Seed size, germination and seedling growth of Australian species of the desert and halophytic plant

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Seed size, germination and seedling growth of
Australian species of the desert and halophytic
plant genus Frankenia.

• By Lyndlee C. Easton, Molly A. Whalen and Duncan
  A. Mackay

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Seed size and number

• Seed size is an important component in plant life
  histories
• is a measure of amount of resources invested in
  an individual offspring by parent plant.
• Maternal resources for producing seeds are
  limited
• compromise between selection to produce more
  offspring (many small seeds) selection
  favouring greater allocation of maternal
  resources to each offspring (large seeds).

Thus alternate reproductive strategies.
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Advantages of multiple small seeds per fruit.

• Greater number of seeds can be produced
• more chance of some finding suitable site,
• often associated with colonizing species.

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Advantages of a single large seed per fruit.

• Larger seeds produce larger seedlings
• better provisioned.
• Longer roots taller shoots increased access
  to light/soil resources
• competition
• shaded environments
• burial
• survive defoliation
• high risk of drought.

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Drought risk is a significant factor to life
history strategies of arid zone flora. Studies
have suggested that larger seeds in arid zones
impart some kind of advantage. However most
research to date compares these strategies using
seeds from different plant families.
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Frankenia (Frankeniaceae)

• What are frankenias ?
• small shrubs, sub-shrubs, herbs
• halophytes - salt pans, salt lakes, salt marshes
• habit arid desert coastal regions
• specialized soils ie gypsum
• Characteristics.
• white, pink or purple 4- or 5-petalled flowers
• salt glands
• revolute leaves

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Distribution

• Globally -Mediterranean coastal desert regions
  including Europe, the Americas Middle East
• Australia - WA, SA, SW Qld, western NSW, NW Vic,
  southern NT Bass Strait Islands.

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What is the significance of Frankenia in the seed
size/number studies?

• Frankenia include several suites of species that
  vary in seed size number although occurring
  within the same region.
• Overall study is investigating microhabitats to
  search for possible reasons for alternate
  strategies.

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Aims Studies have suggested that large seed size
provides an advantage for seedling establishment
in arid zones. Hypothesis - Large seeds
germinate sooner and at higher percentage of
overall numbers than small seeds.. Seed size
is correlated to seedling size ie. large seeds
produce large seedlings. Compare germination
rates of seeds of various Frankenia species to
test germination success using size as
a predictor of germination rates.
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Aims Arid zones have unpredictable rainfall
events. Frankenia more commonly occur in winter
rainfall zones but rain can occur at any time
-thus temperature may make a difference. Added
the variable of temperature.
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Methods Compared rates of germination of large
seeded species and small seeded species at three
temperatures- 16o, 24o and 30o. Thirteen
species with up to 3 populations per
species. Five large seeded species - size range
gt0.5 mg. Eight small seeded species - size
range lt0.1 mg.
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Methods Grown in germination vials for 30
days. Four replicates of 15 seeds per treatment.
Scored for germination and removed at 2-day
intervals. Germination recorded with emergence
of the radicle
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Results - Did large seeds germinate faster?
Individual species
Large seeds vs. small seeds
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Results Was the overall percentage of
large seeds that germinated by day 30 higher than
small seeds?
Higher germination rates overall at low
temperatures. Small seeded species showed
more variable responses at all three
temperatures. Decline in germination at high
temperature greater in small seeds.
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Results germinated by day 30 per temperature
Note gap in size range.
Small seeds - greater variation between species
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Discussion - Seed germination summary. Larger
seeds tended to germinate more rapidly. Both
large and small seeded species exhibited
higher germination percentages at cooler
temperatures. Decline in germination
percentages at higher temperatures more
pronounced for smaller species. At highest
temperatures, variability in final germination
was greater amongst smaller seeded species.
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Discussion What are the possible advantages of
large seeded species? Grow quickly after a
rainfall event. Prefer cooler conditions
(winter rainfall zone) but can germinate at high
temperatures thus utilise any rainfall event for
germination. Advantageous in an unpredictable
rainfall zone.
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Seedling size and salinity Extent of rainfall
event unknown. If only light or of short
duration, new seedlings will need to cope will
increasing salinity levels as ground water
content decreases. Hypothesis - Large seedlings
have longer roots to keep track with receding
water levels. Do seedlings of small seeded
species cope with higher salinity levels?
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Preliminary salinity trials - Methods Seedlings
germinated and grown for 3 weeks in standardized
conditions. Subjected to 33, 66 and 100
salinity of seawater. Watered every second day
for one month. Dry weights, height, number of
nodes recorded.
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Preliminary results.
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Preliminary results Salinity tolerance.
Number alive at day 30. Ten plants per treatment.
1 plant only
1 plant only
Greater root mass at 33
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Conclusions Do large seeded species germinate
faster and at greater percentages than small
seeded species? Yes - Advantageous to
unpredictable rainfall events. Do seedlings of
small seeded species tolerate higher salinity
levels? Yes Advantageous to smaller seedlings
growing in highly saline areas eg adjacent to
salt pans. Further work Adding more species to
the trials. Include droughting
experiments. Include drought/salinity
experiments.
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Acknowledgments This study is part of PhD
research undertaken at Flinders University,
SA. This project is partially funded
by Australian Flora Foundation Research
Grant Nature Foundation SA Inc. Mark Mitchell
Research Foundation