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Plant Ecology - Chapter 14 Ecosystem Processes
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Ecosystem Ecology Focus on what regulates pools (quantities stored) and fluxes (flows) of materials and energy in abiotic and biotic components
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Ecosystem Ecology Turnover time - how rapidly does it move through the system Retention time - how long does it reside in a component
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Ecosystem Ecology Pools, fluxes connected together into biogeochemical cycles Biology, geology, chemistry interconnected
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Ecosystem Ecology Plants under the influence of some cycles, influence others Water, oxygen, carbon, nitrogen, phosphorus, sulfur, potassium
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Water Cycle
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Terrestrial plants are only living things to have significant effect on water cycle Evapotranspiration from plants can provide huge proportion of moisture in atmosphere - affect rainfall patterns
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Water Cycle Cutting rainforests can result in decreased evapotranspiration, decreased rainfall, increased air temperatures at ground surface
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Water Cycle Since plants intercept rainfall, reduce its impact on ground, removing vegetation can alter infiltration/runoff relations
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Water Cycle Even removing vegetation in semi- arid regions can reduce rainfall, increase soil temperatures, induce onset of desertification
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Water Cycle Flux differences among, within biomes
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Water Cycle Potential evapotranspiration (PET) - water lost via this process if water is freely available and plant cover is 100% Actual evapotranspiration (AET) - precipitation minus runoff and infiltration PET>AET in dry climates PET=AET in intact tropical rain forests AET linked to productivity, decomposition
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Carbon Cycle Primary productivity - rate of transfer of inorganic C from atmosphere into organic C in plants via photosynthesis
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Carbon Cycle NPP - dry metric tons/ha/yr
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Productivity Different ecosystems - related to leaf biomass Different forests - latitude, climate, elevation
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Productivity
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Estimating Productivity Standing biomass after a growing season Drawbacks: destructive, and ignores belowground productivity (can be majority in some plants)
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Estimating Productivity Indirect measures: develop formulae for relating plant size changes to biomass changes Allometric relationships used by timber companies, forest ecologists Drawback: formula needed for each species
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Estimating Productivity Indirect measures: use relation between productivity and AET Fairly good estimates of productivity over broad range of climates Drawback: poor predictor of productivity where precipitation and temperature are both high
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Estimating Productivity Remote sensing - use reflectance of light wavelengths by chlorophyll to estimate productivity Normalized difference vegetation index (NDVI) - good correlation between NDVI and NPP ground measurements NDVI = NIR-VIS NIR+VIS
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Decomposition Dead stuff becomes soil organic matter, then via mineralization becomes inorganic nutrients, CO 2, water, and energy
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Decomposition - Saprophytic fungi are the major decomposers of dead leaves, plant litter - Bacteria also essential, but only in latter stages
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Decomposition Decomposition largely an aerobic process - very slow in waterlogged, cold soils Physical, chemical characteristics also affect rate of decomposition Root decomposition of soft and hardwoods
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Net Ecosystem Production NEP is net accumulation of carbon per year by ecosystem Positive during growing season, negative during non- growing season
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Net Ecosystem Production Undisturbed ecosystems usually show small, positive accumulations of C each year Accumulation of woody tissue in long-lived plants
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Soil Carbon: Pools and Fluxes
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Nitrogen & Productivity
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Nitrogen Cycle - Rapid flux through living organisms - Large global pool with slow turnover
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Phosphorus Cycle - Does not have major atmospheric pool like other cycles - Mostly recycled in organic form through other living organisms
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Calcium Cycle Sedimentary cycle Needed by plants for chemical (growth, stress regulation), structural (support) roles Largely lost in leaf fall - must be replaced each year
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Calcium Cycle Calcium depletion occurring in many forests today Acid deposition displaces soil calcium, logging removes it Decreased growth, higher mortality (more susceptible to pathogens)
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