Plant Ecology Chapter 14 Ecosystem Processes Ecosystem Ecology

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 system Retention time - how long does it reside in a component

Ecosystem Ecology Pools, fluxes connected together into biogeochemical cycles Biology, geology, chemistry interconnected

Ecosystem Ecology Plants under the influence of some cycles, influence others Water, oxygen, carbon, nitrogen, phosphorus, sulfur, potassium

Water Cycle

Water Cycle 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

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 semiarid regions can reduce rainfall, increase soil temperatures, induce onset of desertification

Water Cycle Flux differences among, 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 infiltration PET>AET in dry climates PET=AET in intact tropical rain forests AET linked to productivity, decomposition

Carbon Cycle Primary productivity - rate of transfer of inorganic C from atmosphere into organic C in plants via photosynthesis

Carbon Cycle NPP dry metric tons/ha/yr

Productivity Different ecosystems related to leaf biomass Different forests - latitude, climate, elevation

Productivity

Estimating Productivity Standing biomass after a growing season Drawbacks: destructive, and ignores belowground productivity (can be majority in some plants)

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

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

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

Decomposition Dead stuff becomes soil organic matter, then via mineralization becomes inorganic nutrients, CO 2, water, and energy

Decomposition - Saprophytic fungi are the major decomposers of dead leaves, plant litter - Bacteria also essential, but only in latter stages

Decomposition Root decomposition of soft and hardwoods Decomposition largely an aerobic process - very slow in waterlogged, cold soils Physical, chemical characteristics also affect rate of decomposition

Net Ecosystem Production NEP is net accumulation of carbon per year by ecosystem Positive during growing season, negative during nongrowing season

Net Ecosystem Production Undisturbed ecosystems usually show small, positive accumulations of C each year Accumulation 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 cycle Needed by plants for chemical (growth, stress regulation), structural (support) roles Largely lost in leaf fall - must be replaced each year

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)