1. 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
soil
Store of
nutrients
Transfer of
nutrients
The size of the circles and arrows is
proportional to the amount of nutrients

2. Taiga (northern coniferous forest)
Relatively low as
conifers form only
one layer, little under
growth, limited
species, small needles
Little
ppt.
Continual
supply of
litter
biomass
Trees take up
nutrients
Large store
because of low
rate of
decomposition
due to cold temp.
litter
Small store of
nutrients due to
poor drainage and
soil formed from
glacial deposits
which have low
fertility
Slow
decomposition
due to cold &
thick cuticles
High runoff after
snowmelt when
ground still
frozen
soil
Some leaching
due to ppt.
Slow chemical
weathering of parent
rock due to cold

3. b) Steppe & Prairie (mid-latitude continental grassland)
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
High
supply of
litter, grasses
die back in
winter
Little
ppt.
biomass
Litter store small
as no trees, grasses
die back quickly
into soil
Some plants store their
own nutrients in
rhizomes & roots so not
as many nutrients taken
up from soil
litter
High runoff as
soils saturated
High
decomposition
due to wet &
dry seasons &
bacteria
soil
Large store of
nutrients due to
good drainage
Weather encourages
chemical & physical
weathering releasing
nutrients to soil
Low ppt means
less loss of nutrients
from leaching

4. c) Selvas (tropical rainforest)
Tall, dense & rapid
growth of vegetation.
Several layers &
countless species.
High
ppt. all year
Continual
supply of
litter
biomass
Small store because
of high rate of
decomposition
The many plant roots
take up vast
amounts of nutrients L
High runoff because
of lots of rain,
soil cannot absorb
it all
Rapid decay
due to heat &
moisture, ideal
for bacterial
action
Small store due to
leaching and soils
inherent infertility
soil
Rapid chemical
weathering due to
heat & humidity
Rapid leaching
due to ppt