Biota Flashcards
The conectedness food web
displays diet, who eats whom
not quantitative
the energy flow food web
additionally supplies information about the flux rates along the links in the web
how do you make a food web?
- stomach content analysis
- feeding trials (what eats what)(only cultured representatives)
- direct observation
- label with C13 or N15
What is biomass?
a pool (kg or mJ)
what is productivity?
a flux (in time units; kg/year)
interactions not included in food webs
mutualists, ecosystem engineers (earthworms) and litter decomposers
what is the problem with trophic levels
consumers often feed on multiple trophic levels
cannabalism
dont show energy flow
Architectural root traits
determine the spatial configuration of the entire root system of an individual plant.
commonly used traits include rooting depth, root length, density and root branching
influence carbon cycling (mainly inputs),
nutrient cycle plant uptake,
structural stability (erosion resistance and porosity, sometimes aggregation)
Morphological root traits
features of individual roots such as root diameter, specific root length, root tissue density and root dry mater content
mainly influences carbon cycling (inputs), nutrient cycling (plant uptake), structural stability (erosion resistance, porosity, aggregation)
Physiological root traits
characterise roots in terms of nutrient uptake, kinetics, root respiration, and release of root exudates
carbon cycling (inputs and decomposition (although unknown if exudates influence decomp.)) nutrient cycling (root n content affects inputs and mineralisation, exudates just inputs) structural stability (only exudates have influence on erosion resistance and aggregation)
Biotic root traits
involve direct interactions betweeen roots and soil biota that affect nutrient capture such as associations with Mycorrhizal fungi and rhizobia (in legumes) but also interactions with pathogens
carbon cycling (path. no influence on inputs, otherwise influence on inputs and decomp.) nutrient cycling (myco. no influencee on inputs and neutral on mineralisation, path negative influence on plant uptake. Otherwise others positive on inputs, mineralisation and plant uptake) structural stability (path no influence, myco no influence on porosity)
General properties of roots
high degree of plasticity
localised response to increased nutrient supply
e.g. increased root hairs when low P in soil; increasedd root hairs in localised places with high N
Lateral root initiation
lateral roots start growing out of casparian zone (under epidermis) this releases alot of exudates
Rhizodeposition consists of …
- Low molecular weight exudates
- Secretions
- Mucilages, sloughed off cells
percentage of allocated carbon lost by roots
respiration: 16-76%
Rhizodeposition: 4-70%
Low molecular weight exudates
- Compounds of low molecular weight which leak from all cells into the soil either directly or via intercellular spaces
- Examples are sugars, amino acids
- Exudation amount and composition can vary with a lot of factors (defoliation, water stress,…)
Secretions
- Includes both low and high molecular weight compounds released by metabolic processes
- Example: organic acids
chemical warfare
root - bacteria
positive interaction
PGPRs; symbionts
chemical warfare
root - fungi
positive interaction
->Biocontrol, VAM, endophytes
chemical warfare
root - root
positive interaction
growth facilitators
chemical warfare
root - nematode
positive interaction
chemical warfare
root - root
negative interaction
allelopathy
chemical warfare
root - nematodes (herbivors)
negative interaction
nematicidal/ insecticidal compounds
chemical warfare
root - fungi
negative interaction
->antifungal compounds
chemical warfare
root - bacteria
negative interaction
->antibacterial compounds, QS mimics
How can exudates even work?
theory 1. time lag in excretion of root exudates and arrival of microorganisms who “eat”/ decompose exudates (this also leads to spatial separation of initial excretion of exudates and microorganisms)
theory 2. transport of substances via a mycorrhizal fast lane
border cells role in defence (example)
“lure of the sirens”
one root tip “loses” boarder cells. Nematods swarm to root tip with boarder cells leaving tip without boarder cells nematode free
The rhizosphere
Among other factors, the release of Mucilages, mucigels, sloughed cells and tissues (plus dead roots) leads to the establishment of an important soil hot spot, the rhizosphere.
The rhizosphere
definition by Hiltner 1904
Soil region under immediate influence of plant roots and in which there is a microbial population distinct from the rest of the (bulk) soil.
Mycorrhizal fungi
Mycorrhizae (singular: mycorrhiza) are highly evolved, generally mutualistic associations between soil fungi and plant roots (literally: fungus-root).
Mycorrhizal associations involve 3-way interactions between host plants, fungi (communities) and soil factors
Arbuscular-mycorrhizal fungi (AMF)
All fungi that form this association are in the phylum Glomeromycota (Schüßler et al. 2011). There are currently about 210 morphologically described species. The sequence data base is steadily increasing with environmental sequences (MaarjAM)
it is estimated that 2/3 of all plant species on earth form associations with AMF
AMF structures
Arbuscules- in cells, dont alter cell structure (look like trees), responsible for nutrient exchange
Vesicles- only some AMF’s produce vesicles, used for storage
Spores- asexual reproduction
Hyphae
plant level function of AMF
Nutrient uptake (P, also N; micronutrients)
pathogen protection
Effects on biomass, to some extent nutrient content, very well documented
Less well known: early life history stage effects!
community level function of AMF
Influence on community structure (influence on rare or dominant plant species)
ecosystem level function of AMF
Soil aggregation, soil C storage
Nutrient cycling processes
Leaching, nutrient losses
Ectomycorrhiza ECM
Mostly Basidiomycota, a few Ascomycota; fairly large diversity (about 5,000 described)
evolutionarily much younger than Glomeromycota. Communities often species-rich (>200 morphotypes)
An estimated 2,000 plant species (Gymnosperms and Angiosperms) form this association, including Pinaceae, Fagaceae, Betulaceae. Few tropical trees.
ECM structures
mantle- covers the root, substantial modification of root morphology
Harting net- characteristic for ECM. hyphae do not grom intracellularly. (Grow in root but not in cell)
Rhizomorphs- thread or cord like structure made up of multiple hyphae in soil
fruiting bodies- can be formed above and below ground, not 1:1 relationship between fruiting bodies and ECM on roots.
Pathogenic root inhabiting fungi
a pathogent is an agent, biotic or abiotic, that causes disease by interfering with one or more of the essential functions of the plant
Parasitic root inhabiting fungi
important destinction between obligate and facultative parasites.
Facultative can use food (nutrients) from other sources when they do not parasitize. They are sacrotrophic.
Plant disease
disease triangle
what is “needed” for plants to get diseased
Pathogen - presence, virulence, abundance etc.
Environment - conditions favouring disease
Host - presence and degree of susceptibility
Amount of crops lost to fungi
Rice blast - 10-35%
Stem rust (wheat) - 10-70%
Corn smut - 2-20%
Late blight (potato) - 5-78%
soybean rust - 10-80%
Fusarium
genus with mostly harmless species but some extreme plant pathogens
e.g. fusarium wilt
Pythium
damping off disease of seedlings ( rotten apearance at soil interface)
can also be of importance without catastrophic epidemics.
e.g. black cherry seedlings are “killed” close to mother tree when in high density to avoid competition