Benefits to crop production from mycorrhiza

Question 1

Mycorrhizal fungi absorb nutrients from soil and pass these on to plants

Answer 1

The plants supply the fungi with sugar and lipid from photosynthesis - a mutual symbiosis

Question 2

Hyphal lengths - typically 10-100x longer than roots

Leake et al, 2004

Answer 2

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

Question 3

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…

Answer 3

However- most boreal forest trees have ectomycorrhiza, as do many temperate forest species (angiosperms: beech, oak, birch, hazel…
gymnosperms: pine, spruce, larch, fir…)

Question 4

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.

Answer 4

NOT found in
Brassicas: oilseed rape, cabbages, mustards, etc.
Amaranths: sugar beet, quinoa, etc.

Question 5

How do we measure arbuscular mycorrhizal fungi?

Spores, microscopy, lipid markers and DNA

Answer 5

Use of the signature fatty acid 16:1w5 as a tool to determine the distribution of arbuscular mycorrhizal fungi in soil

Question 6

Standard primers used for DNA identification of AM fungi do not detect Mucoromycotina.

Answer 6

Their importance has been hidden until recently.

First evidence of mutualism between ancient plant lineages (liverworts) and Mucoromycotina fungi (Field et al, 2018)

Question 7

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

Answer 7

The circumference of the Earth at the equator is 40,075km

Question 8

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

Answer 8

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!

Question 9

(Johansson et al., 2004)

SEE SLIDES (Lecture 10)

Answer 9

Significance of microbial interactions in the mycorrhizophere for sustainable agriculture

Question 10

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:

Answer 10

Fine roots diameter 100 - 500 µm
Root hairs >10 µm
AM arterial hyphae 20-30 µm
AM feeder hyphae 2-7 µm

Question 11

Translocation down hyphae to roots is faster than the rate of diffusion of P in solution.

Bieleski (1973) estimates 1000 x faster.

Answer 11

Higher affinity P uptake in mycorrhizal compared to non-mycorrhizal plants of the same species.
(Cress et al., 1979)

Question 12

Marschner 1995

Answer 12

The role of mycorrhiza in plant P uptake and plant growth depends on plant and fungal characteristics

Question 13

AM mycelia extend the width of the P depletion zone around roots

Answer 13

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)

Question 14

Potential fertilizer saving by AM- Cassava often grows in P deficient tropical soils

Answer 14

(Marschner 1995)

Question 15

Mycorrhiza often synergistically operate with plant-growth promoting rhizobacteria

Answer 15

some bacteria involved in P solubilisation may help reduce the need to add P fertilisers. (Harris et al. 2006)

Question 16

One-time tillage of no-till: effects on nutrients, mycorrhizae and phosphorus uptake

Answer 16

Garcia et al 2007

tillage reduced AM colonisation

Question 17

Conventional ploughing and disking disrupts AM fungal networks and reduces P uptake

Answer 17

Kabir et al 1998

Question 18

Soil aggregation and carbon sequestration are tightly correlated with the abundance of arbuscular mycorrhizal fungi: results from long-term field experimnts

Answer 18

Wilson et al 2009

Water-stable micro-aggregates increase with AM

Question 19

Mycorrhizal fungi increase the energy required to break down soil aggregates

Answer 19

macroaggregates> 2mm

Question 20

3 year grass-clover ley after continuous arable –rebuilds mycorrhiza activity and boots wheat growth

Answer 20

pasture > 3 year ley > Arable

for shoot biomass, root biomass and arbuscule abundance (in general)

Question 21

AM – the costs and benefits are not shared equally between plants and are fungus specific

Answer 21

Van der Heijden et al 1998

Mycorrhizal – but 
unresponsive
Mycorrhizal
responsive
Non-mycorrhizal

Question 22

Plant species differ in their abilities to assist aggregate formation
Macro-aggregate stability is increased by hyphae (and possibly a hydrophobic glycoprotein glomalin)

Answer 22

(Rillig et al., 2002)

Question 23

LOOK AT SLIDES 34

Answer 23

TO 51

leys and AM and legumes

Question 24

Mycorrhiza-induced resistance: more than the sum of its parts?

Answer 24

Cameron et al

Question 25

Mycorrhiza helps sunflower to suppress weed biomass-

Answer 25

both in weed species that form mycorrhiza and those that do not.

Question 26

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

Answer 26

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

Question 27

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)

Answer 27

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