BIO 311D 1st Edition Lecture 32 Outline of Last Lecture I Signal transduction pathways link signal reception to response II Reception III Transduction IV Response V Post Translational Modification of Preexisting Proteins VI Transcriptional Regulation VII Plant hormones help coordinate growth development and responses to stimuli VIII The Discovery of Plant Hormones IX Auxin X Stem Elongation Outline of Current Lecture I Laws of Thermodynamics II Conservation of Mass III Energy and other limiting factors IV Gross and Net production V Primary Production VI light Limitation VII Nutrient Limitation Current Lecture Ecosystems range from a microcosm such as an aquarium to a large area such as a lake or forest Physical laws govern energy flow and chemical cycling in ecosystems Ecologists study the transformations of energy and matter within ecosystems Conservation 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 heat Conservation 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 that feed 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 levels Energy 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 budget The 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 wavelength Gross 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 CO2 Primary Production in Aquatic Ecosystems In marine and freshwater ecosystems both light and nutrients control primary production Light Limitation Depth of light penetration affects primary production in the photic zone of an ocean or lake Nutrient 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 detergents Primary Production in Terrestrial Ecosystems In terrestrial ecosystems temperature and moisture affect primary production on a large scale 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 production Nutrient 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 other limiting elements Roots have root hairs that increase surface area Many plants release enzymes that increase the availability of limiting nutrients Energy transfer between trophic levels is typically only 10 efficient Secondary