1Carbon cycle• CO2+ H2O → CH2O + O2• Carbohydrates used for– Respiration– Add biomass– Supply upper trophiclevels• Ultimate energy supply for all ecosystemsCarbon cycle• Carbon Sinks– Ocean– Atmosphere– Plant biomass– Animal biomass– Sediment– Detritus• Climate change implicationsGlobal Sink Size Carbon cycle and fossil fuels• Increase in atmospheric CO2since industrial revolution2Phosphorus Cycle• Necessary for protein production• Inorganic P (PO4) taken up by plants• Plant-fungi mutualism increases uptake• Organic P moves through foodweb, animal and decomposers release inorganic P• Freshwater ecosystems often P limited• Sediments are P sinks• Weathering of soil provides some PNitrogen Cycle• Most common element in atmosphere• Few organisms can fix N2• Fixed N often limiting in terrestrial systemsNitrogen cycle• N2H4CO + H2O → 2NH3+ CO2• NH3+ H2O → NH4++ OH-• NH4+ → NO2-→ NO3-• Most animals produce ammonia (NH3) or urea (N2H4CO) as nitrogenous waste• Plants can only use ammonium (NH4) or nitrite (NO3)• Nitrifying bacteria (Nitrosomonas and Nitrobacter) –convert amonium, nitrate (NO2) to nitrite (NO3)• Denitrifying bacteria complete the cycle NO3→ N2Decomposers• All nutrient cycles rely on decomposers to process waste, make nutrients available again.• Without decomposers – residence times increase, organic matter accumulates, nutrient availability declines3Fertilizers• Primary productivity often limited by a single nutrient• Boost nutrient availability in a limited area to increase productivity• N-P-K ratioRed TideNutrient influx to marine systems from human activitiesShift nutrient dynamics to favor one speciesNutrient export and ecosystem function• Ecosystems are not closed systems, but usually have balanced nutrient import/export• Disturbances can change dynamic and alter productionDeforestation • Increased erosion• Increased nutrient export• Decreased nutrient content in soils• Decreased productivity• Nutrient increase in aquatic system, freshwater and marine4Energetics• All ecosystem energy is ultimately solarSpecific wavelength absorption by atmospheric componentsPrimary Productivity• Primary productivity – amount of energy or biomass produced by photosynthesis in an ecosystem.– Autotrophs - Plants, bacteria and photosynthetic protists (algae)– Measured as biomass or energy (calories)– Serves as food for all non-photosynthetic life (heterotrophs)– Mixotrophs – can switch between auto and heterotrophic.• CO2+ H2O → CH2O + O2Water absorption of wavelengths• Blue and green penetrate well• Red and orange are absorbed quickly5Photosynthetically Active Radiation (PAR)• Wavelengths used for photosynthesis• Chlorophyll – violet and red• Secondary compounds absorb yellow and orange– Carotenoids– Xanthophyl– Phycobillin• Nothing efficiently uses greenPhotosynthesis• Light reactions– Chlorophyll captures light energy– Water split, O2released• Dark reactions– Atmospheric CO2converted to carbohydratesC3 carbon fixation• CO2taken directly from air• CO2fixed directly by enzyme rubisco• Rubisco can also act on O2, reducing CO2fixation rate (photorespiration)C4 carbon fixation• C3 pathway restricted to deeper portion of leaf• CO2stored in malate (C4), stomata open less• Dark reactions pull CO2from malate, fix it to carbohydrates• Dark reactions similar to C3. except for source of C• Minimize photorespiration• Less nitrogen required (less rubisco)6CAM photosynthesis• Crassulacean acid metabolism (CAM)• Desert adapted plants• Modified C4• Stomata open at night only, store C in malic acid• Thick cuticle on leaves• Water storage helps deal with malic acid • No photorespirationC3 C4 CAM overview• C3– Most plants– Need stomata open to complete cycle with CO2. – When stomata closed, use O2through photorespiration– 18 ATP used to synthesize one glucose, up to half of the energy from light reaction spent in photorespiration• C4– More efficient CO2uptake, stomata not open as long– Each CO2is fixed twice– Advantageous in dry, hot, or CO2limiting conditions– 30 ATP used to synthesize one glucose, photorespiration minimized• CAM– Similar to C4– Photorespiration avoidedDistribution of C4 plants Products of Photosynthesis• Carbohydrates wind up in one of three places– Used immediately in respiration– Stored and used later in respiration– Used to build plant biomass – ultimately used later in repiration• Carbon fixed by photosynthesis is all ultimately used for respiration– Carbon cycle– Plant biomass as a carbon sink7Primary production efficiency• What percentage of solar energy is converted to usable energy in carbohydrates?– Limited wavelengths used– Energy spent during process or respiration (30%)– 1-2% on land 3-4% for algae– Solar constant 1366 watts/m2– Efficient solar panels = 15%Light, moisture, nutrients and CO2as resources• All are “food”, photosynthetic organisms compete for them. One is often limiting.Primary ProductionPrimary ConsumerSecondary ConsumerTertiary ConsumerEltonian Pyramid• Primary production determines energy available for herbivores (primary consumers)• Lindeman efficiency = proportion of total energy passed from one trophic level to the next.• 10% efficiency is typicalWhy so inefficient?• First law of thermodynamics – conservation of energy• Second law of thermodynamics – quality of energy declines as it is transferred from one state to the next• Entropy – systems naturally progress towards a state of disorder. At every level, a higher portion of the energy exists in a disordered state.• Most energy “lost” as kinetic energy or heat8Primary producer – herbivore inefficiency• Plant defenses– Physical• Spines, silica– Chemical• Alkaloids, Terpenoids, tannins, nicotine, caffeine– Low food quality• Similar to other predator-prey relationships• Coevolved, “evolutionary cat and mouse”Simple terrestrial tropic levelsPrimary ProductionPrimary ConsumerSecondary ConsumerTertiary ConsumerEltonian Pyramid• All ecosystems should be dominated (biomass or energy) by primary producers, then by decomposers.Biomass from all levelsavailable to detritivores.9More energy in and/or greater efficiency should result in more trophic levels.Exploitation Efficiency• Proportion of available energy at a lower level