The Effects of Proximity to Unrelated and Kin Plants on Determining Wheatgrass
(Triticum aestivum) Root Growth
Ashley Huffman, Andrew Dyjak, and Karl Jackson
Department of Biological Science
Saddleback College
Mission Viejo, CA 92692
28 April 2014
Plant growth, especially root development, can be effected by the type and
proximity of plants neighboring it. A proposed question arose regarding distance to kin
plants and whether this would inhibit or promote root development. It was predicted that
wheatgrass plants grown near unrelated plants of the same species would produce larger
roots than those grown next to kin plants. Liquid Sunshine wheatgrass seeds were planted
into three different groups (with kin Liquid Sunshine wheatgrass seeds, with unrelated
Common wheatgrass seeds and with unrelated Red Hard wheatgrass seeds) and the roots
were then measured after twenty days. The mean length of the Liquid Sunshine wheatgrass
plant roots grown in the first tray, or kin group, was 10.83cm (N = 10). The mean length of
the Liquid Sunshine wheatgrass plant roots grown in the second tray, with the Common
wheatgrass plants, was 13.41cm (N = 10). The mean length of the Liquid Sunshine
wheatgrass plant roots grown in the third tray, with the Red Hard wheatgrass plants, was
12.79cm (N = 10). Wheatgrass plants grown within close proximity to unrelated plants of
the same species do not produce larger roots when compared to those grown next to kin
plants (p = 0.172026, one-tailed ANOVA).
Introduction
There has been a prevalent association
between root development and plant relatedness
observed by many scientific studies, yet the extent of
this relationship and its impact on agriculture is still
highly debated. Based on the research by Biedrzycki &
Bais, (2011) it was found that plants can, in fact,
recognize other plants in their surroundings based on
relatedness. Biedrzycki & Bais, (2010) noted that
plant–plant interactions have been well documented
and range from negative interactions, such as
allelopathy, to positive interactions such as the release
of volatile compounds as a warning to other plants.
Fang et al., (2013) found that belowground tissues,
such as roots, can not only detect, but also respond to
changes in their environment; exhibiting adaptation in
their morphology and physiology in response to
environmental stimuli, such as alteration in total root
length, root system volume, and root depth.
Further analysis by Milla et al., (2009) found
that certain plants can identify their kin in competitive
settings through root recognition, and can, in turn, react
by decreasing their root growth when competing with
relatives. A specific example of this was illustrated by
Dudley & File (2007) which reported that an annual
plant exhibited kin recognition, as the plant produced
more roots when grown in pots with strangers (plants
of the same species, but grown from seeds collected
from different mother plants) versus being grown with
kin plants (plants grown from seeds collected from the
same mother plant).
In another related study, Murphy & Dudley
(2009), it too produced similar results in which they
analyzed data that indicated plants exhibited both
increased competition toward stranger plants and
reduced interference (cooperation) toward kin plants.
The broader impacts of this topic have also been
investigated in the study by Milla et al., (2009) which
asserted the generalization that kin recognition may act
as a widespread, major microevolutionary mechanism
in plants to reduce competition among related plants
and create competition between unrelated plants. Our
current study addresses many of these issues and will
focus primarily on the question of whether wheatgrass
plants grown within close proximity to unrelated plants
of the same species will produce larger roots as
opposed to those grown next to kin plants.
Materials and Methods
The experiment was performed at the Biology
Greenhouse at Saddleback College in Mission Viejo,
California from 2-21 April 2014. There were four sets
Tray 1
Tray 2
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LS x LS
LS x CW
Tray 3
LS x RHW
Figure 1. Diagram of planting arrangement. LS =
Liquid Sunshine Wheatgrass; CW = Common
Wheatgrass; RHW = Red Hard Wheatgrass (Note:
Diagram not to scale).
The planting method used was obtained from
the organic seed packets (Botanical Interests & Handy
Pantry Seed Co.) and all trays were filled with Foxfarm
Natural & Organic Ocean Forest Potting Soil and
respectively labeled. Using Figure One, all seeds were
planted with 1/4 inch (0.635cm) spacing between each
seed and planted 1/8 inch (0.318cm) deep. The seeds
were then carefully covered with soil and watered with
de-ionized water. All trays/groups were watered three
times a week with de-ionized water and were originally
planted towards the middle of the greenhouse, but once
sprouting occurred (on day 8) were relocated to a
window location in the greenhouse. After the growth
period of twenty days passed, the roots were cut,
washed, dried, measured and then weighed and
compared to determine the outcome of the hypothesis.
On 21 April 2014, all Liquid Sunshine
wheatgrass plant roots were cut, washed using deionized water to ensure no soil remained in the roots
and then blotted dry with a paper towel. Each of the
plant’s longest roots were measured using a metric
ruler to the nearest 0.1cm and recorded into the lab
notebook. Due to the roots being extremely small, thin,
and intertwined with the other roots, it was difficult to
measure each root on the plant, so the longest root was
measured and recorded. In addition, the roots were
very small and a more precise scale was needed to
individually weigh each root. Therefore, the total
weight for the roots of all 10 plants in each group was
found to the nearest 0.01g with an analytic balance
(Scout Pro) in a 150ml. All data were transferred to MS
Excel (Microsoft Corporation, Redmond, Washington)
where all further statistical manipulations were
performed.
Results
The mean length of the Liquid Sunshine
wheatgrass plant roots grown in the first tray, or kin
group, was 10.83cm (N = 10). The mean length of the
Liquid Sunshine wheatgrass plant roots grown in the
second tray, with the Common wheatgrass plants, was
13.41cm (N = 10). The mean length of the Liquid
Sunshine wheatgrass plant roots grown in the third
tray, with the Red Hard wheatgrass, was 12.79cm (N =
10). After 20 days of germination, it was found that
there was no statistical difference between the mean
root lengths of all three groups (p = 0.172026, onetailed ANOVA). These data are shown in Figure Two.
ROOT LENGTH (CM)
of 10 Liquid Sunshine wheatgrass plants (Triticum
aestivum) used in this study (N = 10). Prior to planting,
these 40 Liquid Sunshine wheatgrass seeds were
harvested from one mature organic Liquid Sunshine
wheatgrass plant. All of the wheatgrass seeds were
planted on 2 April 2014 following the same planting
procedure. Three large plastic planting trays (20.32cm
x 20.32cm) were used with twenty wheatgrass seeds
per tray, arranged in the following order; the first tray
was the kin group and had twenty organic Liquid
Sunshine wheatgrass seeds from the same plant, the
second tray had ten organic Liquid Sunshine
wheatgrass seeds and ten organic Common wheatgrass
seeds with alternating planting, and the third group had
ten organic Liquid Sunshine wheatgrass seeds and ten
organic Hard Red wheatgrass seeds again with
alternating planting. The setup and arrangement of the
planting is shown in Figure One.
16
14
12
10
8
6
4
2
0
1
2
3
GROUP/TRAY
Figure 2. Comparison of mean root length for Liquid
Sunshine wheatgrass plants grown next to kin plants
and next to unrelated plants of the same species (N =
10). The mean root length of wheatgrass plants grown
next to unrelated plants of the same species is not
larger than the mean root length of wheatgrass plants
grown next to kin plants (p =0.172026, single factor
ANOVA).
The total weight for all of the Liquid Sunshine
wheatgrass plant roots in each tray was also collected
and found to be 0.14g for tray 1, 0.27g for tray 2, and
0.32g for tray 3. Since only total weight was recorded,
statistical analysis could not be run for these data but a
TOTAL WEIGHT (G)
graph has been included to show weight difference
among the roots in Figure Three.
0.35
0.3
0.25
0.2
0.15
0.1
0.05
0
1
2
3
GROUP/TRAY
Figure 3. Comparison of total weight for Liquid
Sunshine wheatgrass plant roots grown next to kin
plants and next to unrelated plants of the same species
(N = 10).
Discussion
In this study, the results did not support the
proposed hypothesis. The Liquid Sunshine wheatgrass
plants grown within close proximity to unrelated plants
of the same species did not produce larger roots when
compared to Liquid Sunshine wheatgrass plants grown
next to kin plants. Although the data collected yielded
larger numbers in groups 2 and 3 for both mean root
length and overall root weight when compared to group
1, statistically this was not a large enough difference to
show the hypothesis to be correct. The overall trend of
the kin group having the shortest mean root length and
lowest total root weight was clearly evident, however,
this difference in size was not great enough to
definitively conclude that proximity to kin plants
effects root size. There are several factors that may
have contributed to why these results were obtained.
Despite efforts to ensure a consistent
environment by growing all the wheatgrass plants in
the same greenhouse and placing them in the same
location within the greenhouse, certain conditions
observed contradict the belief that this environment
was uniform for all trays. For example, although all of
the groups were watered the same amount and at the
same times, the consistency of how ‘wet’ the soil was
would fluctuate. The air circulation within the
greenhouse may have caused the soil in certain trays to
become dryer and inhibited root growth. In addition,
the trays seems to be growing at different rates, with
tray 2 seeming to grow the slowest. An uneven
distribution of direct sunlight, as well as proximity to
air ventilation, may have contributed to why tray 2
seemed to be growing at a slower rate than the other
trays.
Although we can conclude that the
environmental conditions within the greenhouse may
not have been optimal for ideal plant growth, there are
other factors which may have effected the results as
well. Despite pH of the soil not having been measured,
it could have been a variable which affected the
outcome of this study. More significantly, however, the
type of plant used in this experiment is not one that any
of the previous research has been based upon. In
addition, the research gathered for this study used
different methods of growing and measuring the plants
and their roots. As in Dudley & File (2007) which
reported that an annual plant exhibited kin recognition,
as the plant produced more roots when grown in pots
with strangers versus being grown with kin plants. The
use of large plastic trays instead of individual pots, as
well as the need for a different species of plant, could
have negatively impacted the wheatgrass plant’s root
growth. This is especially true when taking into
account how intertwined and thin the roots of the
wheatgrass plants were and furthermore supports the
necessity of a different species of plant, perhaps an
annual or bean plant, whose roots are much more
defined.
Further studies are needed to distinctly define
the effects of proximity to unrelated and kin plants on
determining root growth. Suggestions for such future
endeavors include using different plants to study whose
roots are much more well-defined in addition to using
different methods of evaluating them, such as
measuring distance of roots from other plants and/or
individually weighing and measuring each root. The
findings produced from these future experiments could
yield results that would impact agricultural practices
currently in place in order to accommodate the need for
plants in geographical areas that will not outcompete
each other for nutrients.
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