Functional aspects of ecosystem
- 1. St. Xavier’s College, Mahuadanr Dr. Emasushan Minj (Assistant Professor) Depatment of Botany Page 1 Functional aspects of ecosystem Unit-9 Core Course-9 Energy Flow The Earth is an open system of energy. It is the key function in the ecosystem. The operation of an ecosystem is regular with the law laws of thermodynamics that deals with the relationship between energy and matter in a system. The behaviour of the energy in the ecosystem is based on two basic laws of thermodynamics. The first law of thermodynamics, which states that energy cannot be created nor destroyed but only transformed. The first law of thermodynamics is also called as law of conservation of energy. The sun is the ultimate source of energy for almost all ecosystems present on the earth. Photosynthetic organisms convert solar energy to chemical energy, but the total amount of energy does not change. The total amount of energy stored in organic molecule synthesized by the process of photosynthesis plus the amounts dissipated as heat must equal the total solar energy intercepted by the photosynthetic organisms. In other words, energy may change form (from radiant to chemical) but not amount. During energy transformation, some amount of energy is converted to form that’s usable. In most cases, this unusable energy takes the form of heat. Energy in the form of heat does not do work it goes to increase the randomness of the universe. The degree of randomness or disorder in the system is known as entropy.
- 2. St. Xavier’s College, Mahuadanr Dr. Emasushan Minj (Assistant Professor) Depatment of Botany Page 2 The second law of thermodynamics, states that every energy transformation that takes place will increase the entropy of the universe in other words, every transformation cannot be hundred percent efficient some energy is always lost as heat. In ecosystems, energy flows unidirectionally. The fraction of incoming solar radiant energy that the producers capture is small. Only about 1- 5% energy is incident solar radiation 2-10% of PAR (Photosynthetically Active Radiant) is actually captured by the photosynthetic processes. The solar energy not used for photosynthesis is immediately converted to heat. The flow of energy through an ecosystem The energy that enters the ecosystem as solar energy (radiant energy) and is then passed a long as chemical energy to successive trophic level. At its step energy is diverted meaning that the chemical energy available to each trophic level is less than that available to the preceding trophic level. Death at each level transfers energy to decomposers. Energy lost as heat at each trophic level is return to the external environment. Energy flow model A simplified representation of energy flow through ecosystem has been made in figure. The model attempts to recognize the various inputs and weights of energy.
- 3. St. Xavier’s College, Mahuadanr Dr. Emasushan Minj (Assistant Professor) Depatment of Botany Page 3 Two aspects with respect to energy flow in the ecosystem need careful consideration. • First, the energy flows unidirectionally, it cannot be transferred in the reverse direction. • Second, the amount of energy flow decreases with successive trophic levels. Ecological efficiencies In ecosystems, living organisms are linked together by feeding relationship. Producers have the ability to fix carbon through photosynthesis via chlorophyll in their leaves. Herbivores are the primary consumers of organic molecule fixed by the producers. Secondary consumers live on the organic molecule of the herbivorous. There may be several levels of carnivorous in any one ecosystem search in such cases the ultimate level will be occupied by the top carnivorous.
- 4. St. Xavier’s College, Mahuadanr Dr. Emasushan Minj (Assistant Professor) Depatment of Botany Page 4 The final groups of organism in an ecosystem are decomposers, bacteria and fungi which can break down the complex organic chemicals of death dead organism or dead material and waste products. Percentage of energy in the biomass produced by one trophic level that is incorporated into the biomass produced by the next higher trophic level is called ecological efficiency. It is also known as transfer efficiency or Lindeman’s efficiency. The proportions of net primary producer production that flow along the possible energy pathways depend on transfer efficiencies in the way energy is used and passed from one step to the next. Knowledge of three categories of transfer efficiency is required to predict the pattern of energy flow. These are consumption efficiency (CE), assimilation efficiency (AE) and production efficiency (PE). Consumption efficiency or exploitation efficiency is the percentage of total productivity available at one trophic level (Pn-1) that is actually consumed by a trophic compartment one level up (In). In the case of secondary consumer, it is the percentage of herbivores productivity eaten by carnivores. Consumption efficiencies of herbivores are very low, reflecting either the difficulty of utilizing plant material or the low herbivores densities. Assimilation efficiency is the percentage of food energy taken into the guts of consumers in a trophic compartment (In) that assimilated across the gut wall (An) and becomes available for incorporation into growth or used to do work. The reminder is lost as feces and enters the base of decomposer system.
- 5. St. Xavier’s College, Mahuadanr Dr. Emasushan Minj (Assistant Professor) Depatment of Botany Page 5 Carnivorous have higher assimilation efficiency approx. 80% than herbivores that is about 20-50% because animal food is more easily digested than plant food. In aquatic ecosystem, autotrophs are mostly of small biomass but very low indigestible matters as compared to their counter parts in the terrestrial ecosystem. Hence, herbivores assimilation efficiency is higher in aquatic ecosystem than in terrestrial ecosystem. Production efficiency is the percentage of assimilated energy (An) that is incorporated into new biomass (Pn). The remainder is entirely lost to the community as respiratory heat. Production efficiency is also known as net productivity efficiency or tissue growth efficiency varies mainly according to taxonomic class of the organism concerned. In vertebrates in general, have high efficiency (30- 40%) and among the vertebrates cold blooded animals have intermediate values of PE around 10%. In warm-blooded animals come with high energy expenditure associated with maintenance maintaining a constant temperature, convert only one to 2% of assimilated energy into production. Similarly, herbivorous tend to have higher production efficiency but lower assimilation efficiency than carnivores. Trophic transfer efficiency Lindeman's law of tropic transfer efficiency or simply tropic efficiency states that the efficiency of energy transfer from one trophic level to the next is about 10% i.e. about 10% off the net primary productivity of producer ends up as herbivores, about 10% of the net productivity of herbivores end up as primary carnivorous and so on. In other words about 90% of energy available at one trophic level typically is not transferred to the next. This loss is multiplied over the length of a food chain. For example, if
- 6. St. Xavier’s College, Mahuadanr Dr. Emasushan Minj (Assistant Professor) Depatment of Botany Page 6 10% of available energy is transferred from primary producers to primary consumers and 10% of that energy is transferred to secondary consumers then only 1% of net primary production is available for next consumer i.e. 10% of 10%. Nutrient cycling Earth is a closed system with respect to matter. Every matter used by living organisms pass between the biotic and abiotic components of biosphere. Nutrient cycling is the movement or cycling movement of matter through the system. It is subdivide the system into to atmosphere, hydrosphere, lithosphere and biosphere. By matter we mean elements such as carbon, nitrogen, oxygen or molecules such as water. The movement of matter between these parts of system is generally termed as a biogeochemical cycle. Gaseous and sedimentary nutrient cycles In gases nutrient cycle, the atmosphere constitutes a major reservoir of element that in a gaseous phase. Such cycle show little or no permanent change in the distribution and abundance of the element. Carbon and hydrogen are main representatives of biogeochemical cycle with a prominent gaseous phase. In a sedimentary cycle, the major reservoir is the lithosphere from where the elements are released by weathering.
- 7. St. Xavier’s College, Mahuadanr Dr. Emasushan Minj (Assistant Professor) Depatment of Botany Page 7 The sedimentary cycles represented by phosphorus, Sulfur, iodine and other biological important elements have a tendency to stagnate. In such cycles, a portion of the supply may accumulate in large quantities as in the deep ocean sediments and thereby become unreachable to organisms and to continual cycle. Some of the elements that are characterized by sedimentary cycle do have a gaseous phase, Sulfur and Iodine, but these phases are insignificant as there is no large gaseous reservoir. Global and local nutrient cycles An elements specific route v biogeochemical cycle varies with particular element and the trophic structure of the ecosystem. There are two general categories of biogeochemical cycle global and local. Gaseous form of carbon, oxygen, Sulfur and nitrogen occur in the atmosphere and cycles of these elements are essentially global. Other, less mobile elements including phosphorus, potassium and calcium are generally cycle in localized scale. Soil is the main abiotic reservoir of these elements. General model of nutrient cycling A general model of nutrient cycling includes the main reservoir of elements and the processes that transferred elements between reservoirs. Each reservoir is defined by characteristics; whether it contains organic or inorganic materials and whether or not the materials are directly available for used by organisms. The nutrients in living organisms and in detritus are available to other organisms when consumers feed and when detritivores consume nonliving organic matter.
- 8. St. Xavier’s College, Mahuadanr Dr. Emasushan Minj (Assistant Professor) Depatment of Botany Page 8 Some materials are moved from the living or organic reservoir to the fossilized organic reservoir, when dead organisms are buried by sedimentation over millions of years becomes coal, peat. The nutrients in these deposits cannot be assimilated directly. Inorganic materials dissolved in water or present in the soil or air are available for use. Organisms assimilate material from this reservoir directly and return chemicals to it through the relatively rapid processes of cellular respiration, excretion and decomposition. Although organisms cannot directly tap into the inorganic elements tied up in the rocks, these nutrients may slowly become available through weathering and erosion. Similarly, unavailable organic materials move into the available reservoir of inorganic nutrients when fossil fuels are burned, releasing exhaust into the atmosphere.
- 9. St. Xavier’s College, Mahuadanr Dr. Emasushan Minj (Assistant Professor) Depatment of Botany Page 9 Carbon cycle Photosynthesis and respiration are the two opposing processes that drive the global carbon cycle. It is predominantly a gaseous cycle with CO2 as the main vehicle of flux between the atmosphere, hydrosphere and biota. Terrestrial plants use atmospheric CO2 as their carbon source for photosynthesis, whereas aquatic plant use dissolved carbonates such as carbon from hydrosphere. In addition, carbon finds its way into Island waters and oceans as bicarbonate resulting from the weathering of calcium rich rock search as limestone and chalk. Respiration by plants, animal and microorganisms release the carbon locked in photosynthetic products back to the atmosphere and hydrosphere carbon compartments.
- 10. St. Xavier’s College, Mahuadanr Dr. Emasushan Minj (Assistant Professor) Depatment of Botany Page 10 Nitrogen cycle The atmospheric phase is major in the global net nitrogen cycle. In nitrogen cycle nitrogen is converted between its various chemical forms. This transformation carried out by both biological and non biological processes. The important processes in the nitrogen cycle include nitrogen fixation ammonia fixation, nitrification and denitrification. Nitrogen fixing involves the conversion of N2 by bacteria to ammonium ions. Atmospheric nitrogen is also fixed by lightning discharge during storm and reaches the ground as nitric acid dissolved in rainwater but only about 3-4% of fixed nitrogen derives from this pathway. Ammonification involves decomposition of organic nitrogen to ammonium ion. In nitrification, ammonium ion is converted to nitrate nitrite and nitrate by nitrifying bacteria. Denitrification is the reduction of nitrates into nitrogen gas. The process is performed by bacterial species such as pseudomonas and clostridium in anaerobic conditions.
- 11. St. Xavier’s College, Mahuadanr Dr. Emasushan Minj (Assistant Professor) Depatment of Botany Page 11 Phosphorus cycle Phosphorus occur in rocks and ocean sediments and in dissolved form in rivers, lake and ocean water. Weathering of rock gradually adds phosphorus to soil some leached into groundwater and surface water and main event will reach the sea. The phosphorus cycle may be described as an ‘open’ cycle because of the general tendency of mineral phosphorus to be carried from the land to the ocean. A typical phosphorus atom released from the rocks by chemical weathering may enter and cycle within the terrestrial community for years, or centuries before it is carried via groundwater into a stream, where it takes part in the nutrient spiraling.
- 12. St. Xavier’s College, Mahuadanr Dr. Emasushan Minj (Assistant Professor) Depatment of Botany Page 12 Sulfur cycle In the global phosphorus cycle, lithospheric phase is predominant whereas in the nitrogen cycle, atmospheric phase is more important. Sulfur by contrast has atmospheric and ethers ferric phases of similar magnitude. Three natural biogeochemical cycle processes release sulfur into the atmosphere: • The formation of volatile compound dimethyl sulfide • Anaerobic respiration bi sulfate reducing bacteria and • Volcanic activity The weathering of rocks provides about half the sulfur draining of the land into rivers and lakes the reminder driving from atmospheric sources. The sulfur takes taken up taken up by plants; past along food chain and wire decomposition processes becomes available again to the plants. The combustion of fossil fuel is the major human activity e to the global sulfur cycle.
- 13. St. Xavier’s College, Mahuadanr Dr. Emasushan Minj (Assistant Professor) Depatment of Botany Page 13 Summary In the flow of energy and inorganic nutrients through the ecosystem of few generalizations can be made: ➢ The ultimate source of energy is the sun. ➢ The ultimate fate of energy in ecosystem is to be lost as heat. ➢ Energy and nutrients are passed from organism to organism through the food chain as one organism eats another. ➢ Decomposers remove the last energy from the remains of organisms. ➢ In organic nutrients are cycle, energy is not.