NAME ____________________________
Honors Laboratory
EFFECT OF SALINITY ON
SEED GERMINATION AND ROOT GROWTH
INTRODUCTION
Many of you who live in coastal cities hear more and more concerning the intrusion of salt into
the drinking water supply. In a more natural setting, the coastal areas are subjected to changes in
salinity on a regular basis. Hurricanes commonly bring salt water several miles inland, killing
many plants, not due to the winds, but due the salinity. The marine environment supports a
completely different flora. Plants that grow near the ocean must be able to withstand the osmotic
effects of water loss.
Seawater is about 3.3% salts, including NaCl (Sodium Chloride) as well as other molecules.
Interestingly enough, essentially all freshwater organisms cannot withstand salinities above 5%
and many plants cannot tolerate salinities of 2.5%. In this lab we will look at the effect of
salinity on the seed germination and early development of radish. This can be easily done by
using various salinity solutions, made by dissolving various amounts of table salt (NaCl) in water
and observing the germination and root development.
OBJECTIVES
1. Determine the maximum salinity radish seeds can withstand and yet germinate.
2. Determine the effect of salinity on early seedling root elongation of radish.
3. Statistically and graphically analyze experimental data.
PROCEDURE
To see the real effect of salinity has on reducing seed germination rates, we must also note the
germination rate of seeds in water without any salt, the control. In this experiment, tap water
will be used as the control.
1. Obtain four petri plates; label with the various salinities we will use. These salinities are:
0%, 1.0%, 2.0%, and 3.0%. Place several layers of filter paper (or paper towels) in the
bottom of each of the petri dishes. Be sure to mark plates with their corresponding salinity.
Saturate the filter paper in one dish with tap water and the others with the various salinity
solutions. Do not leave excess standing water in the dishes.
2. Add 25 radish seeds to each plate; be sure to spread them evenly.
3. After 5-7 days observe the seeds and seedlings. Both the number of seeds germinating and
the length of the primary root of the germinating seed need to be determined. Make ALL root
measurements on the same day. That is, DO NOT measure the control and 2% salinity
seedlings one day and the other seedlings the next day. Record the data in TABLE 1.
Salinity effect on germination
ANALYSIS OF DATA
Summarize the data in TABLE 2 by calculating the mean and standard deviation. We can use a
simple computer program make this process relatively quick. The mean, or average is a measure
of what a typical measurement would be. The standard deviation is a measure of how much
variation there is around the average.
Make two (2) line graphs to visually analyze the data.
 First, graph the salinity (x-axis) vs. the percent germination (y-axis) for both radish and corn.
Code the two different species and plot on the same graph.
 Second, plot the salinity vs. the average root length. Remember to label each graph with a
title.
NOTE #1:
Graphs commonly allow one to easily observe the results, especially if there are lots of numbers.
Two basic types of graphs exist, line and bar. Line graphs are used when both variables (what
are to be graphed on the x- and y-axis) are of data that may be of any value (continuous), such as
distance measurements. Bar graphs are used when one of the variables only fits into a finite
number of categories (discontinuous), such as colors or species names. Since salinity can
theoretically be of any value, we have continuous data and would construct a line graph.
NOTE #2:
To visually see variation some graphs commonly include the standard variation as a vertical bar.
Each point would then represent the mean plus or minus the standard deviation. For example
one might have a root length of 11.2 +/- 0.6 mm; the dot would be at 11.2 and a vertical line
would extend from 10.6 (11.2 - 0.6) to 11.8 (11.2 + 0.6). We will not do this on our graphs, as it
does take much work.
Honors lab. pg. 3
TABLE 1: Root lengths (mm) of seedlings in various salinities. Record only data that you
actually measured and/or calculated.
Seed number
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
0% (control)
1%
2%
3%
TABLE 2: Summary effect of salinity on seed germination and root development. Standard
deviation can be calculated on a spreadsheet program.
SALINITY
0% (control)
1.0%
2.0%
3.0%
PERCENT
GERMINATION
AVERAGE ROOT
LENGTH (mm)
STD DEVIATION OF
ROOT LENGTH
Salinity effect on germination
QUESTIONS
1. What do you conclude is the highest salinity that will allow for normal germination and early
growth of the seeds?
2. Are seed germination and root growth affected in the same way relative to percentages
allowing the processes to occur?
3. In the real world under natural conditions, where would soil become too saline for crop
growth? (search the Internet if needed)
4. In the real world, where have humans modified the soil to make it too saline for crop growth?
(think globally)
5. We shouldn’t use information from this lab to make policy changes for the state or country.
Describe, using Park’s VooDoo Science terms, the problems that would develop from such an ill
advised undertaking.