Habitat Flashcards
The every day life definition (Webster’s New Collegiate Dictionary)
“The upper layer of earth which can be dug or plowed and in which plants grow”
This is the engineering definition of soil (Spangler and Handy, 1982)
“All the fragmented mineral material at or near the surface of the earth, the moon, or other planetary body, plus the air, water, organic matter, and other substances which may be included therein”
This geological definition of soil introduces the idea of alteration in place as a distinction between soil and sediment. (Nature 391, 12, 1998)
“Material altered in place at the surface of a planetary body by physical, chemical or biological means.”
Soil science definition (Buckman and Brady, 1970, The Nature and Properties of Soils)
Emphasizes the strong two-way interactions between biota and the soil habitat (Coleman & Crossley, 1996, Soil Ecology)
“A natural body, synthesized in profile form from a variable mixture of broken and weathered minerals and decaying organic matter, which covers the earth in a thin layer and which supplies, when containing the proper amounts of air and water, mechanical support and, in part, sustenance for plants”
“…with its living organisms…”
The pedosphere
the envelope of Earth where soils occur and soil forming factors are active
Where does the pedosphere develop?
where there is a close interaction between the atmosphere (soil air), biosphere(litter and organisms), hydrosphere (soil water), and lithosphere (soil and minerals)
Soil formation
stage 1
- Bedrock is weathered into parental material (unconsolidated rock fragments)
- Parent material can stay in one place or be transported by gravity, water, wind, glaciers
soil formation
stage 2
initial horizons are formed by additions, removals, mixing and transformations
(mixing can be done by worms)
soil formation
stage 3
mature soil is formed by further differentiation of soil horizons
Soils are dynamic bodies (function of time t) that respond to variety of soil forming factors (Jenny 1941):
S = (climate, parent material, biota, topography, vegetation)t + human (t2)
what does it mean that soil responds to a variety of factors?
that there is a considerable diversity within soils
Variability and complexity of soils
- large variation of soil types across globe
- depth of where bedrock starts increases from arctic to tropical climate (equator)
soil taxonomy
- 12 orders
- inceptisoil makes up 17%, most common soil type
A pedon
minimum of 3 dimensions of a soil that are necessary to describe it
In which layer are the most microbes?
…
Horizontal soil variability (small scale)
dependnet on pH, Carbon
What serious problem is there with the measurement of temporal patterns in soil ecology?
What examples can you think of, on what time scales?
???
“typical soil” percentage of dry weight
93% mineral
7% organic matter
organic portion of soil dry weight
85% dead
10% plant roots
5% Edaphon
soil biota percentage dry weight
40% Bacteria & Actinomycetes 40% Algae & Fungi 12% Earthworms 5% other macrofauna 3% mesofauna
sand
2mm-50µm
11-227 cm^3/g
silt
50µm-2µm
454 cm^3/g
clay
<2µm
8,000,000 cm^3/g
(can be a size fraction, a texture class name or/and a class of minerals)
loam
perfect mixture of sand silt and clay
soil organic matter
- relatively small and dynamic
- Of multiple origins (plant, animal, microbe)
- Incredibly chemically complex
- Almost impossible to satisfactorily characterize chemically
The ecosystem perspective on the importance of soil organic matter
- carbon repository
- roughly two thirds of all terrestrial carbon contained in soil organic matter
The soil fertility/ soil science perspective on the importance of soil organic matter
- cation exchange capacity
- aggregation
the soil microbial perspective on the importance of soil organic matter
- source of carbon (for heterotrophs)
- source of nutrients
- A microbial product
fractionation methods
SOM is described based on physical and biochemical differences of compounds
- solubility
- Density (polytungstate)
- Size
- Charge
Fulvic acid
soluble in acid
soluble in alkali
Humic acid
isoluble in acid
soluble in alkali
Humin
insoluble in acid
insoluble in alkali
Non-humic substances
- Recognizable plant debris (this can be separated out as a separate class of SOM, the detritus)
- All of the identifiable classes of organic compounds (such as carbohydrates and peptides)
Humic substances (Huminstoffe: Fulvinsäuren (oder Fulvo-), Huminsäuren, Humine)
- The remaining amorphous, highly transformed, darkly colored material.
- Cannot be identified as belonging to an established group of chemical compounds
deffinition of humic substances stevenson 1985 (traditional)
Large, multifunctional polymers which are bound to mineral surfaces via a broad range of bonding mechanisms
definition of humic substances piccolo 2001 (zonal layer model)
small molecules with dynamic interactions
- contact zone
- zone of hydrophobic interactions
- kinetic zone (outer region)
Other organic components: carbonized materials
Carbonized material can either be present in soil because of
• (natural) fires (incomplete combustion),
• or because it has been added as a soil amendment
Biochar
- charcoal primarily made out of biomass for the purpose of enhancing soil carbon sequestration. Modeled after terra preta soils in the Amazon basin.
- Two different sources of biochar: pyrolysis (high temperatures, low oxygen) or hydrothermal carbonization (aqueous, milder conditions)
Multiple (often positive) effects of carbonized materials
- soil physico-chemical properties
- soil biota (Lehmann et al. 2012 SBB; Thies, Rillig & Graber 2015),
- plant growth
Soil structure:
The combination or arrangement of primary soil particles into secondary particles, units or peds.
Ped:
A unit of soil structure, such as an aggregate, formed by natural processes.
Clod:
A compact, coherent mass of soil produced artificially, usually by such human activities as plowing and digging (especially when soils are wet).
Aggregates
Aggregates are (with few exceptions) hierarchically structured combinations of primary particles.
Aggregates
2000µm
solids with ores
Aggregates
200µm
binding agent: roots and hyphae
Aggregates
20µm
binding agent: plant and fungal debris encrusted with inorganics
Aggregates
2µm
binding agents: microbial and fungal debris encrusted with inorganics
Aggregates
0.2µm
Amorphus alluminosilicates, oxides and organic polymers sorbed on clay surfaces and electrostatic bonding, flocculation
AMF on soil aggregates
biological effects I: AMF influence microbial communities
Biological effects II: Fungal interactions with the soil food webs
Biochemical effects: release f mycelium products (glomalin etc.) from decomposing or living hyphae
Physical effects I: Hyphal enmeshment of particles/ microaggregates; altered water regime (dry wet cycle)
Physical effects II: alleigment of particles, exerting pressure
macropores
>0.08mm
Allow ready movement of air and water.
• Large enough to accommodate roots and microarthropods.
• Different types
-Packing pores (spaces left between primary soil particles)
-Interped pores (spaces in between peds)
-Biopores (formed by biota; often tubular, formed by roots)
micropores
<0.08mm
- Too small to permit much air movement
- Usually filled with water; water movement slow
- Larger ones accommodate plant root hairs or microorganisms; small ones may be even to small for bacteria
what is the difference between soil air and the atmosphere
- soil air is almost always saturated with water vapor
- soil air slightly higher CO2 and N2
gravitational water
all water that drains out of the soil
field capacity
water is held in the capillary pores, macropores have air
wilting point
water unavailable to plants
why do plants wilt when the relative humidity in soil is still 0.9926?
Because the water is unavailable to plants. The water is in thin biofilms around aggregate.
The water potential is to low for plants to use the water (-15 bar)
is the soil atmosphere the same everywhere?
- higher concentration of CO2 near roots (respiration)
- center of aggregates anaerobic
- diffusion limiting factor
why can fungi grow at the lowest water potentials?
- they increase the concentration of solutes within cell so that water doesnt leave but rather is taken in. water always flows from high to low water potential
- they have compatible solutes that do not interfere with cell processes
Different amount of work needed to remove fractions of soil water
- Adhesion of water to the soil solids (matrix) provides a matric force: reduces the energy state of water
- Attraction of water to ions and other solutes results in osmotic forces, also lowering the energy state of water.
- Gravity pulls water downward (energy level of water higher up in the soil profile is higher than further down)
- Kinetic energy usually negligible
- Soil water potential is the difference in energy levels between pure standard water and the soil water.
Gravimetric method
- Measuring soil water content
- weighing soil and knowing dry weight
Neutron scattering (probe) Measuring soil water content
- Fast neutrons are emitted
- When fast neutrons encounter hydrogen atoms (like in water), they get slowed down and scattered
- Slow neutrons are counted with a detector
- Need access hole
Time-domain reflectometry (TDR)
Measuring soil water content
- Measures the time (picoseconds; 10-12 sec) it takes for an electromagnetic impulse to travel along two buried metal rods;
- The transmission time is dependent on the dielectric constant of the medium (soil) in which the waveguides are buried.
- Relatively expensive; small sensing volume
FDR Frequency-domain reflectometry
Measuring soil water content
- changes in soil moisture are detected by changes in circuit operating frequency
- advantage: cheap (relatively!)
- like TDR, small sensing volume
Tensiometers
Measuring soil water potentials (Saugspannung)
- Water-filled tube with a porous ceramic cup at the bottom, and at the top an air-tight seal (Keramik-Kerze);
- Vacuum develops and is measured with a pressure gauge as water leaves the tensiometer at the bottom
Thermocouple psychrometry
Measuring soil water potentials (Saugspannung)
- Water potential of the liquid phase of a soil is inferred from measurements within the vapor phase in equilibrium with the liquid phase
- Water potential is directly related to relative humidity
- Relative humidity is measured extremely accurately (why is that necessary?)
- This is done by actually measuring a temperature decrease due to evaporation of a water droplet (which is formed by condensation in the first place by cooling down the thermocouple); evaporation is proportional to humidity
