Lecture 8 CM Flashcards
Soil is created by the interaction of
physical and chemical
weathering of rock; sedimentation; climate and living organisms
Overall soil fertility is influenced by
physical, chemical and biological components
Soil nutrient cycling and availability are controlled by
bacteria, which are influenced by soil pH, aeration, temperature and nutrient balance
After climate, soil fertility is
the most important factor in controlling ecosystem NPP, and in determining the sustainability of local agricultural systems
After temperature and rainfall, ___ has greatest impact on Biome structure
Soil
Important aspects of soils that determine biome and habitat productivity:
Physical component
• Inorganic component
Organic component
Physical component
Physical component
(f. of structural and chemical properties, water, temperature)
• Inorganic component
• Inorganic component
(f. bedrock, weathering and siltation)
• Organic component
• Organic component
(f. OM, soil microbes, protists, fungi, animals, plants)
The productivity of a given over-ground habitat is dependent on the
functioning and efficiency of the organic component of the soil, particularly the microbes
The soil is a very complex,
The soil is a very complex, 3-dimensional ecosystem with highly diverse microbial and invertebrate communities
biological activity and nutrient cycling is concentrated in
the uppermost layer
Soil Profile: horizons, biota & nutrient cycling
Humus - Decaying Organic Matter [OM] Topsoil - Humus OM/ mineral/ clay mix Leached layer - sand and silt
Subsoil - clay + leached minerals Regolith - bedrock, rocks + some clay
A Typical Soil Profile
OM
Humus/ Topsoil
Leached layer, low mineral content
Subsoil rich in oxidised-metals that have been leached from above
In general, soil profile is consistent across different habitat types, with
nutrients and microbes bound up with organic matter in the upper layers, and nutrient-poor leached layers underneath
Soils develop over time in conjunction with
bedrock weathering and biological activity
In each habitat, soil develops over time as
bedrock weathers and biological activity increases
Most often, soil forms around
fragments of the bedrock directly below, other times, glacial or river sediment dominates
The amount of soil biological activity is influenced by
abiotic factors and the soil biota
A mix of organic and inorganic components determine
the fertility of soils
• Inorganic component:
alumina-silicates (containing Mg, K, Na, Fe, Ca etc. in compounds); silica; calcium carbonate
• Organic component:
: raw decomposing material; colloidal humus
Soils comprise a continuum of organic types, ranging from
from the most fertile
(called ‘Mull’) to the least fertile (called ‘Mor’)
Mull organic matter:
- characteristic of fertile soils
- good aeration and temperature
- cycling of organic material is rapid
- microbes and soil animals abundant
Mor organic matter:
- forms in less favourable condition (base-poor rocks or in waterlogged soils) - OM accumulates and acidifies (leaching)
- few decomposers, no nitrifying bacteria
Soil drainage characteristics vary according sediment composition
Poor drainage can alter soil chemistry by increasing waterlogging, decreasing aeration and pH.
Soils with good drainage have the
capacity to be well-aerated, with neutral to alkaline pH [depending on bedrock geology and type of sediment]
The most fertile soils are generally those with
good drainage, over base-rich bedrock
In Ireland these factors commonly
overlap in the East and Southeast
Soil pH has a major impact on soil fertility and ecosystem biodiversity
Nutrient availability decreases with increasing soil acidity (lower pH)
• This directly impacts the ability of plants to source essential nutrients for growth and reproduction
• The impact of soil acidity can be seen in the Arctic Tundra of Alaska, for example, where fewer Plant Species survive in low pH soils compared to neutral soils (after Gough et al, 2000)
The Soil Biota comprises several different groups of organisms:
Bacteria, fungi and earthworms have greatest impact on soil health
See slide
Soil Bacteria
Pseudomonas (free-living and rhizophilous Bacteria)
Actinomycetes (Filamentous Bacteria)
Nitrifying bacteria (oxidise ammonia to nitrite and nitrate)
Soil Fungi
Fungi - root mycorrhizae (symbionts)
Fungi -opportunistic saprotrophs
Soil Protozoa
Motile protists (bacteria eaters), eg. Amoebae, Flagellates, Ciliata
Soil Invertebrates – soft bodied
Nematodes (herbivores, detrivores and predators)
Earthworms (detrivores e.g. Lumbricus terrestris)
Soil Invertebrates – exoskeleton
Beetle (Coleoptera) and Fly (Diptera) Larvae, can be detrivores, omnivores or carnivores
Collembola or Springtails (Detrivores) Along with earthworms & nematodes are the most numerous invertebrates
Woodlice (Crustacea) Detrivores
The breakdown of soil organic matter involves many organisms
See slide
Decomposition and nutrient cycling in soils are impacted by both temperature and water content
Relative soil microbial respiration rate, a measure of the overall biological activity of the soil, is significantly impacted by water content and temperature.
