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in Energy Agroecosystems Carbon and Energy in Ecosystems Movement of carbon and energy through ecosystems is closely linked. Organic compounds: contain carbon sources of potential energy Therefore, we can track carbon and energy simultaneously. Photosynthesis 6 CO 2 + 6 H 2 O light C 6H12 O 6 + 6 O 2 Organic molecules contain: C Energy Both now incorporated into living plant system Respiration C 6H12 O 6 + 6 O 2 6 CO 2 + 6 H2 O Energy is released (for use by organisms) 2 C is released as CO C and energy cycles are completed Energy Tracks Similar to Carbon Flow in Ecosystems Energy in Ecosystems Energy is a common denominator to all individuals in an ecosystem. All living organisms and their products (wood, oil, etc.) contain various amounts (kcal) of potential energy stored in their tissues. Can standardize for comparisons in terms of energy. Removing water from organisms yields biomass from which you can calculate its energy equivalent. 1. Energy or Trophic Pyramid Production Respiration Plant often less than 1-2% efficient at harvesting light Sunlight Primary Producer Plant = primary producer Gross primary production (GPP) = total energy captured by plant during photosynthesis. GPP is used for: Respiration (R) to maintain life functions of the plant. Production (P) = Net primary production (NPP) for plants = energy which is stored in plant tissues (growth, etc.) -- estimated from dry biomass produced over time. Note that GPP = NPP + R. Energy Transfer Efficiency Efficiency of transfer of energy from solar energy to NPP is low (<4%). Price, 1997. Insect Ecology; see also Tivy, 1992. Energy or Trophic Pyramid Secondary consumer Assimilated P R NA Primary consumer Consumed Production Respiration Plant Sunlight Energy Consumed Several outcomes from energy consumed (C): Non-assimilated (NA) - some energy is never assimilated by the animal, but is passed through the digestive system and excreted. Assimilated (A) - energy actually used by the consumer for respiration and production. Note that for consumers, A = P + R, and C = A + NA = P + R + NA. Consumers Consumer = obtains energy from other organisms. Primary consumer - feeds on plants Secondary consumer - feeds on primary consumers. Consumers obtain energy from P of organisms immediately below them. Efficiency of transfer between trophic levels varies but 10% is rough estimate (see Odum, 1983). Energy or Trophic Pyramid Secondary consumer Assimilated P R NA Primary consumer Consumed Production Respiration Plant Sunlight Allocation of Assimilated Energy Plants about 50% for P/A Most insects 35-45% for P/A Social insects < 10% for P/A Endotherms < 10% for P/A Birds 1-2% for P/A Predators have lower P/A than herbivores. Endotherms have low P/A Depends on lifestyle and activity of organism 1. Energy or Trophic Pyramid Secondary consumer Assimilated P R NA Primary consumer About 10% energy between levels Plant less than 1-2% efficient at harvesting light Consumed Production Respiration Sunlight Trophic Pyramid Trophic pyramid - energy transfers upward through layers (= trophic levels) of a pyramid. Since energy transfer is never 100% efficient, amount of energy for P and R decreases moving up to higher levels, so organisms at higher levels cannot use more energy than those at lower levels. NOTE SIMILAR SHAPE FOR CARBON FLOW! Special Considerations for Energy Production is measured in kcal/m2/yr, or some equiv. units considering area and time. Standing crop = energy in equivalent living tissue available at some specific time (kcal/m2). e.g., plant harvest or insects collected at one point in time. Note that standing crop (energy measured at one time) may be different from production (energy produced over time). e.g., if multiple harvests occur, or if multiple generations per year. Special Considerations for Energy Units vary in different scientific disciplines; engineering uses joule: 4.19 J = 1.0 cal Energy is a common denominator: Same units for photosynthesis to herbivores through carnivores in trophic pyramids. Various operations (pest control, work, etc.) can be estimated so that these can be included with energy equivalent of materials in overall energy budget. Food Webs Trophic pyramid is oversimplified (hot topic in 1942!). Unrealistic way to track energy flow in ecosystems. Food web: Shows multiple connections among organisms within ecosystem. More realistic. Above-ground Food Webs relatively simple Note: Predator feeding at multiple trophic levels Price. 1997. Insect Ecology Above-ground Food Webs - very complex Price - Fig. 22.16 Below-ground Food Webs This is now known to be a very important component of the ecosystem food web that was often ignored. Much food originates from plant. from living plant tissues (into pests). from dead plant material (into decomposers). Interconnection of Food Webs Above- and below-ground systems are connected Food webs from different ecosystems are interconnected Energy Follows Carbon Flow in Ecosystems Solar = Direct energy input Indirect energy Indirect Energy (not given directly to plant) Not only fuel, but Fertilizers (require energy to make) Pesticides (require energy to make) Irrigation (energy for pumps, etc.) Improved crop varieties (may require more energy intensive management) Indirect Energy Input Saves plant energy Plant can put saved energy into Production Energy Herbicide Kills weeds Saves plants from wasting energy on competition Agroecosystems consume energy (because harvest is removed), Especially if external indirect energy is supplied to make plant production more efficient Energy and Maximization of Yield Yield maximized by increasing: Harvest index = % of biomass actually used; can be increased with management (over time through plant breeding, etc.) Plant population (including multiple cropping in time and space) Plant size (more biomass per unit of land) Plant Size and Yield Increased by Increased Energy Input: Corn Yields in US Limits to yield per ha -- levels off Fertilizer Use in US Energy Inputs/Outputs for 1 ha of Corn in US (Carroll, 1990) 1910 Labor (hrs) 120 Energy use 1301 (1000 kcal/ha) 1950 44 3107 2383 1980 12 10,384 6500 Yield (kg/ha) 1880 Energy Inputs/Outputs for 1 ha of Corn in US (Carroll, 1990) 1910 Labor (hrs) 120 Energy use 1301 (1000 kcal/ha) 1950 44 3107 2383 0.77 1980 12 10,384 6500 0.63 Yield 1880 (kg/ha) Yield per 1.44 Energy unit Energy Inputs/Outputs for 1 ha of Corn in US (Carroll, 1990) 1910 Labor (hrs) 120 Energy use 1301 (1000 kcal/ha) 1950 44 3107 2383 0.77 1980 12 10,384 6500 Max production 0.63 Yield 1880 (kg/ha) Yield per 1.44 Max Energy unit Efficiency Energy Challenge Cant increase yields indefinitely through energy input Maintain yield and production (or even increase as population increases) Reduce inputs (as less inputs are available) References Text, pp. 20-31. Carroll et al., 1990. Ch. 5. Odum, 1983. Ch. 3. Price, 1997. Insect Ecology. John Wiley, New York. Tivy, 1992. Ch. 6. ... View Full Document

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