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6+ProductivityTrophicLevels - Next Wednesday Life in the...

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Next Wednesday: Life in the undergrowth movie - worksheet on D2L - please bring printout to class - material will be on exam
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primary productivity Trophic Levels & Interactions Ecosystems contain diverse assemblages of plants, animals & microorganisms Each species influences flow of energy & nutrients throughout the ecosystem (ecological roles)
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Primary productivity - production of organic compounds from CO 2 - mainly photosynthesis, some chemosynthesis - basis of food webs on the planet 25 % by phytoplankton (< 1% of photosynthetic biomass) 75 % by land plants (90% of total biomass) Primary productivity limited by... Light - Temp. - Water - Nutrients - total biomass accumulated in ecosystem; available to consumers Net = Gross Primary - Respiration Net primary production: - total energy assimilated by producers Gross primary production:
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Primary productivity limited by... Light Compensation point energy gain = energy use via photosynthesis via respiration - below, energy balance is negative - above, energy balance is positive Saturation point rate of photosynthesis stops increasing with light intensity (pigments saturated)
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Primary productivity limited by... Temperature in general, increases with temperature ... but photorespiration ... optimum temp. varies with prevailing temp. in environment Temperate species: 16 C Tropical species: up to 38 C CO 2 uptake - H 2 O loss trade-off Primary productivity limited by... Water productivity increases productivity decreases: waterlogged soil depresses decomposition -> reduces nutrient regeneration
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Mycorrhizae: plant-fungus symbiosis (trade nutrients for sugars); enhance plant’s ability to extract less soluble nutrients, promote nutrient uptake from soil, particularly P Primary productivity limited by... Nutrients (N, P) assigned reading: Whitfield 2007
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Primary productivity limited by... Nutrients (N, P) different spp., different limitations: e.g., experiment with Chaparral species (California) Adenostema shrubs: legume shrub w. root symbionts: annuals (e.g., grasses): control + N + P + N & P control + N + P + N & P control + N + P + N & P respond to N, N+P weak response to P only, bc of N-fixing bacteria strong response to N & to N+P
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