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)