BIO 311D 1st Edition Lecture 32Outline of Last Lecture I. Signal transduction pathways link signal reception to responseII. ReceptionIII. TransductionIV. ResponseV. Post-Translational Modification of Preexisting ProteinsVI. Transcriptional RegulationVII. Plant hormones help coordinate growth, development, and responses to stimuliVIII. The Discovery of Plant HormonesIX. AuxinX. Stem ElongationOutline of Current Lecture I. Laws of ThermodynamicsII. Conservation of MassIII. Energy and other limiting factorsIV. Gross and Net productionV. Primary ProductionVI. light LimitationVII. Nutrient LimitationCurrent Lecture• Ecosystems range from a microcosm, such as an aquarium, to a large area, such as a lakeor forestPhysical laws govern energy flow and chemical cycling in ecosystems• Ecologists study the transformations of energy and matter within ecosystemsConservation of Energy• Laws of physics and chemistry apply to ecosystems, particularly energy flow• 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• The second law of thermodynamics states that every exchange of energy increases the entropy of the universe• In an ecosystem, energy conversions are not completely efficient, and some energy is always lost as heatConservation of Mass• The law of conservation of mass states that matter cannot be created or destroyed• Chemical elements are continually recycled within ecosystems• In a forest ecosystem, most nutrients enter as dust or solutes in rain and are carried away in water• Ecosystems are open systems, absorbing energy and mass and releasing heat and waste products• Autotrophs build molecules themselves using photosynthesis or chemosynthesis as an energy source• Heterotrophs depend on the biosynthetic output of other organisms• Energy and nutrients pass from primary producers (autotrophs) to primary consumers (herbivores) to secondary consumers (carnivores) to tertiary consumers (carnivores thatfeed on other carnivores) • Detritivores, or decomposers, are consumers that derive their energy from detritus, nonliving organic matter• Prokaryotes and fungi are important detritivores• Decomposition connects all trophic levelsEnergy and other limiting factors control primary production in ecosystems• 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 extent of photosynthetic production sets the spending limit for an ecosystem’s energy budgetThe Global Energy Budget• The amount of solar radiation reaching Earth’s surface limits the photosynthetic output of ecosystems• Only a small fraction of solar energy actually strikes photosynthetic organisms, and even less is of a usable wavelengthGross and Net Production• Total primary production is known as the ecosystem’s gross primary production (GPP)• GPP is measured as the conversion of chemical energy from photosynthesis per unit time• 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/m2×yr), or Biomass added per unit area per unit time (g/m2×yr)• NPP is the amount of new biomass added in a given time period• Only NPP is available to consumers• Standing crop is the total biomass of photosynthetic autotrophs at a given time• Ecosystems vary greatly in NPP and contribution to the total NPP on Earth• Tropical rain forests, estuaries, and coral reefs are among the most productive ecosystems per unit area• Marine ecosystems are relatively unproductive per unit area but contribute much to global net primary production because of their volume• Net ecosystem production (NEP) is a measure of the total biomass accumulation during a given period• NEP is gross primary production minus the total respiration of all organisms (producers and consumers) in an ecosystem• NEP is estimated by comparing the net flux of CO2 and O2 in an ecosystem, two molecules connected by photosynthesis• The release of O2 by a system is an indication that it is also storing CO2Primary Production in Aquatic Ecosystems• In marine and freshwater ecosystems, both light and nutrients control primary productionLight Limitation• Depth of light penetration affects primary production in the photic zone of an ocean or lakeNutrient Limitation• Experiments in the Sargasso Sea in the subtropical Atlantic Ocean showed that iron limited primary production• More than light, nutrients limit primary production in geographic regions of the ocean and in lakes• A limiting nutrient is the element that must be added for production to increase in an area• Nitrogen and phosphorous are the nutrients that most often limit marine production• Nutrient enrichment experiments confirmed that nitrogen was limiting phytoplankton growth off the shore of Long Island, New York• Upwelling of nutrient-rich waters in parts of the oceans contributes to regions of high primary production• The addition of large amounts of nutrients to lakes has a wide range of ecological impacts• In some areas, sewage runoff has caused eutrophication of lakes, which can lead to loss of most fish species• In lakes, phosphorus limits cyanobacterial growth more often than nitrogen• This has led to the use of phosphate-free detergentsPrimary Production in TerrestrialEcosystems• In terrestrial ecosystems, temperature and moisture affect primary production on a largescale• Primary production increases with moisture• Actual evapotranspiration is the water transpired by plants and evaporated from a landscape• It is affected by precipitation, temperature, and solar energy• It is related to net primary productionNutrient Limitations and Adaptations That Reduce Them• On a more local scale, a soil nutrient is often the limiting factor in primary production• In terrestrial ecosystems, nitrogen is the most common limiting nutrient• Phosphorus can also be a limiting nutrient, especially in older soils• Various adaptations help plants access limiting nutrients from soil• Some plants form mutualisms with nitrogen-fixing bacteria• Many plants form mutualisms with mycorrhizal fungi; these fungi supply plants with phosphorus and