In this experiment, which will take 4 to 5 weeks to complete, you will make qualitative and quantitative observations on the effects that deficiencies of various mineral salts have on the growth of sunflower (Helianthus ssp) plants.
Introduction
All organisms require minerals in order to complete their life cycles. For example, you know that animals, including humans, require calcium and iron salts. Plants also must acquire these and other minerals. Some compounds required by plants for photosynthesis (CO2) are found in the air and soil and usually do not limit plant growth. Oxygen (required by plants for respiration) is also found in the air and in well-aerated soil. However, mineral ions needed for normal plant metabolism, including photosynthesis and respiration, are found dissolved in soil water. Occasionally, soils may be deficient in one or more minerals, and some mineral deficiencies may have profound effects on plant growth, plant morphology, and yield of economically important plant parts such as fruits and seeds. One way to assess the effects of mineral deprivation is to grow a representative plant species in a non-soil matrix and to exclude one nutrient only. The effects of this regime are then compared to those seen in control plants grown in a medium containing all nutrients.
The first week, you will plant seeds in washed sand or perlite and make up stock solutions of mineral salts. Next week you will combine and dilute the stock solutions to make the treatment solutions, each of which lacks a particular mineral element, or has a particular concentration of a mineral nutrient. Your lab instructor will give you the specific instructions for your group: Write them down! The seedlings will be then be transplanted to beakers containing the mineral nutrient solutions. This type of growth is called hydroponics. You will make qualitative observations on the progress of the plants’ growth, and after 2 weeks you will make several quantitative measurements of plant growth.
PROCEDURE
Your lab instructor will assign seeds and treatments to groups of 3-4 students. Seeds will be planted in sand or perlite, watered, and placed on a light table in the greenhouse. Follow instructions for planting depth and watering for your particular seed type.
Now make up the stock mineral solutions. There are eight different solutions that need to be made, plus a micronutrient solution that has already been prepared. Pick up one of the labeled storage bottles, and then make up the 1M solution by dissolving the appropriate amount of salt in enough distilled water to reach a volume of 100 ml. Why is it important to use distilled water?
……………………Approximately 1 week later……………………………
Today you will place the germinated seedlings into the mineral solutions. One set of controls will receive the complete nutrient solution; the other controls will receive distilled water only. What kinds of predictions would you make about the growth of the control plants?
Each group will be responsible for all treatments. Label the beakers, get a plastic bottle to make up solutions, and use the table on the next page to determine how much of which 1M solution is required. Add the stock solutions to enough distilled water to reach a final volume of 1 liter. You may then need to add appropriate amounts of your assigned nutrient: your lab instructor will explain, and you should write down the instructions. Be careful not to mix up pipettes. Make sure you mix the solution well before pouring it into the beakers. Each beaker holds about 800 ml, so you may have to make the solutions twice. Save the remainder to top off the beakers as your plants use the solutions.
Now gently remove the seedlings from the flats and place them into a dish with distilled water. Gently swish the roots around in the water to dislodge the sand particles. Be sure to never let the roots dry out. Rinse in clean distilled water and place 3 plants in each beaker. To support the plants in the beaker, for each plant, carefully cut an “X” in the lid and bend back the points to make a hole. Wrap a small piece of cotton around the hypocotyl to protect it, carefully insert the seedlings into the holes, and place the lid on the container. Try not to get the cotton wet because molds growing in the wet cotton can damage plant stems. Be very careful not to damage the plants by squeezing the stems.
We will arrange the plants in rows by treatment so it will be easier to make observations during the next two weeks. A more rigorous experiment would probably involve random placement of the plants under the grow lights; why do you think this is so? Another good observation for the lab report!
You are responsible for observing all treatment and control plants, not just the ones you transplanted. You will measure plants 1 time per week. Look closely! Compare the treatment plants to the control plants. Are there differences in leaf morphology, leaf color, length of stem between leaves, thickness of leaves, etc.? Don’t forget to look at the roots! Refer to pages 72 – 25 in your textbook to help you know what to look for. Be sure to record your observations; you will want to summarize them in your lab report.
Table 1. Milliliters of stock solution added per 500 ml d H2O
| H2O | Complete | minus Ca | Minus Mg | minus N | minus Fe | minus P | |
| 1. Ca(NO3)2 | – | 2.5 | – | 2.5 | – | 2.5 | 2.5 |
| 2. KNO3 | – | 2.5 | 2.5 | 2.5 | – | 2.5 | 2.5 |
| 3. MgSO4 | – | 1.0 | 1 | – | 1 | 1 | 1 |
| 4. KH2PO4 | – | 0.5 | 0.5 | 0.5 | 0.5 | 0.5 | – |
| 5. NaNO3 | – | – | 5 | – | – | – | – |
| 6. Na2SO4 | – | – | – | 1 | – | – | – |
| 7. CaCl2 | – | – | – | – | 2.5 | – | – |
| 8. KCl | – | – | – | – | 2.5 | – | 0.5 |
| 9. FeEDTA | – | 0.5 | 0.5 | 0.5 | 0.5 | – | 0.5 |
| 10. Micronut. | – | 0.5 | 0.5 | 0.5 | 0.5 | 0.5 | 0.5 |
…………………………….3-4 weeks later…………………………
You have been making qualitative observations on the mineral nutrition experiment for 2 weeks; now you will take some quantitative measurements and terminate the experiment. Make the following measurements for the treatment your group planted. Record your measurements in your notebook, and then transfer them to a data sheet. The raw data will go into the large space (write legibly and in ink; this sheet containing data for the whole class will be photocopied and given to you before you leave).
Height: For each plant, measure the distance in mm from the cotyledons to the position of the apical meristem
Leaf number: For each plant, count the total number of leaves (excluding cotyledons) whose blades are at least 10 mm in length. Include dead leaves.
Weight: Carefully tear apart the cardboard lid and remove the cotton from around each plant. Blot off the excess water from the roots with a paper towel, and record the wet weight of each plant to the nearest 0.01 g.
Calculations
You will get a copy of the data sheet, containing only raw data. Calculate means for height, leaf number, and weight for each treatment. In order to determine whether means of treated plants differ significantly from control means, you should perform two sample t-tests. You can simply put an asterisk next to all means that differ significantly.
Writing the lab report
You are responsible for analysis of ALL treatments, regardless of which solution you were assigned. You will each write an introduction, methods, results and literature cited only. Put the quantitative results in a table or graph, and cite that figure in your results section. Of course, you will not repeat the numbers from the figure in your text. Do not include the raw data in your results section. You will also have qualitative observations in your results. You should include results from all the different types of plants in your lab report. Be sure to include at least 2 citations from the primary literature.
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