Benefits to crop production from mycorrhiza Flashcards
Mycorrhizal fungi absorb nutrients from soil and pass these on to plants
The plants supply the fungi with sugar and lipid from photosynthesis - a mutual symbiosis
Hyphal lengths - typically 10-100x longer than roots
Leake et al, 2004
In permanent grasslands many records in the range 45-47meters per gram of soil
In cereal typical crops range 2-8 meters per gram of soil
Arbuscular mycorrhiza
Very important in most ecosystems:
Most grassland plants
Many tropical rain forest trees
Some temperate woodland trees
(angiosperms: ash, maple, sycamore, maple…
gymnosperms: giant redwoods, yew, juniper…
However- most boreal forest trees have ectomycorrhiza, as do many temperate forest species (angiosperms: beech, oak, birch, hazel…
gymnosperms: pine, spruce, larch, fir…)
Arbuscular mycorrhiza (AM)
Potentially important in most crops including:
Alliums: onions, garlic, leeks
Legumes: peas, beans, clovers, vetches etc.
Roots: potatoes, carrots, parsnips, cassava etc.
Cereals: maize, sorghum, barley, oats, wheat Cucurbits: Cucumber, courgette, marrow, pumpkin
Fruits: apples, oranges, banana, plums, pears, raspberries, strawberries, etc.
NOT found in
Brassicas: oilseed rape, cabbages, mustards, etc.
Amaranths: sugar beet, quinoa, etc.
How do we measure arbuscular mycorrhizal fungi?
Spores, microscopy, lipid markers and DNA
Use of the signature fatty acid 16:1w5 as a tool to determine the distribution of arbuscular mycorrhizal fungi in soil
Standard primers used for DNA identification of AM fungi do not detect Mucoromycotina.
Their importance has been hidden until recently.
First evidence of mutualism between ancient plant lineages (liverworts) and Mucoromycotina fungi (Field et al, 2018)
Average root length density
of 8 cm per cm3 of soil
= 120,000 km per ha to 15 cm depth under wheat. Agricultural topsoils typically weigh about 1.3 g per cm3
Root length = ~6 cm per g
The circumference of the Earth at the equator is 40,075km
AM hyphal lengths in soil:
Cereal crops 2–8 m g-1 soil
2,000,000 – 8,000,000 km ha-1 to 10 cm depth
Circumference of the Earth 40,075km
2 million ha of wheat in UK = mycorrhizal hyphae that would stretch from the earth to the sun 26,000 times or over 500 times to Pluto!
(Johansson et al., 2004)
SEE SLIDES (Lecture 10)
Significance of microbial interactions in the mycorrhizophere for sustainable agriculture
Extraction of P from pores in soil which are too small for plant roots or root hairs to access. There is increased effective volume of soil exploited by mycorrhizal plants:
Fine roots diameter 100 - 500 µm
Root hairs >10 µm
AM arterial hyphae 20-30 µm
AM feeder hyphae 2-7 µm
Translocation down hyphae to roots is faster than the rate of diffusion of P in solution.
Bieleski (1973) estimates 1000 x faster.
Higher affinity P uptake in mycorrhizal compared to non-mycorrhizal plants of the same species.
(Cress et al., 1979)
Marschner 1995
The role of mycorrhiza in plant P uptake and plant growth depends on plant and fungal characteristics
AM mycelia extend the width of the P depletion zone around roots
Do mycorrhizas increase P uptake from organic P by plants?
Use of some of the 95-99% of soil P which is unavailable to NM plants?
Evidence of use of organic P sources:
Jayachandan et al., (1992)
Tarafdar & Marschner (1994)
Potential fertilizer saving by AM- Cassava often grows in P deficient tropical soils
(Marschner 1995)
Mycorrhiza often synergistically operate with plant-growth promoting rhizobacteria
some bacteria involved in P solubilisation may help reduce the need to add P fertilisers. (Harris et al. 2006)
One-time tillage of no-till: effects on nutrients, mycorrhizae and phosphorus uptake
Garcia et al 2007
tillage reduced AM colonisation
Conventional ploughing and disking disrupts AM fungal networks and reduces P uptake
Kabir et al 1998
Soil aggregation and carbon sequestration are tightly correlated with the abundance of arbuscular mycorrhizal fungi: results from long-term field experimnts
Wilson et al 2009
Water-stable micro-aggregates increase with AM
Mycorrhizal fungi increase the energy required to break down soil aggregates
macroaggregates> 2mm
3 year grass-clover ley after continuous arable –rebuilds mycorrhiza activity and boots wheat growth
pasture > 3 year ley > Arable
for shoot biomass, root biomass and arbuscule abundance (in general)
AM – the costs and benefits are not shared equally between plants and are fungus specific
Van der Heijden et al 1998
Mycorrhizal – but unresponsive Mycorrhizal responsive Non-mycorrhizal
Plant species differ in their abilities to assist aggregate formation
Macro-aggregate stability is increased by hyphae (and possibly a hydrophobic glycoprotein glomalin)
(Rillig et al., 2002)
LOOK AT SLIDES 34
TO 51
leys and AM and legumes
Mycorrhiza-induced resistance: more than the sum of its parts?
Cameron et al
Mycorrhiza helps sunflower to suppress weed biomass-
both in weed species that form mycorrhiza and those that do not.
Agronomic practices
Favouring mycorrhiza
Manure and
compost
Minimal tillage
Low use of superphosphate fertilizer
Mycorrhiza-compatible crops, cover crops, and varieties.
Organic management
Use of leys
Impairing mycorrhiza
Low organic matter inputs
Repeated inversion tillage
High use of P fertilizers
Varieties and crops with low or no capacity to form mycorrhiza
High use of weed killers, and fungicides
Continuous cultivation
Potential benefits to crop production and soil quality of cropping systems that favour mycorrhiza (minimal tillage, growth of mycorrhiza-competent crop varieties, minimal use of agro-chemicals)
Increased crop nutrient use efficiency
Improved soil structure- macroaggregates that hold water, nutrients and organic matter and enable deep root growth
Greater soil organic matter content of surface soil
Increased populations of earthworms
Improved soil drainage and macropore flows reducing risk of flooding and soil erosion
Increased drought tolerance of crop
Increased crop resistance to diseases and stimulation of plant growth-promoting rhizobacteria (PGPR)
Suppression of weeds
