Chapter 54 Ecosystem I Ecosystems, Energy and Matter A. General Information 1. Ecosystems – all the organisms living in a community as well as the abiotic factors with which they interact 2. Energy flow and chemical cycling are important in the study of ecosystem a. energy enters the system in the form of sunlight and is converted to chemical energy by autotrophs and is passed to heterotrophs in the form of food and dissipated in the form of heat b. chemical elements such as carbon and nitrogen are cycled among abiotic and biotic components of the ecosystems

B. Thermodynamics – the study of energy transformations 1. First Law of Thermodynamics – energy can be transferred and transformed, but it cannot be created or destroyed 2. Second Law of Thermodynamics – energy transfer or transformation makes the universe more disordered a. energy conversion can’t be efficient, some energy is lost as heat b. energy flowing through ecosystems is dissipated into space as heat

II Trophic Relationships – each ecosystem has a trophic structure of feeding relationships that determine the paths of energy flow and chemical cycling A. Trophic Levels 1. Primary producers 2. Primary consumers 3. Secondary consumers 4. Tertiary consumers 5. Decomposers (detritivores) a. prokaryotes, fungi, and animals that get their energy from detritus b. detritivores decompose the organic materials and transfer the chemical elements in inorganic form to soil, water, and air c. producers recycle the elements into organic compounds

III Ecosystem energy budget A. Global energy budget 1. most of the solar radiation is reflected, absorbed, or scattered by the atmosphere, clouds, and dust 2. only a small amount of solar energy strikes plants and algae B. Gross and Primary Production 1.GPP - total primary production in an ecosystem, the amount of light energy that is converted to chemical energy by photosynthesis

2. Net primary production – is equal to gross primary production minus the energy used by the primary producers for respiration a. accounts for the organic mass of plants and represents storage of chemical energy available for consumers b. can be expressed as biomass 3. primary productivity varies among ecosystems a. tropical rainforest are very productive and contribute large portion to overall productivity b. estuaries and coral reefs are also productive but make only a small contribution to productivity c. open oceans have low productivity but make the largest contribution to ecosystems d. deserts and tundra have low productivity

C. Limiting Factors in Aquatic ecosystem productivity 1. light intensity and temperature affect primary productivity of phytoplankton in the open ocean -productivity is highest near the surface and decreases with depth 2. nutrient limitation – in open ocean water there is low concentration of phosphorus and nitrogen in the photic zone 3. marine phytoplankton is most productive where up- dwellings bring nutrient rich waters to the surface 4. freshwater ecosystem productivity varies from the surface to the depths in relation to light intensity -biannual turnovers bring nutrients to the surface waters

IV Biogeochemical Cycles A. Gen Information 1. Continuation of life depends on recycling of essential chemical elements 2. Decomposition of wastes and the remains of dead organisms replenishes the pool of inorganic nutrients available to autotrophs 3. Biogeochemical cycles = nutrient circuits involving both biotic and abiotic components of ecosystems 4. Elements such as carbon, oxygen, sulfur, and nitrogen have gaseous forms, their cycles are global and the atmosphere serves as a reservoir

a. characteristics that define reservoirs 1. whether they contain organic or inorganic materials 2. whether or not the materials are directly available for use by organisms b. available organic reservoirs contains living organisms and detritus (available when organisms feed on each other) c. the unavailable organic reservoir is formed by organisms that died ( coal, oil, and peat) d. the available inorganic reservoirs includes all matter present the soil or air and dissolved in water

B Types of geochemical cycles 1. Water Cycle – occurs between the oceans and the atmosphere a. solar energy results in evaporation from oceans b. water vapor rises, cools, and falls as precipitation c. over the oceans, evaporation exceeds precipitation excess water vapor is moved over land by winds d. over land, precipitation exceeds evaporation and transpiration, runoff and ground water balance the net flow of water vapor to land e. the water cycle is primarily due to physical processes, not chemical

2. The Carbon Cycle – autotrophs acquire carbon dioxide from the atmosphere by diffusion through leaf stomata, some becomes a carbon source for consumers, and respiration returns carbon dioxide to the atmosphere a. carbon loss by photosynthesis is balanced by carbon release during respiration b. atmospheric carbon dioxide is increased by combustion of fossil fuel c. the amount of atmospheric CO 2 decreases in the Northern Hemisphere during the summer due to increased photosynthetic activity and increase in the winter when respiration exceeds photosynthesis

3. The Nitrogen Cycle – nitrogen is the key chemical in ecosystems; its found in all amino acids which comprise the proteins of organisms a. 80% of the atmosphere is made of N 2, but it’s not available to plants b. nitrogen enters ecosystems by either atmospheric deposition or nitrogen fixation 1. atmospheric deposition of nitrogen - NH 4 + (ammonium) and NO 3 (nitrate) are added to the soil by being dissolved in rain or by settling as part of fine dust 2. nitrogen fixation – the reduction of atmospheric nitrogen to ammonia(NH 3 )which can be synthesize nitrogenous organic compounds such as amino acids

a. only certain prokaryotes can fix nitrogen 1. terrestrial – some nonsymbiotic soil bacteria and symbiotic (Rhizobium) soil bacteria 2. Cyanobacteria fix nitrogen in aquatic ecosystems b. -NH 3 is a gas and can evaporate quickly in the atmosphere -NH 4 can be used directly by plants c. the nitrogen cycle also involves -nitrification – a metabolic process by which aerobic soil bacteria use ammonium (NH 4 + ) as an energy source by oxidizing it to nitrite (NO 2 ) and then to nitrate (NO 3 - )

Plants assimilate nitrate and convert it to organic forms of amino acids and proteins. Animals assimilate organic nitrogen by eating plants and other animals - denitrification – process that returns nitrogen to the atmosphere by converting NO 3 to N 2 -Ammonification – the decompositition of organic nitrogen back to ammonia

Important aspects of the Nitrogen Cycle 1. Prokaryotes serve as vital links in the cycle 2. Most of the nitrogen cycling involves nitrogenous compounds in the soil and water 3. Many species of plants depend on symbiotic, nitrogen- fixing bacteria in their root nodules as a source of nitrogen in a form that can be assimilated 4. Denitrification only return a small amount of Nitrogen back to the atmosphere 5. Most assimilate nitrogen comes from nitrate 6. The majority of nitrogen in most ecosystem is recycled by decomposition and reassimilation

4. The Phosphorous Cycle -a major component of nucleic acids, phospholipids, ATP, and a mineral in bone and teeth -Phosphorous Cycle a. weathering of rocks adds Phosphorous to the soil b. producers absorbs the soil phosphate c. phosphorous is transferred to consumers in organic forms d. phosphorous is added back to the soil by excretion and decomposition of detritus e. phosphorous may limit algal productivity in aquatic habitat