Stage One: Becoming multicellular

1. 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

2. Gymnosperms seed naked 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) .

4. Cycads and Welwitschia mirabilis Cycas bougainvilleana Female cone Microcycas calocoma Photo Dennis Stevenson Reproduction is by seeds produced on open carpophylls or seed-bearing leaves. Carbon-14 dating of the largest plants have shown that some individuals are over 1500 years old. Lives in coastal desert regions of Namibia and Angola. Morning fogs provide moisture. Female cones Male cones

5. 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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7. 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 Carboniferous 360 to 286 mya

8. 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

9. Conifer distribution ALPINE TUNDRA High Elevation DECIDUOUS FOREST Low TROPICAL FOREST ARCTIC TUNDRA TROPICAL FOREST TEMPERATE DECIDUOUS FOREST Moisture Availability High Low Life on the edge of the good times! MONTANE CONIFEROUS FOREST NORTHERN CONIFEROUS FOREST Fig. 50.11, p. 903

10. The Pinyon pine-Juniper community Pinus monophyllum Zion Canyon Tap roots stretch down 40 or more feet into the soil. Very slow growth rates: a 6-10 inch diameter tree, 10 feet tall will be 80-100 years old.

11. White spruce and the Brooks Range, Alaska

12. The conifer cone is a modified branch. Reproduction in the conifers 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. http://forest.wisc.edu/forestry415/INDEXFRAMES.HTM

13. The conifer life cycle section through one ovule (the red “cut” in the diagram to the left) young female cone ovule male cone seed coat embryo Nutritive material meiosis meiosis pollen tube sperm-producing cell eggs female gametophyte surface view of one cone scale (houses two ovules) section through a pollen-producing sac (red cut) surface view of one cone scale (houses a pollen-producing sac ) mature sporophyte zygote seeding Diploid Stage seed fertilization Haploid Stage Megaspores form, one develops into a female gametophyte. Microspores form, develop into pollen grains. (view inside an ovule) Wind pollination Germination of pollen grain (the male gametophyte). Sperm nuclei form as the pollen tube grows toward the egg. Fig. 25.16, p. 414

14. Pictures of male cone and pollen Continuing vegetative shoot Male cone Pollen cell nucleus Generative cell nucleus Air sacs Microsporangium Pollen grains Pine

15. Pictures of female cone Female gametophyte Female cone Archegonia Egg Ovule Single scale (sporophyll Only one egg becomes a seed Megagametophyte Longitudinal section through ovulate cone

16. 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?

17. Foliage retention Trunk 7 6 5 4 3 2 1 year-old Current year Maureen Kennedy

18. 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.

19. Wind River Canopy Crane Research Facility More at: http://faculty.washington.edu/edford/research/research_home.html

20. 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

21. Stomata with guard cells In Taxus caespitosa and other conifers stomata are arranged in rows

22. Leaf cross section of Taxus (yew) The needle is broad, but still has only one vascular bundle The mesophyll is differentiated into palisadeand spongylayers

23. Basics of foliage photosynthesis Saturation level. Sometimes called photosynthetic capacity Photosynthetic efficiency: Increase in photosynthesis per increase in irradiance 0 0 Compensation point The irradiance at which CO uptake is zero 2 Any questions?

24. Species differences in leaf photosynthesis 2 Units: μmol/m /s micro mols of CO per square meter foliage per second 2 Units: mmol/mol milli mols of CO per mol of water transpired 2 A has the highest photosynthetic rate at light saturation B has the highest photosynthetic efficiency and the lowest compensation point. Another important measure is called Water Use Efficiency: the ratio of photosynthesis achieved per unit of water lost. milli [m] 0.001 (a thousandth) micro [µ] 0.000 001 (a millionth)

25. Old-growth species: Upper Canopy Lower Canopy Phot. Cap. Water Use Eff. Phot. Cap. Water Use Eff. Douglas-fir Pseudotsuga 2 13.1 6.2 8.8 3.5 mmol/mol μmol/m /s Western hemlock Tsuga 9.0 4.9 3.2 4.8 Tsuga heterophylla Pseudotsuga menziesii Thuja plicata Abies grandis Notice the difference in branch structure between the species