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Evolutionary history of plants wikipedia , lookup
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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 Ginko biloba- the wonder drug! What, ginkgo? I thought that was just for old people who couldn't keep a train of thought? Nope, you're wrong. Ginkgo can be a very beneficial herb to bodybuilders as well. http://www.teenbodybuilding.com/gingko.htm 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