biosphere Flashcards
soil organisms
‘biological engine of the earth’, drive and modulate key processes in soil
attributes of soil organisms that support high soil biodiversity
- fast growth rates and high dispersal rate
- horizontal gene transfer
- dormancy
Kaolinite
lower surface area
Montmorillonite
higher surface area
tree of life
a taxonomic approach to diversity revealing dominance of bacterial genetic diversification
classification of soil biota by size
microflora and microfauna
photoautotroph
energy source: light
carbon source: carbon dioxide
photoheterotroph
energy source: light
carbon source: organic compounds
chemoautotrophs
energy source: chemical compounds
carbon source: carbon dioxide
chemoheterotrophs
energy source: chemical compounds
carbon source: organic compounds
what are microbes made up of?
70-85% water
50% protein (dry mass)
what do microbes need to grow
- favorable environment
- water
- mineral nutrients
- energy sources
- election donors and acceptors
Biomass C:N
8-12 bacteria
biomass C:N (fungi?)
30 fungi
bacteria’s traits that define a microbes ‘nice space’
- cell wall
- morphology
- metabolism
- oxygen requirements
- plasticity
- substrate preferences
obligate aerobe
oxygen is required
facultative anaerobe
oxygen is preferred, but not required
obligate anaerobe
oxygen is toxic, TEA required
microbes make extracellular enzymes to…
break down organic compounds so they can assimilate them
mycorrhiza
- symbiosis between a fungus and a plant (root)
- one of the oldest symbiotic relationships
key attributes of fungi
- heterotrophs
- key players in decomposition
- multicellular
- fungal spores develop from hyphae
- cell walls made of chitin
- prefer slightly acidic soils
- sensitive to disturbance
fungal hyphae
- thin filaments making up the fungus
- grow at the tips and branch out
Mycelium
mass of hyphae
wood rot fungi
primary decomposers of complex structural organic matter like lignin
bacterial growth rate…as pH increases
increases
fungal growth rate…as pH increases
decreases
Alfalfa
rich in nitrogen (C:N<20)
Straw
less available N, good for fungal growth
soil fauna regulate what microbial processes
- Comminution
- translocation
- inoculation
- predation
comminution
fragmentation of material (jump start microbial decomposition)
translocation
movement of materials
inoculation
movement of microbes
predation
grazing on microbes
Bioturbation
mixing and rearrangement of the soil
Dormancy/resting states have been linked with..
maintenance of biodiversity
microfauna
- <100 micromm, predators of microorganisms
- diverse set of feeding preferences
nematodes
- soil microfauna
- occupy multiple trophic levels
- feed on plant roots, bacteria, and fungi
- aquatic
Mesofauna
- 100-200micromm
- soil predators
- pathogens
- herbivores
major functions of mesofauna
- regulations of bacterial, fungal and microfaunal populations
- nutrient cycling
- transport of materials
- alter litter decomposition rate
- contribute to soil development
- bicontrol agents
macrofauna
- > 2mm
- soil predators
- herbivores
- ecosystem engineers
rhizosphere
the zone of the root’s influence on the soil
why do food webs matter
- provide info about species richness, population sizes, resource niches, and how species’ populations are regulated
- estimate the amount of C and N mineralization facilitated by different
- understand how a change in a food resource will alter energy flows and nutrient availability
predator C:N
> 1 nitrogen mobilization
resource C:N
<1 nitrogen immobilization
does fear increase or decrease nitrogen content
decrease
AMF (arbuscular mycorrhizae)
- grows inside plant cells
- spores are located outside
- inorganic nitrogen but mostly P
- obligate symbionts
EMF (ectomycorrhiza)
- grows in between plant cells
- do not penetrate cells like AMF
- fruiting bodies
- larger hyphen network compared to AMF
mycorrhizae
-contribute to soil C storage
Herbivory
consumption/removal of plant tissue
below ground impacts of herbivory
- changes plant productivity and C allocation
- changes resource quality
- soil physical properties
negative feedback
slows down or diminishes a system process. Tends to stabilize a system
positive feedback
increases a system process. Tends to drive the system to a new state
herbivory can be positive or negative depending on…
- site
- herbivores
- plant community
herbivory, grazing effect
- can be good for grasslands, reinforcing fertility and plant productivity
- plant community succession slows
SOM (soil organic matter)
foundation of ecosystem productivity, soil quality, agricultural sustainability
SOM consists of:
- plant residues at various stages of decay
- soil microbes, fauna, and their by-products
Primary SOM constituents
- proteins, amino acids, nucleic acids
- carbohydrates
- phenolics
- lignin
how root inputs persist
- chemical recalcitrance
- physical protection
- physio-chemical protection
how does litter decomposition happen?
- physical fragmentation
- leaching of soluble compounds
- chemical transformation/enzymatic breakdown
process of decomposition
- fragmentation
- further fragmentation
- extracellular enzymes of biological origin, complex polymers
- extracellular enzymes, producing monomeric units
factors affecting SOM levels
- climate
- vegetation
- land use
- climate change
physical protection
inaccessibility to decomposition
chemical-physic protection
-mostly based on binding mechanisms between SOM and minerals
SOM = ….
inputs - outputs
SOM inputs:
plant productivity
SOM outputs:
mineralization
SOM pools
- active, labile, fast cycle, biologically available
- free or within aggregates
- held tightly onto clay minerals and metal oxides
pool 1 function
energy, nutrients for plants and microbes
pool 2 function
soil structure, nutrients
pool 3 function
C sequestration
least protected mechanism for SOM accumulation
chemical recalcitrance and abiotic constraints
most protected mechanism for SOM accumulation
chemical/physio protection
how to enhance SOM levels
- add continuous supply of high quality organic matter
- add legumes to crop rotation
- reduce tillage when feasible
- use perennial vegetation when feasible
- maximize plant growth
N cycle
- mineralization
- nitrification
- denitrification
- leaching
- N2 fixation
Nitrogen
a scarce resource that often limits primary productivity in many ecosystems
nitrogen cascade
undergoes many different transformations, changing from one form to another as organisms use it for growth and energy
Reactive N is linked to…
multiple ecosystem and human health issues
Mineralization
- organic Nitrogen to NH4 (ammonium)
- can sometimes turn in to nitrification if converted to NO3
Nitrification
- ammonium–>NO2 (nitrite)–>NO3 (nitrate)
- aerobic process
Denitrification
- conversion to gaseous N
- if not completed, N2O is the product which is potent
- anaerobic process
- returns inorganic nitrogen to the atmosphere
N2 fixation
- atmospheric N2–>NH4
- nitrogenase is the enzyme that catalyzes the reduction of N2 to NH3
assimilation
- uptake of inorganic N into organic biomass
- can be microbial, soil biota, or plant assimilation
controls on soil N concentrations depend on what two processes?
mineralization and assimilation rates
controls on soil N concentrations
- inorganic N
- immobilization
- organic N
- mineralization
BNF
biological nitrogen fixation
controls and limitations on N fixation rates
- physiological
- soil properties
- ecological
- energy and nutrient constraints
nitrogen pools
- ammonium
- nitrate
- nitrite
some global change factors
- increased drought
- increased precipitation
- warmer temperatures (one of the biggest factors)
- erosion
Why is canada warming faster than other places?
- loss of snow and sea ice, so less reflection and more retention of heat
- larger surface warming
Albedo
- indicated how well a surface reflects solar energy
- the more a surface absorbs heat, the lower the number value of Albedo
what is predicted on precipitation in canada?
- winter precipitation expected to increase and more so in the north
- summer precipitation expected to decrease
