Week 6/2/09 9; Wednesday Announcements Family ID final in lab today Key final in lab next Wednesday (practice keying on Monday) Lecture: Parasitic Plants All organisms can be categorized into two groups on the basis of how they obtain their carbon-based basic sugars for building complex cell structures: Autotrophs (self-nourish) produce their own food Heterotrophs (other-nourish) obtain food from other organisms, alive or dead Photosynthesis - characterizes plants from unicellular green algae to the largest trees. This process enables the plant to construct the basic building blocks for growth sugars and complex carbohydrates (including cellulose) - from energy obtained from the sun. Chemically it looks something like this: H2O + CO2 + E(sun) --> (CH2O)n +O2 Photosynthetic eukaryotes (plants and algae) are derived from the Endosymbiosis of a cyanobacterium and a non-photosynthetic eukaryotic cell at some point a long time ago. Plants have many adaptations to enable them to be efficient factories for the production of carbohydrates from sunlight - broad, thin leaf blades with the thickness and pigmentation optimal for capturing sunlight - stems, branches, and petioles enabling the organization of leaves on a plant to be positioned to overlap minimally and capture as much of the light that arrives in the area of the plant as possible. Some leaves even track the sun's movement. - Roots that can grow in any direction to find water - even to a depth of 70 feet! Some plants have evolved to be heterotrophic - either partially or completely. These are called parasites. Parasite - an organism that grows, feeds, and is sheltered on, or in, a different organism at the expense of that organism and contributing nothing to the survival of its host. This is one type of symbiosis. The others are: mutualism - both organisms benefit commensalism - one organism benefits, while the other neither benefits or suffers Page 67
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Becoming a parasite. The parasite connects to the host plant by means of a haustorium. This is a suckerlike swelling on a root or stem, which invades a host root or stem and makes a connection between the vascular tissue of the parasite and host. In the case of parasites on fungi, the parasite induces the fungus to grow into the root of the plant and then turns the table and sucks the nutrients from the fungus. Plants that obtain all of their nutrients from the host are called holoparasites (or obligate parasites). However some parasites remain capable of photosynthesis, while supplementing their diet with the host plant nutrients. These plants are called hemiparasites (or facultative parasites). Parasitic Reduction Syndrome (holoparasites): This combination of traits is repeated in many different groups of parasitic plants. The dramatic difference relative to other related plants that are not photosynthetic often results in segregating them into distinct families (eg, Orobanchaceae from Scrophulariaceae; Monotropaceae from Ericaceae; Lennoaceae from Boraginaceae; Cuscutaceae from Convolvulaceae) 1) Loss of leaves - leaves reduced to scales 2) Small overall size of plant - no need for large plants to hold leaves 3) Loss of roots - reduced to short, stumpy projections with haustoria 4) Loss of chlorophyll 5) Loss of genes needed for photosynthesis overhead of Epifagus cp genome 6) Higher substitution rate (more rapid DNA divergence) in genes that are not lost overhead of Cuscuta in Convolvulaceae phylogeny Use it or lose it!! A maxim in evolution. Not all parasites are small. There are many shrubs and trees among them (though not as holoparasites), including the Australian Christmas tree, Nuytsia floribunda (Loranthaceae). However, the flower still is necessary for reproduction and usually is similar enough to the non-parasitic ancestors to indicate relationships. Often the only structures left on the plant are those needed to produce the flower and expose it to the insects or other agent needed for pollination.
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6/2/09 Parasitism has evolved perhaps 20 times among flowering plants. In each case the plants have become parasitic on either other plants or fungi. These include 4 families we know: Boraginaceae, Scrophulariaceae, Ericaceae, Orchidaceae (overhead - Chase et al. tree; black - plant parasites; green - fungal parasites or mycotrophs) In Scrophulariaceae/Orobanchaceae parasitism evolved only once, but loss of photosynthesis evolved several times (overheads) In some cases (eg, Orchidaceae), parasitism probably has evolved many times fairly recently in one family. There are quite a few families of parasitic plants that probably are quite ancient (Hydnoraceae, Cynomoraceae, Balonophoraceae); Rafflesiaceae once was thought to be ancient, but we now know it is nested within Euphorbiaceae. They have evolved both very tiny flowers (only a few cells in the case of some Balanophoraceae), but also include the largest flower in the world (Rafflesia - 3 feet or more in diameter!) overhead. In some cases, the closest relatives are of these plants are unknown; perhaps they went extinct long ago. Their positions in the tree are difficult to determine, because either they have no close relatives, or their morphology is unique and doesn't provide a clue to relationships and their DNA sequences have diverged rapidly. In the case of Rafflesia the entire plant consists of thread-like root cells that grow in among the cells of the host plant and the only way one knows the plant exists is when the flower emerges - the ultimate Parasitic Reduction Syndrome.
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6/2/09 Week 9; Friday Guest Lecture: Sarah Reichard, UW Botanic Gardens, Center for Urban Horticulture Alien Invasive plants in the Pacific Northwest. "Native Plant" Definition must include reference to time and place. Most people consider `native' to mean pre-European settlement, so we can refer to plants that are native to Washington, the Pacific Northwest, or North America, meaning those plants found in these regions prior to settlement by Europeans. Invasive, non-native species are those that can or have spread into native wilderness or managed ecosystems, develop self-sustaining populations, and become dominant or disruptive to those systems. Potential for new weed species (estimate by Rappaport 1991) With ca. 260,000 species of flowering plants and about 10% of those as good colonizers, that makes about 26,000 potential weeds. There are now about 10,000 species recognized as weeds and, of them, about 4,000 have spread to other continents. So even with a conservative estimate of 10% of the remaining species becoming successful weeds, that leaves more than 2,000 more potential weeds. Why the concern with European settlement as a starting point? Natural seed dispersal is a very slow phenomenon Europeans exploration and colonization represented the beginning of frequent and wide travel by people from one part of the planet to all other parts. They purposefully carried many plants with them and accidentally carried many more. Example Hawaii Native plant colonization rate: 1 species per 100,000 years After Polynesian settlement: 1/50,000 years After European settlement: 4/year (now more like 5/year) 1000 species have arrived in the last 200 years of a total of 5000 estimated colonization events in the entire history geologic of the islands.
How do Invasive plants drive out other species? By competition for resources. 1. Light eg, Kudzu (Pueraria lobata) and English Ivy (Hedera helix) grow over other plants and cut off their light source Page 70
6/2/09 2. Water Many invasive plants can make better use of water in the soil, thus leaving too little for native plants 3. Attract pollinators or dispersers away from native species so that the natives do not reproduces as effectively. For example, purple loosestrife (Lythrum salicaria) outcompetes native plants for bees as pollinators, thus reducing reproduction by natives. Allelopathy producing secondary chemical compounds that inhibit, or `poison' other plants. Geranium robertianum (Herb Robert or Stinky Bob) is an example. By engineering communities 1. Adding nitrogen to soils - increases rate of succession - permits more alien species to colonize - makes natives that are adapted to the nutrient poor soils uncompetitive Example: Morella faya in Hawaii growing on sterile lava flows Example: Scot's broom (Cytisus scoparius) in the Puget Sound Prairies, where this legume with nitrogen-fixing bacteria in its root nodules, increases the N content of the soils, permitting more aliens to colonize and increasing the rate of succession to forest Counter example: Knotweed (Polygonum spp.) has the reverse effect in riparian areas here in Western Washington. It translocates N from leaves to rhizomes at the end of the growing season and then moves it back into new leaves in the spring. Native plants (alders and willows) deposit lots of N into the streams and streamside ecosystems in the leaves each year contributing to the nutrients available for invertebrates and, indirectly, to trout and other salmon. 2. Sending down deep roots and lowering the water table so native plants can't get sufficient water. Tamarisk (Tamarix ramocissima) is particularly bad for this along rivers in the desert SW, but also now known in eastern Washington. Tamarisk also traps sediments and organic material thus stabilizing banks and channelizing rivers, thus destroying flood plain habitats. 3. Stabilizing habitats in areas that are naturally disturbed - beach and salt-marsh grasses, such as Spartina alterniflora, can stabilize mud flats and catch sediments, thus converting shallow estuaries into stable land (almost like filling a wetland). Example: Willapa Bay in SW Washington 4. Increasing the frequency and intensity of fires - by increasing fuel load (some grasses that die each year) or by being a fastburning plant (gorse Ulex europaeus), fires can become more common or more intense, thus altering the native plant community. Pennisetum setaceum is a grass that invades dry forests in Hawaii and helps spread fires in habitats where fires were rare before.
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6/2/09 5. Vines adding weight to tree canopies. English Ivy has thick, evergreen leaves, which adds a lot of weight to deciduous tree canopies in the winter when they don't usually have the weight of leaves and causes trees to fall in wind storms. Some invasive plants can be harmful or even deadly. For example, Giant Hogweed Heracleum mantegazzianum can cause harmful burns on the skin from the sap in the stems and leaves. This is a class "A" noxious weed, which means that all means of eradicating it should be taken (this designation is generally used only for weeds that are still limited enough that eradication is feasible). Hybridization with non-native plants also can dilute gene pools and in some cases even extirpate native species (eg, rainbow trout hybridizing with and eliminating cutthroat trout from throughout most of the native range of cutthroat trout).
Causes of endangerment of imperiled species in the US: Habitat destruction 88% Non-native species 46% Pollution 20% Overharvest 14% Disease 2% Positive impacts of Invasive plants (these usually are outweighed by their negative impacts) Food or shelter for animals Erosion control many species planted during `dust bowl' in 1930's have become invasive Aesthetically pleasing many were first introduced for ornamental purposes Some species can produce useful goods for people (fruit, wood, etc.) Useful for pollination or other ecological services the Honey bee is an introduced species. How do alien introductions occur? Landscape plants 82% of all woody invasive plants (ca. 2/3...