7 - Productivity theory - higher plant productivity...

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Unformatted text preview: Productivity theory - higher plant productivity supports bigger longer food chain - increase plant productivity supports higher consumer diversity- food web dynamics may influence biodiversity Energy flow through ecological communities 1) plants = primary producers primary production – rate at which plant biomass is produced 'per unit area‘ by photosynthesis biomass = weight of an organism per unit area of ground or water (standing crop )- biomass units: dry organic matter (kg m 2 or kg C m 2 ) or energy (joules m 2 )- units of productivity: (kg C m-2 day-2 ) or energy (joules m-2 day-2 )- measurement of carbon difficult: usually dry weight 2) gross primary production = net primary production + respiration GPP = NPP + R NPP = actual plant growth = plant biomass available to heterotrophs (herbivores) Patterns in primary production 1. production on land - latitudinal trend of increase NPP from tundra to tropic 2. production in ocean - no clear latitudinal trend- limited by nutrients- highest in coastal oceans 3. production per unit area is much higher on land- low values in open oceans - open oceans similar to deserts & tundra- high productivity in upwellings & estuaries Factors limiting primary productivity Terrestrial communities 1) Light- 44% of solar energy is at wavelength suitable for photosynthesis GPP efficiency = energy fixed in photosynthesis / energy in incident sunlight- usually < 1.0% in plant communities- 3- 10% in crop plants over short periods under ideal conditions- 50- 70% of GPP is lost to respiration- NPP usually << 1% of sun's energy- light can be limiting even though it is inefficiently used eg. NPP in deciduous forest in N. America & length of growing season Factors limiting primary productivity Terrestrial communities 1) Light 2) Precipitation- NPP correlated with mean annual precipitation Factors limiting primary productivity Terrestrial communities 1) Light 2) Precipitation 3) Temperature- NPP is usually related to temperature althought the relationship may be complex Responses of plant to change in temperature- photosynthesis increases with temperature & reaches plateau or even declines- respiration increases exponentially with temperature - NPP = GPP - R- maximum net photosynthesis & plant growth (NPP) occurs at intermediate temperature- optimal temperature for plant growth < optimal temperature for photosynthesis Evapotranspiration = water loss via evaporation & transpiration- productivity increased with evapotranspiration- highest in tropical forest, lowest in desert & tundra- largely explains pattern of NPP on land NPP highest in warm temperature + adequate water supply for high transpiration Factors limiting primary productivity Terrestrial communities 1) Light 2) Precipitation 3) Temperature 4) Nutrients- most important factor on plant productivity = fixed nitrogen- nitrogen is limited in most oceans- few marine organisms can fix nitrogen- productivity in most ecosystems can be increased by addition of nitrogen Production of salt marsh sedges...
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This note was uploaded on 09/26/2010 for the course ENG ELT1106 taught by Professor Mei during the Spring '07 term at 한동대학교.

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7 - Productivity theory - higher plant productivity...

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