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Plant Ecology - Chapter 14
Ecosystem Processes
Ecosystem Ecology
Focus on what regulates pools (quantities stored) and fluxes (flows) of materials and energy in abiotic and biotic components
Ecosystem Ecology
Turnover time - how rapidly does it move through the systemRetention time - how long does it reside in a component
Ecosystem Ecology
Pools, fluxes connected together into biogeochemical cyclesBiology, geology, chemistry interconnected
Ecosystem Ecology
Plants under the influence of some cycles, influence othersWater, oxygen, carbon, nitrogen, phosphorus, sulfur, potassium
Water Cycle
Water Cycle
Terrestrial plants are only living things to have significant effect on water cycleEvapotranspiration from plants can provide huge proportion of moisture in atmosphere - affect rainfall patterns
Water Cycle
Cutting rainforests can result in decreased evapotranspiration, decreased rainfall, increased air temperatures at ground surface
Water Cycle
Since plants intercept rainfall, reduce its impact on ground, removing vegetation can alter infiltration/runoff relations
Water Cycle
Even removing vegetation in semi-arid regions can reduce rainfall, increase soil temperatures, induce onset of desertification
Water CycleFlux differencesamong, within biomes
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 infiltrationPET>AET in dry climatesPET=AET in intact tropical rain forestsAET linked to productivity, decomposition
Carbon CyclePrimary productivity - rate oftransfer of inorganic C fromatmosphere into organic Cin plants via photosynthesis
Carbon Cycle
NPP -dry metric tons/ha/yr
ProductivityDifferent ecosystems -related to leaf biomass
Different forests - latitude,climate, elevation
Productivity
Estimating Productivity
Standing biomass after a growing seasonDrawbacks: destructive, and ignores belowground productivity (can be majority in some plants)
Estimating Productivity
Indirect measures: develop formulae for relating plant size changes to biomass changesAllometric relationships used by timber companies, forest ecologistsDrawback: formula needed for each species
Estimating Productivity
Indirect measures: use relation between productivity and AETFairly good estimates of productivity over broad range of climatesDrawback: poor predictor of productivity where precipitation and temperature are both high
Estimating Productivity
Remote sensing - use reflectance of light wavelengths by chlorophyll to estimate productivityNormalized difference vegetation index (NDVI) - good correlation between NDVI and NPP ground measurements
NDVI = NIR-VIS NIR+VIS
DecompositionDead stuff becomes soil organic matter, then viamineralization becomes inorganic nutrients, CO2,water, and energy
Decomposition- Saprophytic fungi are the major decomposers of dead leaves, plant litter- Bacteria also essential, but only in latter stages
Decomposition
Decomposition largely an aerobic process - very slow in waterlogged, cold soilsPhysical, chemical characteristics also affect rate of decomposition
Root decomposition ofsoft and hardwoods
Net Ecosystem Production
NEP is net accumulation of carbon per year by ecosystemPositive during growing season, negative during non-growing season
Net Ecosystem Production
Undisturbed ecosystems usually show small, positive accumulations of C each yearAccumulation of woody tissue in long-lived plants
Soil Carbon: Pools and Fluxes
Nitrogen & Productivity
Nitrogen Cycle- Rapid flux through living organisms- Large global pool with slow turnover
Phosphorus Cycle- Does not have major atmospheric pool like other cycles- Mostly recycled in organic form through other living organisms
Calcium Cycle
Sedimentary cycleNeeded by plants for chemical (growth, stress regulation), structural (support) rolesLargely lost in leaf fall - must be replaced each year
Calcium Cycle
Calcium depletion occurring in many forests todayAcid deposition displaces soil calcium, logging removes itDecreased growth, higher mortality (more susceptible to pathogens)