Lecture 10 Flashcards
Arbuscular mycorrhiza importance
important in most ecosystems
-most grassland plants, many tropical rain forest trees, some temperate woodland trees
where do ectomycorrhiza form
most boreal forest trees, and many temperate forest species
Arbuscular mycorrhiza in crop plants
lots! (cereals, peas,onions)
NOT found in oilseed rape, cabbages, mustard, sugar beet and quinoa etc
mycorrhizal fungi and passing of carbon
~12% of the terrestrial C cycle passes from plants to mycorrhiza
Arbuscular mycorrhiza hyphal lengths
10-100X long than roots
- in cereal crops typically rand 2-8m/g soil
- permanent grasslands 45-74 m/g soil many records
hyphae affect on soil
- effect microbiome of soil round roots (suppressing pathogens, supporting and eliciting plant growth promoting rhizobacteria)
- effect soil structure
primary function of mycorrhiza
- enhance ability to take up phosphorous
- esp Arbuscular mycorrhiza
- small hyphae diameter, as can enter pores in soil smaller than a root hair can
- exploit areas of nutrients
___ affinity P uptake in mycorrhizal compared to non-mycorrhizal plants of the same species
higher
which is faster: translocation down hyphae to roots (P H–> R C R–>H) or diffusion of P in solution
translocation down hyphae to roots (P H–> R C R–>H)
AM hyphae extend up to __ more than root hairs
up to 11cm or more
-allow to explore depletion zone (extend)
how do mycorrhizas increase P uptake by plants? evidence of use of organic P sources
Tarafdar & Marschner 1994
Jayachandan et al 1992
acid phosphatase activity is ___ around roots of mycorrhizal compared to non-mycorrhizal plants of the same species
higher
mycorrhizal saving fertiliser?
arbsucular mycorrhizal (cassava) grows in P deficient tropical soils
key to mycorrhizal success:
dependent on plant and fungal characteristics
-different species show diff responses to mycorrhiza
different plant species responses to mycorrhiza
costs & benefits are not shared equally between plants and are fungus specific
-some they don’t benefit some they do (some even suppress if they inhibit roots)
root length density effected by tillage?
No tillage increases root length particularly close to surface
cereal crops hyphae ____ km/ha to 10 cm depth
2 - 8 million KM
HUGE
ploughing’s effect on mycorrhizal infection in roots
just one occurrence of ploughing has a major negative impact, direct drilling is the only option to not effect it
hyphae & soil aggregation
hyphae play a role in holding water (glomalin protein) and aids in storing organic carbon
mycorrhiza always get greater yields?
not necessarily, ploughed and disc cultivated wheat + mycorrhiza yields don’t increase, do when directly drilled though (58% increase) using less fertiliser
how to gain highest corn yield work WITH nature not agains it =
the least energy requiring and highest yielding treatment =
- living clover clipped but not removed, no P fertiliser, no tillage
diversity of mycorrhizal fungi species effect on P uptake and hyphal length
both increase w increased diversity
hyphae growing inside plants =
induce systemic defences against shoot & root pathogens
-sooty mould of wheat
good mycorrhiza hosts
legumes as cover crop
what is “Round up”
glyphosate is a herbicide
-inhibits mycorrhiza spore germination
mycorrhiza & sunflower weeds
they help to suppress weed biomass, both in weed spp. that form mycorrhiza and those that do not
Agronomic practices: Favouring mycorrhiza
1) manure & compost
2) minimal tillage
3) low use of superphosphate fertiliser
4) mycorrhiza-compatible crops, cover crops and varieties
5) organic management
6) use of leys
agronomic practices: Impairing mycorrhiza
1) low organic matter inputs
2) repeated inversion tillage
3) high use of P fertilisers
4) varieties and crops with low or no capacity to form mycorrhiza
5) high use of weed killers and fungicides
6) continous cultivation
benefits of mycorrhiza, minimal tillage, growth of mycorrhiza-competent growth varieties, minimal use of agro-chemicals:
1) increase crop nutrient use efficiency
2) improved soil structure - macro aggregates that hold water, nutrients and organic matter and enable deep root growth
3) greater soil organic matter content of surface soil
4) increases populations of earthworms
5) improved soil drainage and micropore flows reducing risk of flooding and soil erosion
6) increased drought tolerance of crop
7) increased crop resistance to diseases and stimulation of plant growth rhizobacteria (PGPR)
8) suppression of weeds
