randomised Complete Block Design (NRCBD)

1.   Arrange the experiment according to a Nested RCBD with two blocks:

o   Blocks (2): Represent spatial/environmental gradients (e.g., temperature, humidity).

o   Primary grouping factor: Light condition (LED vs. natural sunlight), assigned based

on fixed locations.

o   Replicates: Three trays are nested within each light condition and block, serving as

independent experimental units.

o   Nested factor: Seven nutrient treatments are applied to cups within each tray.

2.     Placement of experimental units:

o   LED treatments: Standardise the photoperiod (e.g., 12 hours light / 12 hours dark)

o   Natural light treatments: Place trays near a window receiving indirect sunlight,

ensuring minimal exposure to direct midday light.

3.     Within each tray:

o   Randomly assign the seven nutrient treatments to individual cups.

o   Ensure uniform spacing between cups to minimise competition and shading effects.

4.     General arrangement control:

o   Maintain consistent distance between trays and light sources within each light

condition.

o   Avoid cross-shading and ensure similar airflow conditions across all treatments.


E. Maintenance

1.  Maintain water levels by topping up with nutrient solution to the top line of the cup every two days to account for evaporation.

2.  Conduct the experiment for 10 -14 days

 

 

DATA COLLECTION

Data should be recorded every 2–3 days throughout the experimental period.

A. Growth Monitoring (Non-Destructive)

At each sampling interval, record the following:

  • Aerial Image of Duckweed

    • Capture a clear top-view (aerial) photograph of each sample.

    • Include a scale reference (e.g., ruler or known diameter object) in every image.


  • Ensure consistent:

    • Camera height

    • Lighting conditions

    • Background (preferably plain and contrasting)


  • Frond Area Coverage

    • Analyse images using the Easy Leaf Area application to estimate surface coverage.

    • Record the percentage of area covered by duckweed.

·       

  • Light Measurement (GPS Status App)

Open the GPS Status & Toolbox app.

Measure the light intensity at the level of your plants.

Record the value in Lux.


Required Tools for Image Analysis and Light reading



B. Final Day Measurements

At the end of the experiment, perform the following measurements:

  • Physiological Measurements

    • Measure photosynthetic parameters using the LI-6800 Portable Photosynthesis System.

  • Fresh Weight

    • Gently collect duckweed samples.

    • Remove excess surface water using tissue paper.

    • Weigh immediately to obtain fresh biomass (g).

  • Dry Weight

    • Dry samples in an oven at 60–70°C for 48 hours or until constant weight.

    • Record dry biomass (g)


Comments

bottom of page