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Home , Chemical cycling, Chemosynthesis

Overview: Cool Chapter 55 • An ecosystem consists of all the living in a , as well as the abiotic factors with and Restoration which they interact • Ecosystems range from a microcosm, such as an aquarium, to a large area such as a lake or forest • Ecosystems’ dynamics involve two main processes: and chemical cycling • Energy flows through ecosystems while matter cycles within them

Concept 55.1: Physical laws govern energy Conservation of Energy flow and chemical cycling in ecosystems • Laws of physics and chemistry apply to • Ecologists study the transformations of energy ecosystems, particularly energy flow and matter within their system • The first law of thermodynamics states that energy cannot be created or destroyed, only transformed • Energy enters an ecosystem as solar radiation, is conserved, and is lost from organisms as heat

Conservation of Mass

• The second law of thermodynamics states that • The law of conservation of mass states that every exchange of energy increases the entropy of matter cannot be created or destroyed the universe • Chemical elements are continually recycled within • In an ecosystem, energy conversions are not ecosystems completely efficient, and some energy is always • In a forest ecosystem, most nutrients enter as dust lost as heat or solutes in rain and are carried away in water • Ecosystems are open systems, absorbing energy and mass and releasing heat and waste products Energy, Mass, and Trophic Levels

• build molecules themselves using • Energy and nutrients pass from primary or chemosynthesis as an energy producers (autotrophs) to primary consumers source () to secondary consumers • depend on the biosynthetic output of () to tertiary consumers (carnivores other organisms that feed on other carnivores)

Figure 55.4

Sun Key Chemical cycling • , or , are consumers Heat Energy flow that derive their energy from , nonliving Primary producers organic matter • Prokaryotes and fungi are important detritivores Primary Detritus • connects all trophic levels consumers

Secondary and and other tertiary consumers detritivores

Concept 55.2: Energy and other limiting Ecosystem Energy Budgets factors control in • The extent of photosynthetic production sets the ecosystems spending limit for an ecosystem’s energy budget • In most ecosystems, primary production is the amount of light energy converted to chemical energy by autotrophs during a given time period • In a few ecosystems, chemoautotrophs are the primary producers The Global Energy Budget Gross and Net Production

• The amount of solar radiation reaching the Earth’s • Total primary production is known as the surface limits photosynthetic output of ecosystems ecosystem’s gross primary production (GPP) • Only a small fraction of solar energy actually • GPP is measured as the conversion of chemical strikes photosynthetic organisms, and even less is energy from photosynthesis per unit time of a usable wavelength • Net primary production (NPP) is GPP minus energy used by primary producers for respiration • NPP is expressed as − Energy per unit area per unit time (J/m 2⋅yr), or − added per unit area per unit time (g/m 2⋅yr)

Figure 55.5 TECHNIQUE

80 Snow

• NPP is the amount of new biomass added in a Clouds given time period 60 • Only NPP is available to consumers Vegetation • Standing crop is the total biomass of 40 photosynthetic autotrophs at a given time Soil Percentreflectance • Ecosystems vary greatly in NPP and contribution 20 to the total NPP on Earth Liquid water 0 400 600 800 1,000 1,200

Visible Near-infrared Wavelength (nm)

Figure 55.6

Net primary production • Tropical rain forests, estuaries, and coral reefs are (kg carbon/m 2....yr)

among the most productive ecosystems per unit 3 area • Marine ecosystems are relatively unproductive per 2 unit area, but contribute much to global net primary production because of their volume 1

0 Figure 55.7

• Net ecosystem production (NEP) is a measure Float surfaces of the total biomass accumulation during a given for 6–12 hours period to transmit data to satellite. • NEP is gross primary production minus the total respiration of all organisms (producers and Total cycle time: Float descends 10 days consumers) in an ecosystem to 1,000 m and “parks.” O2 concentration is • NEP is estimated by comparing the net flux of CO 2 recorded as float ascends. and O 2 in an ecosystem, two molecules connected by photosynthesis Drift time: 9 days

• The release of O 2 by a system is an indication that it is also storing CO 2

Primary Production in Aquatic Ecosystems Light Limitation

• In marine and freshwater ecosystems, both light • Depth of light penetration affects primary and nutrients control primary production production in the photic zone of an or lake

Figure 55.8 RESULTS Nutrient Limitation 30 Ammonium enriched • More than light, nutrients limit primary production 24 Phosphate in geographic regions of the ocean and in lakes enriched • A limiting nutrient is the element that must be Unenriched added for production to increase in an area 18 control • Nitrogen and phosphorous are typically the nutrients that most often limit marine production 12 • Nutrient enrichment experiments confirmed that density nitrogen was limiting phytoplankton growth off (millionsofcells per mL) 6 the shore of Long Island, New York 0 ABCGD E F Collection site • Experiments in the Sargasso Sea in the subtropical Atlantic Ocean showed that iron limited primary production • Upwelling of nutrient-rich waters in parts of the contributes to regions of high primary production • The addition of large amounts of nutrients to lakes has a wide range of ecological impacts

Primary Production in Terrestrial Ecosystems • In some areas, sewage runoff has caused eutrophication of lakes, which can lead to loss of • In terrestrial ecosystems, temperature and most fish species moisture affect primary production on a large • In lakes, phosphorus limits cyanobacterial growth scale more often than nitrogen • Primary production increases with moisture • This has led to the use of phosphate-free detergents

Nutrient Limitations and Adaptations That Reduce Them • Actual evapotranspiration is the water transpired by plants and evaporated from a landscape • On a more local scale, a soil nutrient is often the • It is affected by precipitation, temperature, and limiting factor in primary production solar energy • In terrestrial ecosystems, nitrogen is the most • It is related to net primary production common limiting nutrient • Phosphorus can also be a limiting nutrient, especially in older soils Concept 55.3: Energy transfer between trophic levels is typically only 10% efficient • Various adaptations help plants access limiting nutrients from soil • Secondary production of an ecosystem is the – Some plants form mutualisms with nitrogen-fixing amount of chemical energy in food converted to bacteria new biomass during a given period of time – Many plants form mutualisms with mycorrhizal fungi; these fungi supply plants with phosphorus and other limiting elements – Roots have root hairs to increase surface area – Many plants release enzymes that increase the availability of limiting nutrients

Figure 55.10 Production Efficiency

• When a caterpillar feeds on a leaf, only about one-sixth of the leaf’s energy is used for Plant material secondary production eaten by caterpillar • An ’s production efficiency is the 200 J fraction of energy stored in food that is not used for respiration Production Net secondary production × 100% 67 J Cellular = 100 J respiration efficiency Assimilation of primary production Feces 33 J

Not assimilated Growth (new biomass; Assimilated secondary production)

Trophic Efficiency and Ecological Pyramids

• Birds and mammals have efficiencies in the • Trophic efficiency is the percentage of range of 1 −3% because of the high cost of production transferred from one to the endothermy next • Fishes have production efficiencies of around • It is usually about 10%, with a range of 5% to 20% 10% • Trophic efficiency is multiplied over the length of a • Insects and microorganisms have efficiencies of 40% or more • Approximately 0.1% of chemical energy fixed by photosynthesis reaches a tertiary • A pyramid of net production represents the loss of • In a biomass pyramid, each tier represents the dry energy with each transfer in a food chain weight of all organisms in one trophic level • Most biomass pyramids show a sharp decrease at successively higher trophic levels

Figure 55.12 Trophic level Dry mass (g/m 2)

Tertiary consumers 1.5 Secondary consumers 11 • Certain aquatic ecosystems have inverted Primary consumers 37 Primary producers 809 biomass pyramids: producers (phytoplankton) are consumed so quickly that they are outweighed by (a) Most ecosystems (data from a Florida bog) primary consumers • Turnover time is a ratio of the standing crop biomass to production

Trophic level Dry mass (g/m 2)

Primary consumers (zooplankton) 21 Primary producers (phytoplankton) 4

(b) Some aquatic ecosystems (data from the English Channel)

Concept 55.4: Biological and geochemical processes cycle nutrients and water in • Dynamics of energy flow in ecosystems have important implications for the human population ecosystems • Eating meat is a relatively inefficient way of • Life depends on recycling chemical elements tapping photosynthetic production • Nutrient circuits in ecosystems involve biotic and • Worldwide agriculture could feed many more abiotic components and are often called people if humans ate only plant material biogeochemical cycles Biogeochemical Cycles

• Gaseous carbon, , , and nitrogen • A model of nutrient cycling includes main occur in the atmosphere and cycle globally reservoirs of elements and processes that transfer • Less mobile elements include phosphorus, elements between reservoirs potassium, and calcium • All elements cycle between organic and inorganic • These elements cycle locally in terrestrial systems, reservoirs but more broadly when dissolved in aquatic systems

Figure 55.13 Reservoir A Reservoir B Organic materials Organic available as materials nutrients unavailable as nutrients Fossilization Living Peat • In studying cycling of water, carbon, nitrogen, and organisms, Coal detritus phosphorus, ecologists focus on four factors

Oil Respiration, – Each chemical’s biological importance decomposition, excretion Burning of – Forms in which each chemical is available or used fossil fuels by organisms Assimilation, photosynthesis – Major reservoirs for each chemical Reservoir D Reservoir C Inorganic materials Inorganic materials – Key processes driving movement of each unavailable available as as nutrients nutrients chemical through its cycle , Atmosphere erosion Minerals Water in rocks Formation of Soil sedimentary rock

Figure 55.14a

The

• Water is essential to all organisms Movement over • Liquid water is the primary physical phase in which land by wind Evaporation Precipitation water is used Precipitation from ocean over land over ocean • The oceans contain 97% of the ’s water; Evapotranspira- 2% is in glaciers and polar ice caps, and 1% is in tion from land lakes, rivers, and groundwater Percolation • Water moves by the processes of evaporation, through soil transpiration, condensation, precipitation, and Runoff and groundwater movement through surface and groundwater The • CO 2 is taken up and released through • Carbon-based organic molecules are essential to photosynthesis and respiration; additionally, all organisms volcanoes and the burning of fossil fuels contribute CO 2 to the atmosphere • Photosynthetic organisms convert CO 2 to organic molecules that are used by heterotrophs • Carbon reservoirs include fossil fuels, soils and sediments, solutes in oceans, plant and biomass, the atmosphere, and sedimentary rocks

Figure 55.14b

CO 2 in atmosphere Photosynthesis The Photo- Cellular synthesis respiration • Nitrogen is a component of amino acids, , and nucleic acids Burning of fossil • The main reservoir of nitrogen is the atmosphere fuels and (N ), though this nitrogen must be converted to wood Phyto- 2 + – NH 4 or NO 3 for uptake by plants, via nitrogen Consumers fixation by bacteria Consumers

Decomposition

Figure 55.14c

N2 in atmosphere

Reactive N + gases • Organic nitrogen is decomposed to NH 4 by Industrial + – fixation ammonification, and NH 4 is decomposed to NO 3 by N fertilizers – Fixation • Denitrification converts NO 3 back to N 2

Dissolved Runoff – NO 3 Terrestrial organic N N2 cycling + NO – NH 4 3 Aquatic cycling Denitri- fication Decomposition and Decom- Assimilation position NO – Fixation Uptake 3 in root nodules of amino acids Ammonification Nitrification

+ – NH 3 NH 4 NO 2 Figure 55.14d

Wind-blown The dust

• Phosphorus is a major constituent of nucleic Geologic Weathering acids, phospholipids, and ATP uplift of rocks Runoff 3– • Phosphate (PO ) is the most important Consumption 4 Decomposition inorganic form of phosphorus Plant Plankton Dissolved uptake PO 3– of PO 3– • The largest reservoirs are sedimentary rocks of 4 4 Uptake Leaching marine origin, the oceans, and organisms Sedimentation • Phosphate binds with soil particles, and movement is often localized Decomposition

Figure 55.15 EXPERIMENT Ecosystem type Arctic Subarctic Decomposition and Nutrient Cycling Rates Boreal A Temperate Grassland • Decomposers (detritivores) play a key role in the G Mountain

general pattern of chemical cycling M B,C D P T H,I S E,F O • Rates at which nutrients cycle in different U N L J ecosystems vary greatly, mostly as a result of K Q R differing rates of decomposition RESULTS • The rate of decomposition is controlled by 80 temperature, moisture, and nutrient availability 70 60 R U O 50 K Q T J P 40 S D N F 30 C I M L 20 A H Percent Percent of mass lost B E G 10 0 –15 –10 –5 0 5 10 15 Mean annual temperature ( οοοC)

Figure 55.16c

• Rapid decomposition results in relatively low levels 80 Deforested of nutrients in the soil 60 40 – For example, in a tropical rain forest, material 20 decomposes rapidly and most nutrients are tied Completion of

(mg/L) 4 up in trees other living organisms tree cutting 3 Control • Cold and wet ecosystems store large amounts of 2 undecomposed organic matter as decomposition 1 0 rates are low Nitrateconcentration runoff in 1965 1966 1967 1968 • Decomposition is slow in anaerobic muds (c) Nitrate in runoff from watersheds Figure 55.17 Concept 55.5: Restoration ecologists help return degraded ecosystems to a more natural state

• Given enough time, biological communities can recover from many types of disturbances • seeks to initiate or speed up the recovery of degraded ecosystems

• Two key strategies are bioremediation and (a) In 1991, before restoration (b) In 2000, near the completion of restoration augmentation of ecosystem processes

Figure 55.18 Bioremediation

• Bioremediation is the use of living organisms to 6 detoxify ecosystems ) 5 M • The organisms most often used are prokaryotes, fungi, or plants 4

• These organisms can take up, and sometimes 3 metabolize, toxic molecules

Concentration of 2

– For example, the bacterium Shewanella soluble uranium(

oneidensis can metabolize uranium and other 1 elements to insoluble forms that are less likely to leach into streams and groundwater 0 0 50 100 150 200 250 300 350 400 Days after adding ethanol

Biological Augmentation Restoration Projects Worldwide

• Biological augmentation uses organisms to add • The newness and complexity of restoration essential materials to a degraded require that ecologists consider alternative solutions and adjust approaches – For example, nitrogen-fixing plants can increase based on experience the available nitrogen in soil – For example, adding mycorrhizal fungi can help plants to access nutrients from soil