Soil Habitat Flashcards
Soil formation
Dependent on climate, organisms, parent material, relief and time
Weathering of exposed rock and degradation leads to formation; minerals converted into simple molecules and ions
Initial stage: thin litter later, first organisms colonise surface and speed weathering; basic plants (mosses, liverworts, lichens) w rhizomes to remove nutrients from rock; form protosoil
Advanced: thicker litter layer; plants adapted to stress w actual deeper roots (sedges, grasses and shrubs); developing soil layer
Later: Larger species (forests) w deep roots; brown forest soil and altered parent material
Rock Cycle
New erupted magma crystalises at surface (igneous)
Igeous exposed and weather (sedimetary) or heated and under pressure (metamorphic)
Sedimentary moves deeper and heated and under pressure (metamorphic) or melts (igneous)
Metamorphic melts (igneous or magma) or exposed and weathers (sedimentary)
Weathering changes rock chemistry - sediments formed at rind, inner layer of core
Soil horizons
Litter
O horizon - organic, humus
A horizon - surface soil, accumulation of org matter as it leaches, minerals and humus
B horizon - sub soil, deepest roots can go, deposited minerals, metals and salts, little org material
C horizon - substratum, partially weathered parent material
R horizon - bedrock, unweathered material
Aggregate size and texture
Gravel
Sand - little water retention, easy for roots, drought susceptible, easy to work
Silt
Clay - holds water, hard for roots, heavy soil so hard to work
Minerals
Solid chemical compounds w defined chemical composition and specific chemical structure
Silicates: silicon tetrahedra (4 O connected to 1 Si); silicon tetrahedrom wants to bind w cations to form neutral crystal
Inosilicates: unsatisfied valencies so needs to connect to bigger structure; pyroxene - simple chain; amphibole - 2 interlocking simple chain
Phyllosilicates: sheets of single layers of linked tetrahedra or octahedra; or 3D covalently bonded combinations
Clay mineral: silicate tetrahedral sheet + metal hydroxide octahedral sheet
Mineral structure
Sheets: combinations of planes of atoms
Layers: combination of sheets
Crystals: Stacks of sheets or layers; interlayer space
Soil composition
Mineral matter (40-60%)
Water (20-50%)
Air (10-25%)
Org matter (very little)
Org matter made up ofL
Fresh residue (10%) - plant debris and animal residues
Living org (<5%) - soil organisms, energy from oxidative decomposition
Humus (33-50%) - no longer decomposing material, stable org matter
Active fraction (33-50%) - actively decomposing org matter
Decomposition
Mineralisation: elements converted from complex org molecules into simple inorg components (broken down); release of CO2
Immobilisation: carbon that wasn’t converted to CO2 incorporated into microbes; mineralised N,P, S incorporated too; SOC enters mircobial pool
C immobilised further into humus, peat and fossils
Respiration of microbes releases C
Org C return to soils
Depends on:
Climate
Vegetation type
Land use - distubance by agriculture results in low rate of return
Timber fall hard to break down so less labile
Plant litter
Carbohydrates: rapidly decomposed, quickly enter org C pool
Proteins: broken down fast, metabolised into amino acids via proteolysis; incoporated into microbial biomass by immobilisation (high C and low N) or mineralisation (low C but high N)
Fats
Other compounds
Structural components hard to decompose: large polymers (energy and specific enzymes and many steps o decompose)
MC
Symbiotic relationship: nutrients to plant, carbon from plant
Precursor to roots
Can help primte plant immune systems for fungal attacks so can respond faster to actual disease 4
EMC
EMC: sheath around roots;
Signals between plant and fungi and production of MYC factors which diffuse across plant membrane to root
Branching induced in root so more chance for root and hyphae to make contact
Plant produces strigolactones which diffuse into soil to MC
Hypha forms appressorium to penetrate roots and forms arbuscules
Fungus penetrates plant cell wall
Plant detects fungus and recognises fungal MAMPS
MC pushes but doesn’t break membrane
MC releases fungal effectors to supress defences
Start of symbiosis
Interfacial apoplast: nutrients released into here through transporter protein and other protein transfers it into plamt cell; same in opposite direction for carbon
PGPR
Promote growth through:
Direct - outcompete harmful pathogens
Indirect - produce hormones to ward off pathogens, make nutrients available
AMF
Help PGPR interact w plants
Increases PGPR colonisation of root and priming of plant immune system
Quicker deposition of callose when primed following attack
Phase1: plant sends signal for symbionts
Phase2: Fungal colonisation; defences of host
Phase3: Defences off; cell wall defences primed
Phase4: bacteria enter; more defences on; plant immunises itself
