Transcript Model of the Mineral Nutrient Cycle developed by P.F. Gersmehl in 1976 • • • Soil is the top layer of the earth that is composed.

Model of the Mineral Nutrient Cycle
developed by P.F. Gersmehl in 1976
•
•
•
Soil is the top layer of the
earth that is composed of
disintegrated rock particles,
humus, water and air.
Litter is organic matter in
and on the soil, it includes
humus and leaf litter.
Biomass is the total mass of
living organisms, mainly
plant tissue, per unit area. It
is a store of energy and is
also known as standing
crop. It can be measured in
3 ways:
- dry weight (kg/metre
squared)
- ash weight
- calorific value per unit area
biomass
litter
Store of
nutrients
Transfer of
nutrients
The size of the circles and arrows is
proportional to the amount of nutrients
soil
a)
Taiga (northern coniferous forest)
Relatively low as
Little
ppt.
conifers form only
one layer, little under
growth, limited
species, small needles
Continual
supply of
litter
biomass
Large store
because of low
rate of
decomposition
due to cold temp.
High runoff after
snowmelt when
ground still
frozen
Trees take up
nutrients
litter
Slow
decomposition
due to cold &
thick cuticles
Some leaching
due to ppt.
soil
Small store of
nutrients due to
poor drainage and
soil formed from
glacial deposits
which have low
fertility
Slow chemical
weathering of parent
rock due to cold
b) Steppe & Prairie (mid-latitude continental grassland)
Little
ppt.
Litter store small
as no trees, grasses
die back quickly
into soil
High runoff as
soils saturated
High
supply of
litter, grasses
die back in
winter
biomass
Some plants store their
own nutrients in
rhizomes & roots so not
as many nutrients taken
up from soil
litter
High
decomposition
due to wet &
dry seasons &
bacteria
Low ppt means
less loss of nutrients
from leaching
Small store due to
climate, insufficient
moisture to support
trees & growing season
reduced to 6 months
by cold temps. Much of
biomass beneath surface
as rhizomes & roots
soil
Large store of
nutrients due to
good drainage
Weather encourages
chemical & physical
weathering releasing
nutrients to soil
c) Selvas (tropical rainforest)
High
ppt. all year
Tall, dense & rapid
growth of vegetation.
Several layers &
countless species.
Continual
supply of
litter
biomass
Small store because
of high rate of
decomposition
High runoff because
of lots of rain,
soil cannot absorb
it all
The many plant roots
take up vast
amounts of nutrients
L
Rapid decay
due to heat &
moisture, ideal
for bacterial
action
Rapid leaching
due to ppt
soil
Small store due to
leaching and soils
inherent infertility
Rapid chemical
weathering due to
heat & humidity