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variety of environmental factors such as light intensity, photo
period, light quality (spectral composition), temperature,
temperature fluctuations, nitrates, O_{2} and CO_{2} levels, pH, moisture, etc.
(Silvertown 1982; p.31). Germination, which is the process of birth
for seed plants, depends primarily on the availability of water
(Blundon 1994). If the temperature is favourable, the dormant embryo
of the seed begins to grow (Blundon 1994). The rate of germination of
seeds, of seedling growth, and of root growth depends on the soil
temperature, being negligible below a certain temperature, rising to
a maximum and then falling off as the temperature rises (Russell
1973; p.401).
In accordance with the duration of the life cycle, plants are divided
in two groups: annuals and perennials. Annuals, like oats, complete
their entire life cycle in a single year, while perennials, like
bromus, can live for more than a single year once they have reached
sexual maturity (Blundon 1994). Because of their short life
(semelparity), annuals must have a successful reproduction in a
limited amount of time, and their seeds must germinate rapidly
(Blundon 1994). Consequently, the number of germinated seeds should
be important in despite of the fact there are unfavourable
environmental conditions such as a low temperature, and initial root
growth should be rapid (Blundon 1994). In the case of perennials, if
conditions are favourable and vegetative growth is adequate, the
mature individual may reproduce for a number of years (iteroparity)
(Blundon 1994). Even if conditions are unfavourable for seeds
production, reproduction can still occur vegetatively and mature
individuals can survive in a state of dormancy until favourable
conditions return (Blundon 1994). Perennials seeds should germinate
more slowly, have a lower frequency of germination and a slower
initial root growth under a variety of conditions, and be more
restricted by low temperature than annuals seeds when water is not
limiting (Blundon 1994). This experiment was embarked upon the
intention to know if these hypotheses are verifiable and conclusive.
The objective of this experiment was to analysis an annual and a
perennial plant under different temperatures and water
potentials.
January 20 to February 3, 1994, the experiment was conceived in a biology laboratory at Camosun College during a class period. The technique of collecting data and the used material were very simple. In conformity with the tables one to four, the experimentation was divided in two parts, the preparation of the laboratory and the counting of germinated seeds. During the first week, twelve petri dishes, containing each of them a filter paper, distilled water (water potential = 0 bars) or mannitol (water potential = 15 bars), and thirty seeds of the appropriate species (Oats or Bromus), were put in a cardboard boxes with the other groups. By adding mannitol to pure water, the concentration of free water is reduced and negative pressure (suction) must be applied by the seed to imbibe water (Blundon 1994). Afterwards, these cardboard boxes were put in a growth chambers (= incubators for 10^{o}C and 16^{o}C dishes, a lab drawer for 22^{o}C). During the two second weeks, germinated seeds, root length, and viability of ungerminated seeds were counted. The test of viability of ungerminated seeds consisted to place a drop of 0.5% triphenyl tetrazolium on seeds, which were cut in half lengthwise, to obtain a red colour, indicating a positive test after one or two days. Details of the method are given in Blundon (1994).
Obtained data were compiled in the tables one to four. Table one and table two represent the germination frequency after one and two weeks. ¯x is the mean of the replicate number and % is the percentage of germination frequency. The summary about all treatments combined shows S,¯x and P(=%). S means the sum of all germinated seeds, ¯x is the total mean of germinated seeds and P(=%) is the total percentage of germinated seeds. Below this summary, z is the z test and d.f. is the degrees of freedom. The z test is:
P, which is the number of germinated seeds (X) divided by the total number of seeds (n) for one species or both species, is the proportion of units in the population which have attribute to the species, and q is the proportion of units in the population which do not have attribute to the species (Satin 1993; p. 63).
The degree of freedom is:
N is the number of observations in the sample {2*(6*6)=72} for both species. Table 3 represents the root length (cm) after two weeks. The methods of calculation are similar to tables one and two. The only difference is the presence of the S^{2}, N and t. S^{2} , or the variance, is:
N is the number of observations in the sample for each species. "t" or ttest (tetrazolium test) is:
"This test involves calculating a test statistic
(t) and comparing the value we get to the appropriate critical value
in the ttable, based on the degrees of freedom (which depends on our
sample sizes) and the significance level we choose" (Blundon 1994).
Table
4, which represents the viability of
ungerminated seeds after two weeks, uses methods of calculation
similar to the other tables.
Fig. 1 to 3, which represent all data obtained in the tables one to
four, show the trends of each table (germination frequency, root
length and viability) in function of the water potential and the
temperature. It is easy to remark in the first graph (Fig. 1) that Bromus has a germination frequency higher than Oats.
Oats and Bromus have a germination frequency for a negative water
potential lower than for a water potential to 0. Oats and Bromus have
a germination frequency that increases with a growing temperature. In
the second graph (Fig. 2), Oats' roots are longer than Bromus' roots. The roots
length decreases with a negative water potential and increases with a
growing temperature. In the last graph (Fig. 3), the viability of ungerminated seeds is higher for Oats
than for Bromus. The viability decreases with a growing temperature,
increases with a negative water potential for Bromus, and decreases a
little bit with a negative water potential for Oats.
Finally, Table
5 and Fig. 4 represent least squares linear regression of germination
frequency. "The usual way of determining the effect of an
environmental variable like temperature on a biological function like
germination is through the use of regression analysis" (Blundon,
1994). The method of least squares gives an equation for a straight
line according to:
where: a = the point of intercept on the Y axis (i.e., Y when X =
0)
b = the slope of
the line, a change in Y per unit of change in X (in
this case, how many more seeds germinate in a sample of 30
per degree of increased temperature or vice versa)
x = temperature
and
y = number of
seeds germinated in sample of 30.
The equations for a and b are:
The resultant straight lines can be plotted by substituting two values of X into the equation y = a + bx, calculating and plotting expected Y values for these values of X, and drawing a straight line between them. The result of this straight line is the Fig. 4, which represents the number of germinated seeds in function of temperature. The straight line for oats (y= 5.06  0.17x) is a negative line and the straight line for Bromus (y= 5.12 + 1.26x) is a positive line. Bromus has the greatest slope for the regression of germination frequency on temperature. Details of the method are given in Blundon (1994).
According to Blundon (introduction), this experiment was not conclusive because the germination frequency of the perennial Bromus was higher than the annual Oats (Fig. 4). On the other hand, Oats' roots were longer than Bromus and the viability of ungerminated seeds was better for Oats than for Bromus. Consequently, the roots length and the viability are directly in accordance with the initial hypotheses. With a growing temperature, the germination frequency and the roots length increases, but the viability decreases. With a decreasing water potential (negative), the germination frequency and the roots length decreases, while the viability of ungerminated seeds increases or decreases a little bit for Oats. According to Russell and Blundon (introduction), the results about the temperature and water potential are conclusive. The data about the viability on the temperature and water potential are inversely proportional to data about germination frequency on temperature and water potential. The explanation can be simple. If the germination frequency was high that is because seeds were in favourable conditions. Therefore, seeds that didn't germinate, despite of the fact they were in favourable conditions, should be nonviable and then, necessarily the viability must be low. At a negative water potential, the germination frequency was low, but the viability was high. So, seeds that didn't grow were waiting better conditions to germinate. The used method was adequate, but the quality of Oats seeds was probably very low. That is why the germination frequency for Oats seeds was lower than for Bromus seeds. An interesting improvement of this method could be to buy better seeds, mainly for Oats.




















































































































































































































































































































































































































































































































































































































































































I would like to thank my classmate Jason, who helped me to do this experiment and all students in my class that contributed to the success of this experiment. I would like particularly thank Dr, David J. Blundon for his precious help and for its laboratory manual in which I took a lot of information and ideas.
Blundon, David J. 1994. Ecology: Laboratory Manual. Camosun College, Victoria, Canada.
Hart, J. W. 1988. Light and Plant Growth. Unwin Hyman, London, England.
Krebs, Charles J. 1994. Ecology. HarperCollins College Publishers, New York, USA.
Silvertown, Jonathan W. 1982. Introduction to Plant Population Ecology. Longman Group Limited, New York, USA.