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Ecosystem Function Nutrients & Nutrient Cycling. Ecosystem function and nutrients Elements that...

Date post:19-Dec-2015
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  • Slide 1
  • Ecosystem Function Nutrients & Nutrient Cycling
  • Slide 2
  • Ecosystem function and nutrients Elements that are required for the growth, maintenance and reproduction of organisms Unlike energy, which eventually leaves the system as heat, nutrients are recycled over and over again Phosphorous (P), carbon (C) and nitrogen (N) are particularly important for life cycling of these three elements is one of the major functions of ecosystems
  • Slide 3
  • Phosphorous Major constituent of nucleic acids, cell membranes, energy transfer systems, bones and teeth Limits plant production in many aquatic habitats Influx of P into rivers and lakes from sewage and agricultural runoff artificially stimulates production in these systems, disrupts ecosystem balance
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  • Phosphorous Phosphorous cycle is chemically uncomplicated, contains fewer steps than other cycles P does not generally undergo oxidation- reduction reactions No significant atmospheric pool most P occurs in mineral deposits and marine sediments
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  • Phosphorous Phosphorous is slowly released to terrestrial and aquatic ecosystems through the weathering of rock Plants assimilate P from soil, often with help from mycorrhizae, and the P is recycled through the ecosystem Unassimilated P is washed into oceans, where it remains in dissolved form until it is finally deposited in ocean sediments
  • Slide 6
  • Phosphorous Cycle
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  • Nitrogen Ultimate source of nitrogen for life is molecular nitrogen (N 2 ) in the atmosphere Atmospheric nitrogen represents largest pool of nitrogen on earth A tiny fraction of this N 2 dissolves into water or is converted by lighting into readily assimilated forms Most nitrogen enters the biological pathways of the nitrogen cycle through fixation by microorganisms
  • Slide 8
  • Nitrogen Although nitrogen fixation / denitrification account for only a small fraction of the earths total nitrogen flux, nearly all the nitrogen that is cycled through biological systems enters the cycle through nitrogen fixation by microorganisms Nitrogen cycle is more complex because nitrogen atoms can take on a greater variety of oxidized and reduced forms
  • Slide 9
  • Nitrogen Cycle Fixation & Assimilation Specialized bacteria reduce atmospheric nitrogen to biologically useful forms with the enzyme nitrogenase (only works under low oxygen concentrations) Fixed nitrogen is available to plants as either ammonium (NH 4 + ) or as nitrate (NO 3 - ) Plants further reduce these compounds into an organic form This organic nitrogen is the most reduced form, with the highest potential chemical energy
  • Slide 10
  • Nitrogen Cycle - Ammonification Organic nitrogen compounds are used by plants (and their consumers) to construct proteins Proteins are eventually metabolized, and excess nitrogen is excreted into the environment as waste this step in the nitrogen cycle is called ammonification (carbon is oxidized in this step, but nitrogen is not)
  • Slide 11
  • Nitrogen Cycle Nitrification & Denitrification The ammonia excreted as waste can be further metabolized by microorganisms in the soil Nitrification is the oxidation of ammonia to nitrite, and then from nitrite to nitrate: NH 3 -> NO 2 - -> NO 3 - Under anaerobic conditions, reduction is thermodynamically favored, and nitrate may be reduced to nitric oxide This process, called denitrification, results in the loss of nitrogen from soils (as a gas): NO 3 - -> NO 2 - -> NO and NO -> N 2 O -> N 2
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  • Nitrogen Cycle
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  • Carbon C is the foundation of all organic molecules Atmospheric C compounds such as carbon dioxide and methane significantly influence global climate Three classes of processes cause carbon to cycle through ecosystems: photosynthesis/respiration exchange of CO 2 between atmosphere and oceans precipitation of carbonate sediments in oceans
  • Slide 14
  • Carbon Cycle Photosynthesis & Respiration about 85 GT of carbon is assimilated by photosynthesis each year approx. 2,650 GT carbon present in total organic matter present in biosphere (in living organisms as well as organic detritus and sediments) average residence time of carbon in organic matter (i.e., time from photosynthetic assimilation to release as CO 2 by respiration) is: 2,650 GT / 85 GT per year = 31 years
  • Slide 15
  • Carbon Cycle Ocean-Atmosphere Exchange CO 2 dissolves readily in water; ocean contains about 50x as much CO 2 as the atmosphere CO 2 continuously exchanged across the ocean/atmosphere boundary total amount in ocean remains constant until new CO 2 enters system from a source outside the atmosphere-ocean system (e.g., burning of fossil fuels) Ocean provides an important sink for excess CO 2 produced by human activities
  • Slide 16
  • Carbon Cycle Precipitation of Carbonates Once it dissolves in water, carbon dioxide forms carbonic acid, which readily dissociates into hydrogen, bicarbonate, and carbonate ions When present, calcium equilibrates with the carbonate ions to form calcium carbonate Calcium carbonate has a low solubility, so it readily precipitates out of the water column to form sediments
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  • Carbon Cycle
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  • Carbon Cycle & Ancient Atmosphere Geologists and paleoecologists can estimate the levels of atmospheric carbon dioxide throughout the earths history burial of organic matter precipitation of carbonates in marine sediments
  • Slide 19
  • Carbon Cycle & Ancient Atmosphere
  • Slide 20
  • Cycle of nutrients through terrestrial ecosystems weathering & atmospheric nutrient input Inorganic soil nutrients plant biomass plant detritus groundwater & stream runoff
  • Slide 21
  • Nutrient Inputs new inorganic nutrients are added to terrestrial ecosystems through: weathering of the bedrock underlying the soil atmosphere - as particulates, ions dissolved in precipitation, or molecular elements (N 2 ) assimilated by bacteria
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  • Slide 23
  • Nutrient regeneration in terrestrial ecosystems Inorganic soil nutrients plant biomass plant detritus mineralization via decomposition mineralization = conversion of organic molecules to inorganic nutrients decomposition usually the slowest (rate limiting) step in nutrient cycling
  • Slide 24
  • Nutrient regeneration in terrestrial ecosystems Inorganic soil nutrients plant biomass plant detritus mineralization via decomposition Uptake of inorganic nutrients by plants and the decomposition of detritus by microorganisms are both biochemical processes influenced by temperature, moisture, and chemical composition of the environment
  • Slide 25
  • Nutrient regeneration in terrestrial ecosystems Chemical characteristics of leaf litter that influence decomposition rate include phosphorous concentration, nitrogen concentration, carbon:nitrogen ratio, and lignin content Increased moisture and temperature also tend to increase the rate of decomposition
  • Slide 26
  • Nutrient regeneration in terrestrial ecosystems decomposition, assimilation rates very high in tropical forests (very little organic matter / nutrients in soil) decomposition very slow in boreal forests dead plant matter builds up on ground and forms thick deposits
  • Slide 27
  • Nutrient cycling in aquatic ecosystems in rivers, lakes & oceans, organic matter sinks to the bottom and accumulates in deep layers of sediment deposits nutrients are regenerated and returned to zones of productivity (near the surface where there is light for photosynthesis) nutrient cycling is generally slower in aquatic systems, because nutrients must travel great distances to reach photic zone for assimilation anaerobic nature of many sediments also slows decomposition and changes the biochemical pathways by which nutrients are regenerated
  • Slide 28
  • Nutrient cycling in aquatic ecosystems mixing of bottom and surface waters is necessary for aquatic ecosystems productivity stratification hinders nutrient cycling in aquatic ecosystems by preventing the mixing of nutrient-rich deep water with surface waters where phytoplankton live
  • Slide 29
  • Slide 30
  • How does ecosystem function respond to natural and human perturbations?
  • Slide 31
  • Effects of disturbance on nutrient cycling disturbance increases nutrient losses from ecosystems
  • Slide 32
  • Effects of disturbance on nutrient cycling nutrient loss post-disturbance is less severe in cold and/or dry climates nutrient loss after disturbance is most rapid in warm, moist conditions that promote rapid decomposition assimilation of nutrients by plants is critical for nutrient retention in these ecosystems luckily, these are also environmental conditions that would promote more rapid plant growth, so effect should be mitigated in nature
  • Slide 33
  • Ecosystem nutrient changes with succession as vegetation develops, soil nitrogen content tends to increase organic carbon content will also increase fraction of phosphorus that is biologically available tends to decrease (assimilated and retained by plants)
  • Slide 34
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