Soil Organisms in the Polar Regions
Soil is the most biologically rich medium on the planet. Untold
numbers of organisms, such as beetles, springtails, mites, worms,
spiders, ants, nematodes, fungi and bacteria, interact with one
another and with plants to form a web of biological activity. Soil
biodiversity is the term used to describe this diversity of life, both
in terms of quantity and variety [21,22].
NEMATODES:
root-feeders
ARTHROPODS:
shredders
ARTHROPODS:
predators
PLANTS:
shoots and roots
BIRDS
The nature of soil biodiversity
Soil biodiversity is conventionally used in a genetic sense and denotes
the number of distinct species (richness) and their proportional
abundance (evenness) present in a system, but may be extended to
encompass phenotypic (expressed), functional, structural or trophic
diversity. The total below-ground biomass generally equals or
exceeds that above-ground, whilst the biodiversity in the soil always
exceeds that on the associated surface by orders of magnitude,
particularly at the microbial scale.
Ecosystem services from soil biota
The soil biota plays many fundamental services in delivering key
ecosystem goods and services, and is both directly and indirectly
responsible for carrying out many important functions.
•driving nutrient cycling
FUNGI:
mycorrhizal fungi
saprophytic fungi
ORGANIC MATTER:
water, residue and
metabolites from
plants, animals and
microbes.
1st TROPHIC LEVEL:
photosynthesizers
BACTERIA
2nd TROPHIC LEVEL:
decomposers
mutualists
pthogens, parasites
root-feeders
NEMATODES:
predators
PROTOZOA:
amoebae, flagellates
and ciliates
3rd TROPHIC LEVEL:
shredders
predators
grazers
4th TROPHIC LEVEL:
higer level
predators
MAMMALS
5th and higher TROPHIC LEVELS:
higer level
predators
The soil food web: relationships between plants, dead organic matter,
soil fauna, and soil microorganisms (adapted from USDA [23])
•regulation of water flow and storage
•regulation of soil and sediment movement
Key functions performed by
soil biota
•regulation of other biota (including pests and diseases)
•detoxification of xenobiotics and pollutants
•Primary production [plants, cyanobacteria, algae
•regulation of atmospheric composition.
•Secondary production [herbivores]
•Primary decomposition [bacteria, archaea, fungi, some fauna]
Consequences of soil biodiversity
•Secondary decomposition [some soil microorganisms, protozoa,
nematodes, worms, insects, arachnids, molluscs]
The relationships between biodiversity and biota functions are
complex and somewhat poorly understood, even in aboveground situations. The exceptional complexity of below-ground
communities further confounds our understanding of soil systems.
Three important relationships between biodiversity and biotic
functions are:
Repertoire: for a biologically-mediated process to occur,
organisms that carry out that process must be present;
Interactions: most soil organisms have the capacity to directly or
indirectly influence other organisms, either positively or negatively;
Redundancy: the more organisms there are that can carry out
a function in a particular soil, the more likely it is that if some are
incapacitated or removed the process will remain unaffected; those
that remain fill the gap.
There is evidence that soil biotic communities are coupled to their
associated vegetation, such that there is a mutual dependence
between above-ground and below-ground communities, and hence
that compromised soil communities may curtail particular plant
assemblages from forming.
•Soil structural dynamics [bacteria, fungi, cyanobacteria; algae,
worms, insects, mammals]
•Suppression of pests and diseases [bacteria, actinomycetes, fungi,
protozoa, nematodes, insects]
•Symbioses [bacteria, actinomycetes, fungi (notably mycorrhizae) ]
•Soil organic matter formation, stabilisation and C sequestration
[virtually all groups, directly or indirectly]
Soil contains a huge variety of life ranging from soil
microorganisms, worms and insects to mammals. This picture
illustrates the diversity within soil mites (DW).
•Atmospheric gas dynamics, including generation and sequestration
of greenhouse gases [bacteria for nitrous oxides, methane; all biota
for CO2]
•Soil formation [bacteria, fungi]
Threats to soil biodiversity
A healthy soil biota needs an appropriate habitat. Soil provides the
space (e.g. the complex pore network) that contains the necessary
water, air and nutrients to support life under ground. Hence threats to
soil such as erosion, decline of organic matter content, contamination
and urbanisation all serve to put pressure on soil biodiversity by
compromising or destroying the habitat of the soil biota.
Collembola (springtails) are part of the soil mesofauna. (OE)
Consequences of decline in soil biodiversity
From a functional perspective, species richness is of little
consequence. Rather it is the functional repertoire of the soil
biota that is critical. For processes such as decomposition, there
is evidence of a high degree of redundancy at a microbial level.
Processes such as nitrification (the oxidation of ammonium)
are carried out by a narrower range of bacteria and there is less
redundancy in this group. For highly specific symbiotic associations,
such as those between dwarf shrubs and certain mycorrhizal fungi,
there is total dependence and hence zero redundancy.
Reduced biodiversity will have differing consequences in relation to
different soil processes. Experiments have shown that below certain
thresholds of soil biodiversity, some very specific soil processes are
impaired compared to natural systems. Given our limited state of
understanding of the consequences of soil biodiversity, it is common
sense that a strong precautionary principle needs to be applied.
A protozoe, an organism with only one cell, between fungal
hyphae. Usually protozoa and fungi are invisible to the naked
eye. They play an essential role in decomposition of organic
matter and nutrient cycling. (OE)
Soil biodiversity and climate change
Lemmings (Lemmus lemmus) are small burrowing rodents that are common
in the Arctic. Lemmings do not hibernate during the winter instead they
burrow through the snow to find food stored in advance. The myth that
lemmings commit mass suicide when they migrate is not true! (SN)
Low soil temperature and water deficit in some soils are important
constraints for biological activity in the circumpolar region.
Therefore, climate change in terms of warmer and moister
conditions will support the accumulation of organic matter in soils
(e.g., humus formation) that create habitats which are better suited
to biotic activity than exist at the present. This change will lead to
an increase of soil biodiversity by the appearance of thermophilic
organisms (creatures that prefer warmer habitats). An increase in
soil biodiversity can seriously alter how a soil functions. In previously
frozen ground, melting permafrost will lead to waterlogging in poorly
drained soils. Deep peat formation will be stimulated in these soils.
In drier conditions, humus formation can be expected.
Soils in Northern Latitudes | Soil Atlas of the Northern Circumpolar Region
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