Transcript Stage Four

Stage One: Becoming multicellular
Occurred in water
Enables specialized tissues to develop
Stage Two: Developing sporangia
Enables dispersal on land
Stage Three: Developing a large sporophyte
Confers competitive advantage
Provides perennial spore production
Stage Four: Removing dependence of
fertilization on a film of water
Enables survival in dry environments
Gymnosperms
naked
seed
Stage Four: Removing dependence of fertilization on a film of water
Four major living groups
Cycads (Cycadophyta),
Welwitschia group (Gnetophyta),
Ginkgo, the Maiden Hair Tree (Ginkgophyta),
and the conifers (Pinophyta) .
Cycads and Welwitschia mirabilis
Cycas bougainvilleana
Female cone
Reproduction is by
seeds produced on open
carpophylls or seedbearing leaves.
Microcycas calocoma Photo
Dennis Stevenson
Carbon-14 dating of the largest plants
have shown that some individuals are
over 1500 years old.
Lives in coastal desert regions of Namibia
Female cones
and Angola. Morning fogs provide moisture.
Male cones
Ginko biloba
Illustration in Pen Tsao
Kang Mu of Ginkgo with
seeds (1578)
There are no native ginkgos living in the wild.
The only surviving species of a diverse group
originating in the Permian
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Pangea
Gymnosperms show adaptations
to drier conditions than ferns
both in their reproduction and
vegetative growth
Continental type climates
typically have dry periods or
seasonal rains. These can be
seasonal and may be called
monsoons
In the Permian the land masses
came together and formed a large
continent call Pangea
360 to 286 mya
Carboniferous
Conifer adaptations for harsh environments
Reproductive
1. Airborne male gametophyte (pollen) carried by wind to
the female gametophyte. The fertilized egg is retained and
protected by the sporophyte.
2. Production of a durable seed that at maturity consists
of a protective seed coat, a source of nutrition and an
embryo sporophyte all in one package.
Vegetative
3.
Seed plants have wood producing tissue well developed
for water conduction and support. This enables plants to grow
tall and out-compete neighbors
Xerophyte: a plant that can live where water supply is scanty or
there is physiological drought
Conifer distribution
Life on the edge of the good times!
High
ALPINE
TUNDRA
Elevation
MONTANE
CONIFEROUS
FOREST
DECIDUOUS
FOREST
Low
TROPICAL
FOREST
TROPICAL
FOREST
High
TEMPERATE
DECIDUOUS
FOREST
ARCTIC
NORTHERN TUNDRA
CONIFEROUS
FOREST
Moisture Availability
Low
Fig. 50.11, p. 903
The Pinyon pine-Juniper community
Tap roots stretch down
40 or more feet into the
soil.
Very slow growth rates: a 610 inch diameter tree, 10
feet tall will be 80-100 years
old.
Pinus monophyllum
Zion Canyon
White spruce and the Brooks Range, Alaska
Reproduction in
the conifers
The conifer cone
is a modified
branch.
Usually separate male
and female cones are
borne on the same
plant, i.e., monoecious.
(Not true for Cedrus.)
Each of the numerous scales,
(sporophylls), of the male cone bears
pollen and each female cone scale bears
ovules in which egg cells are produced.
section through one ovule (the red
“cut” in the diagram to the left)
young
female
cone
The conifer life cycle
surface view of one
cone scale (houses
two ovules)
male
cone
section through a
pollen-producing
sac (red cut)
surface view of one
cone scale (houses a
pollen-producing sac )
mature
sporophyte
seed
coat
zygote
embryo
seeding
seed
pollen tube
spermproducing
cell
ovule
Nutritive
material
Haploid Stage
Germination of pollen grain (the male
gametophyte). Sperm nuclei form as
the pollen tube grows toward the egg.
Diploid Stage
fertilization
meiosis
meiosis
Megaspores form,
Microspores form,
develop into pollen grains. one develops into a
female gametophyte.
Wind
pollination
(view inside an ovule)
eggs
female
gametophyte
Fig. 25.16, p. 414
Continuing
vegetative shoot
Pollen grains
Male cone
Pictures of male cone and pollen
Pollen cell nucleus
Generative cell
nucleus
Air sacs
Pine
Microsporangium
Female cone
Female gametophyte
Archegonia
Pictures of female cone
Egg
Only one egg
becomes a
seed
Megagametophyte
Ovule
Single scale (sporophyll
Longitudinal section through ovulate cone
Most conifers are evergreen
Why aren’t all plants evergreen?
What is the advantage of being
deciduous rather than evergreen?
Why is so much of Washington
covered by evergreen conifers?
Foliage retention
Trunk
7
6
5
4
3
2
1 year-old
Current year
Maureen Kennedy
What is the advantage of the deciduous habit
over the evergreen habit?
Deciduous plants are frequently faster growing than
evergreen plants and can rapidly exploit favorable and
reliable habitats.
Leaves do not require to withstand severe cold and leaf
abscission enables nutrients and carbohydrates to be
withdrawn into the plant for re-use
Why is so much of Washington covered by evergreen conifers?
Frequent periods of summer drought but mild wet
winters may favor slower growth outside of summer
rather than dependence on rapid summer growth.
Wind River Canopy
Crane Research Facility
More at: http://faculty.washington.edu/edford/research/research_home.html
Conifer needles
The site of photosynthesis
Exchange between the needle and the
atmosphere of CO2 (into the needle) and
water vapour (out of the needle).
Why is water loss inevitable?
Gaseous exchange takes place through a water film
on the cells inside of the needle and is regulated by
stomata
In Taxus caespitosa and other conifers stomata are arranged in rows
Stomata with guard cells
Leaf cross section of Taxus (yew)
The needle is broad, but still has only one
vascular bundle
The mesophyll is differentiated into palisade and spongy layers
Basics of foliage photosynthesis
Saturation level.
Sometimes called
photosynthetic
capacity
Photosynthetic efficiency:
Increase in photosynthesis
per increase in irradiance
0
0
Any questions?
Compensation point
The irradiance at which CO 2 uptake is zero
Species differences in leaf photosynthesis
A has the highest
photosynthetic rate at light
saturation
B has the highest
photosynthetic efficiency
and the lowest
compensation point.
Units: μmol/m2 /s
micro mols of CO2 per
square meter foliage per
second
Another important measure is called Water Use Efficiency:
the ratio of photosynthesis achieved per unit of water lost.
Units: mmol/mol
milli [m] 0.001 (a thousandth)
milli mols of CO2
micro [µ] 0.000 001 (a millionth)
per mol of water transpired
Old-growth species:
Tsuga heterophylla
Pseudotsuga
menziesii
Notice the
difference in
branch structure
between the species
Thuja plicata
Abies grandis
Upper Canopy
Douglas-fir
Pseudotsuga
Western hemlock
Tsuga
Phot. Cap.
13.1
9.0
Water Use Eff.
μmol/m2/s
Lower Canopy
Phot. Cap. Water Use Eff.
6.2 mmol/mol
8.8
3.5
4.9
3.2
4.8