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Phenotypic plasticity as an indicator for exotic
noxious plants Jing Luo¹, David Tay², John
Cardina¹ ¹Department of Horticulture and Crop
Science, ²Ornamental Plant Germplasm Center, The
Ohio State University, Columbus, Ohio 43210
Introduction Exotic noxious plants, including
invasive plants and exotic weeds, have caused
huge economic loss and ecological damage around
the world. In order to predict the noxious
potential of proposed species and thus prevent
further introductions of possible invasive
species as crops or ornamental plants,
identification of biological and ecological
traits associated with invasiveness and weediness
becomes extremely important. It was suggested
that weeds were usually generalists that can
survive and reproduce in a wide range of
environments, i.e., they were quite plastic in
response to different environments (Baker 1974).
Following this idea, phenotypic plasticity has
been recently proposed as an indicator and
predictor for weeds and invasive plants (Sultan
2001). The objective of this study is to test
the above hypothesis using two exotic dandelion
species Taraxacum officinale (TOF hereafter), a
widespread weed, and T. laevigatum (TLA
hereafter), which is only found in several
locations. Both species were grown in four
different environments. Phenotypic plasticity was
then compared between TOF and TLA.
Results
Conclusions The results indicated that when
grown in different environments, Taraxacum
officinale was more plastic than T. laevigatum in
traits related to morphology, allocation, and
soil property. High phenotypic plasticity may
allows T. officinale to search and capture
resources (such as light and water) more
efficiently when environment changes, and be able
to survive, persist, and reproduce in a wider
range of habitats. This is probably why T.
officinale is a more successful exotic noxious
plant than its close relative, T. laevigatum .
This conclusion could be very useful when
trying to evaluate the potential invasiveness
and weediness of an exotic plant species of high
horticulture value.

• TOF and TLA were significantly different in many
  traits including height, leaf shape index, soil
  pH, and EC. However, there were not many
  significant interactions between species and
  environments except diameter and soil EC. (Table
  1)
• CV (coefficient of variance) was calculated as an
  index of phenotypic plasticity (Fig. 3). TOF
  generally had larger CVs than TLA, and was
  significantly (Plt0.05) more plastic in diameter,
  shootroot ratio, and soil pH (Fig. 4)
• TOF expanded a wider range than TLA for the above
  three traits in different environments. For TOF,
  rosette diameter decreased when shaded, probably
  due to a more upward arrangement of leaves to
  capture light. Rosette diameter increased for
  TLA, accompanied by a less increase in height
  when shaded. Shootroot ratio decreased in a
  larger extend for TOF in dry environment, which
  allowed it to search for more water by investing
  more biomass in root tissue (Fig. 5).
• Soil pH and EC was significantly different for
  the two species, probably due to different root
  exudates. Further study is needed to investigate
  if there is any allelopathic effect related to
  this pH differences.

Fig. 1 Morphology, Ohio distribution, and seed
color of Taraxacum officinale (TOF, weedy), and
T. laevigatum (TLA, non-weedy). TOF and TLA are
both native to Europe. The former usually has
less indented leaves and produces brown-colored
seeds. Leaves are more deeply-indented for the
later one with red-colored seeds. Although very
similar in morphology, TOF is a wide spread
noxious weed found in all Ohio counties, while
TLA has only limited distributions in Ohio.
Future study Another study is being carried out
including a third dandelion species with unknown
weediness potential. Nutrient level is also
included as another environmental factor. This
study will be more concentrated on fitness
components such as reproduction, seed
germination, and seedling establishment.
Fig. 3. This graph shows how CV (coefficient of
variance) was calculated and compared between TOF
and TLA. CV was used as an index of phenotypic
plasticity larger CV means more plastic, and
vice versa. CV was first calculated on 4 plants
grown in different environments for each species
in each replicate, and then compared between
species using type 3 t-test to see if one species
is more plastic than the other.
Fig. 4. Mean CV ( 1 SE) of TOF and TLA for eight
traits. Asterisk indicates significant difference
between two species (Plt0.05, type 3 t-test).
Notice that TOF, the weedy species, had larger
CVs for most traits than TLA, the non-weedy
species.
Literature cited Baker HG. 1974. The evolution of
weeds. Annual Review of Ecology and Systematics
51-24 Sultan SE. 2001. Phenotypic plasticity for
fitness components in Polygonum species of
contrasting ecological breadth. Ecology
82(2)328-43
http//aoki2.si.gunma-u.ac.jp/

• Materials and methods
• TOF and TLA seeds were collected from various
  locations in Columbus and Wooster, OH.
• Seeds were germinated and grown in four
  environments 2 light condition (full light vs.
  green shade)2 soil moisture (wet vs. dry)
• 8 replicates split-plot design with light
  condition as the main plot effect (n222864)
• Plants were maintained in greenhouse from Sep. to
  Dec. 2005, and were then harvested, separated
  into different parts, oven dried and weighted.
• Soil pH and electric conductivity (EC) was
  measured before harvest.

Acknowledgments We thank Emilie Regnier and Maria
Miriti for comments and suggestions, Steven St
Martin and Bert Bishop for statistical advice,
David Snodgrass and Jim Vent for greenhouse care.
Fig. 5. Least square mean (1 SE) of (a) height,
(b) shootroot ratio, and (c) soil pH for both
species in four different environments. CVs of
these three traits were significantly different
between TOF and TLA (see Fig. 4). Notice that TOF
expanded in a wider range than TLA in these three
trait, which indicates TOF is more plastic than
TLA when grown in various environments.
Fig. 2 Green filter (roscolux 4430, Rosco
Laboratories Inc. Stamford, CT) , instead of
neutral shade cloth, was used for shade
treatment. Green filter is better than shade
cloth because it simulates e light competition
environment with other vegetation reduced red
light and increased infraredred ratio.