Download Plant 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
NPP dry metric tons/ha/yr
Carbon Cycle
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, 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
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)