Ben-Gurion University of the Negev. Agroecology. Ecological understanding of farming systems 3. Ecosystem processes

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1 Ben-Gurion University of the Negev Agroecology Ecological understanding of farming systems 3. Ecosystem processes BBoeken Systems Biogeochemical processes Trophic structure Energy and material flows Agroecosystems Effects on energy and material flows Spatial aspects 1

2 Systems A system consists of compartments with links between them. The internal links are stronger than the ones with the environment. Compartment Relationships Organisms Landscape Resources Environment System In an ecosystem organisms form a major compartment The links are Trophic (biogeochemical) relations among organisms and between organisms and abiotic resources Structural relations of organisms with the landscape Redistribution of resources in the landscape. 2

3 Biotic compartments Trophic structure ("Food chains") From autotrophs (plants, algae, cyanobacteria) through various heterotrophic consumers (protists and animals) Consumer/producer and predator/prey interactions Interspecific competition and resource partitioning Not included: Decomposition (by animals, fungi, protists and bacteria) Facilitation Ecosystem engineering Krempels 2005, 3

4 Productivity Net production = net energy incorporated per unit area per unit time Production is a rate (not a state variable) NPP = GPP - R (Gross primary production minus respiration) With each step, only max. 10% is assimilated The rest is used and finally Krempels 2005, lost with respiration as heat. 4

5 Assimilation and respiration The metabolism of the biosphere: trapping, using and disposing energy

6 Energy flow Energy flows through trophic compartments (no cycling) Sizes of compartments depend on input, output and accumulation Heat Carnivores Heat Herbivores Decomposers GPP Primary producers (Plants) Organic matter Rate State After Begon et al

7 Carbon flow Carbon follows the energy pathway through the trophic compartments with some cycling CO 2 CO 2 CO 2 Carnivores Herbivores Decomposers CO 2 Primary producers Organic matter After Begon et al

8 Phosphorous cycle Phosphorus follows two pathways through the trophic compartments: inorganic and organic Slow exchange with the lithosphere, not with the atmosphere, Carnivores Herbivores Micro-organisms Primary producers (Plants) Soil Inorganic P Organic P Rock (P) Oceans (P) 8

9 Nitrogen cycle 5. Denitrification 2N 2 O 2N 2 + O 2 6. Volatilization NH 3 4. Mineralization, Ammonification Organic N NH 3 and NH 4 + Atmosphere (N 2 ) Lightning Carnivores Herbivores Microorganisms 1. Fixation N H e 2NH 3 2. Nitrification Primary producers (Plants) Soil 2NH O 2 2NO H 2 O + 4H + +energy 2NO O 2 2NO energy 3. Assimilation NO 3 - and NH 4 + organic N Uptake Uptake and release, Immobilization Leaching 9

10 N fixation Rhizobium spp (bacterium) on Acacia albida roots Azolla caroliniana (fern) with Anabaena azollae (cyanobacterium)

11 Early humans in ecosystems Consumption of plants and herbivores Reduction of OM Elimination of herbivore competitors, carnivore competitors and predators Humans Atmosphere Plants Consumers Soil Decomposers Used by humans Energy Nutrients 11

12 Agroecosystems Heat Natural ecosystem Carnivores Atmosphere Micro-organisms Energy, Biomass Nutrients Herbivores Primary producers (Plants) Soil and organic matter Agro-ecosystem After Begon et al From natural to agro-ecosystems Heat Export Atmosphere Elimination of carnivores, competing herbivores and plants Reduction of organic matter and decomposition Export of biomass Nutrient inputs Farm animals Crop plants Micro-organisms Soil (+ organic matter) Inputs 12

13 Spatial scale changes Inputs and outputs from/to remote locations In: Nutrients, water, organisms, work, fuel, money Out: Biomass, water, sediment, agrochemicals, money, gases, CO 2, heat. Expansion of area occupied by agroecosystems Extinction of local flora/fauna Habitat fragmentation and destruction Reduction of arrival of natural predators of local pests Ecological footprints Agroecosystem Natural ecosystem 13