Water Relations

Water plays an important role in plants. For many, water comprises 90% or more of their weight. It serves to dissolve and bring in minerals from the soil, it is the solvent for sugars from photosynthesis being carried throughout the plant, it maintains the turgor pressure in the cells, and it cools the leaves as it evaporates. Today you will investigate some of the roles of water in plants.

I. Hydroponics

A. Observation. Plants are usually seen with their roots in soil. Soil probably provides the nutrients needed for plant growth.

B. Question. When plants have no soil available with the usual minerals bound to clay or humus particles, how much mineral nutrition is needed?

C. Hypothesis #1: Pure water is ideal for plants
Hypothesis #2: A certain amount of mineral nutrients is ideal for plants
Hypothesis #3: Plants can take as much mineral nutrient as you can give.

D. Prediction. Plants grown under various nutrient concentrations should show varying degrees of plant growth and development.

If H1 is true then plants grown in distilled water will grow best.

If H2 is true then some intermediate concentration of nutrients will produce the most growth.

If H3 is true then the highest concentration of nutrients will produce the most growth.

E. Experiment: Earlier in the semester, you planted radish seeds in perlite in plastic cups and added fertilizer at different concentrations until the cup was almost full. Now it is time to examine the plants to see the effect of different concentrations of nutrients in water on plants.

Locate the four cups that belong to you. They should be labeled 10x, 1x, 0.1x, and 0x. These numbers represent the concentrations of 20-20-20 fertilizer relative to the normal (1x) 9 grams per liter. Each solution was also given 1ml/l of MS-micronutrient Stock Solution.

If there are more than five plants in a cup, thin them down to the five most typical. Examine the plants and record the following information.

Please note, in filling in the charts,
Do not put a 0 when there is no plant to measure! Use an X instead!

	Concentration
	10x	1x	0.1x	0x
# Germinated Plants
Height of Plants (cm)
(Record Each One!)
Average Height of Plants Plants (cm)
Number of Leaves
(Record for Each Plant)
Average Number of Leaves
Hypocotyl Color
Cotyledon Color
True Leaf Color

F. Analysis: Calculate the averages requested in the table above. Circle the best colors!

G. Decision: Use the data from the experiment and the analysis above to decide about each hypothesis. Explain the basis of your decision.

HYPOTHESIS #1: Pure water is ideal for plants

is rejected         cannot be rejected	because plants in 0x concentration:
were taller         were shorter	than plants in other concentrations.
had more         had fewer	leaves than plants in other concentrations.

HYPOTHESIS #2: A certain amount of mineral nutrients is ideal for plants

is rejected         cannot be rejected	because plants in a middle concentration:
were taller         were shorter	than plants in other concentrations.
had more         had fewer	leaves than plants in other concentrations.

HYPOTHESIS #3: Plants can take as much mineral nutrient as you can give.

is rejected         cannot be rejected	because plants in 10x concentration:
were taller         were shorter	than plants in other concentrations.
had more         had fewer	leaves than plants in other concentrations.

II. Effect of nutrients on plant tissue

A. Observation. You have observed that plants do not grow well in high concentrations of nutrients. It might be easy to understand why some nutrients are needed and why distilled water would not support optimal growth.

B. Question. Why did high concentrations of nutrients inhibit growth? From your study of water relations with cells, you might know that distilled water is hypotonic to cells and leads to turgor pressure. Perhaps the high nutrient concentration inhibited growth by destroying turgor pressure. Was the 10x solution strongly hypertonic?

C. Hypothesis. The 10x fertilizer solution was strongly hypertonic.

D. Prediction. 10x fertilizer solution will cause plant tissue to lose water and therefore to lose weight.

E. Experiment. Rinse the four cups from Part I and refill them 2/3 full with the four fertilizer solutions: 10x, 1x, 0.1x, and 0x. Be sure to label the cups clearly!

Cut four slices of equal thickness (3-5mm) from a potato. Stack the slices and trim them so that all peel is removed. Continue to trim the stack of slices until the slices are of equal dimensions and will fit in the bottom of the cups.

Blot each slice dry with a paper towel. Weigh each slice individually keeping track of which slice is which. Put one slice in each cup of fertilizer solution.

	Fertilizer Concentration
	10x	1x	0.1x	0x
Initial Weight of Slice (g)

Wait one hour but swirl the cups periodically during the hour.

Blot each slice dry with a paper towel. Weigh each slice again and record as before:

	Fertilizer Concentration
	10x	1x	0.1x	0x
Final Weight of Slice (g)

Other Notes:

In trying to assess crispness, attempt to break each slice in half. Crispy slices break cleanly but with some force required, flaccid slices bend easily but do not break cleanly.

	10x	1x	0.1x	0x
Crispness	crispy moderate flaccid	crispy moderate flaccid	crispy moderate flaccid	crispy moderate flaccid
Color	dk blue mod blue lt blue white	dk blue mod blue lt blue white	dk blue mod blue lt blue white	dk blue mod blue lt blue white

Discard the potato slices, peels, and perlite into the compost area. Discard the cups in the trash.

F. Analysis: Calculate the percent weight change for each slice using the formula:

(final weight - initial weight) x 100 _______________________________ initial weight	round to whole percent

	Fertilizer Concentration
	10x	1x	0.1x	0x
Percent Weight Change

The concentration that is most hypotonic is _____x.

The concentration that is most hypertonic is _____x.

The most nearly isotonic concentration is _____x.

G. Decision:

The hypothesis: "The 10x fertilizer solution was strongly hypertonic" is:

rejected         not rejected

III. The effect of water level

A. Observation. Plants need water to survive.

B. Question. In a typical soil, how much water is needed?

C. Hypothesis. The more water is available, the better it is for the plant.

D. Prediction. Plants given unlimited water supply will grow more strongly than plants given a more restricted water supply.

E. Experiment. Earlier in the semester you planted radish seeds in pots. The pots were placed inside other empty pots to elevate them, and the stacks of pots were placed in a flat filled with water. Locate your pots in the greenhouse. If there are more than 5 plants in a pot, thin to the five most typical. Examine the plants and record the following information (remember when to use X!):

	Number of Outside Pots
	10	5	0
# Germinated Plants
Height of Plants (cm)
(Record Each One!)
Average Height of Plants (cm)
Number of Leaves
(Record for Each Plant>
Average Number of Leaves
Widest Leaf
(Record for Each Plant>
Average Widest Leaf
Hypocotyl Color
Cotyledon Color
True Leaf Color
Soil Moisture	soggy moist dry	soggy moist dry	soggy moist dry

F. Analysis. Calculate the averages requested in the tables above. Circle the best colors.

The tallest plants were found in:	soggy       moist       dry	soil.
The plants with the most leaves were found in:	soggy       moist       dry	soil.
The plants with the widest leaves were found in:	soggy       moist       dry	soil.
The plants with the best colors were found in:	soggy       moist       dry	soil.

G. Decision.

The hypothesis: "The more water is available, the better it is for the plant" is:

rejected       not rejected

Discard the plants and soil in the compost container.

Rinse out the pots, remove all tape, and leave them in the designated area.

Go back to the Course Schedule.