Introduction - Recent research - Which trees form which mycorrhizal relationships

Ectomycorrhizal Fungi are, economically, one of the most important groups of fungi. These are the fungi that form a symbiotic relationship with a plant forming a sheath around the root tip of the plant. The fungus then forms a Hartig Net which means that there is an inward growth of hyphae (fungal cell growth form) which penetrates the plant root structure. There are actually seven types of mycorrhiza and 90% of plants form mycorrhiza with fungi, but ectomycorrhizal refers to this sheath forming type.

The fungus then gains carbon  and other essential organic substances from the tree and in return helps the trees take up water, mineral salts and metabolites. It can also fight off parasites, predators such as nematodes and soil pathogens. Indeed, most forest trees are highly dependant on their fungal partners and in areas of poor soil, could possibly not even exist without them. Thus in forest management, if we do not manage for the mycorrhizal fungi, we could be damaging the trees.

Ectomycorrhizal relationships are common in our forests. Most trees will only form one type of mycorrhizal relationship with fungal partners. For instance, Oak, Beech and Birch all form ectomycorrhizal relationships with a number of fungi. This means that these trees are particularly good for finding fungi under. However, Ash and Sycamore for instance form Vasicular-Arbuscular mycorrhizal relationships. This type of mycorrhiza does not form fruiting bodies - if ectomycorrhizal fungi appear to be fruiting under these trees, they will be attached to the root tips of another tree a bit further away!!

Boletus ferrugineus

Mycorrhizal Fungi are a popular topic of research. Modern DNA techniques are beginning to give us an insight of what is actually going on under the ground and the first thing this research is saying is that what appears to be happening from looking at fruiting bodies above ground is not typical of the dynamics under ground!! Here are some of the research findings recently uncovered by Lena Jonsson of the the Swedish University of Agricultural Sciences in Uppsala in her PhD (Community Structure of Ectomycorrhizal Fungi in Swedish Boreal Forests, Doctoral Thesis, Swedish University of Agricultural Sciences, Uppsala, 1998).

  • Between 60,000 and 1.2 million ectomycorrhizas were found in one square metre of forest and 95% of the root tips examined had formed an ectomycorrhizal partnership.

  • In an examination of a 100 year old Norway Spruce forest, the above ground fruiting densities did not bear much resemblance with the mycorrhizal biomass. The 12 species that accounted for 74% of the fruiting bodies only accounted for 30% of the mycorrhizae. Species that did not produce conspicuous fruiting bodies accounted for at least 50% of the mycorrhizas and ascomycetes accounted for 20% of the mycorrhizal abundance. 

  • Individual mycorrhizae are not perennial structures and it has been shown that 60% of the individual mycorrhizae last for longer than 6 months and 25% last more than 16 months. 

  • When seedlings regenerate in a forest, they form their ectomycorrhizas with whatever fungi there are in that area. The ectomycorrhizas that form do not depend on the age of the tree. As ectomycorrhizas mainly form in the upper layers of soil, if the soil is disturbed by digging trenches, this drastically reduces the ectomycorrhizas available to the seedling and hence its chances of survival. This is an important thought in terms of forest management.

  • There has long been the concept of mycorrhizal succession as different species differ in their ability to establish themselves from spores and in mycorrhizal colonisation. However, for the reasons stated in the last point, this succession may not always occur as "late-stage" species will colonise saplings where the saplings are growing in a healthy mixed aged forest.

Russula mairai

 

  • In old forests, the ectomycorrhizal community is often made up of large fungal individuals. In the genus Suillus, individuals can often extend over 100m2. The Scandanavian sites suggest that most forests are dominated by a few species that dominate under ground with most other species having low densities.

  • It has long been known that increased nitrogen due to atmospheric pollution has meant that the ectomycorrhizal fruiting bodies decrease in numbers. This has been a pressing concern for conservation for some time, but it now appears that increased nitrogen does not actually harm the mycelia under the ground, just the ability to produce fruiting bodies. This might be a long term problem for the mycorrhiza rather than a short term problem however.

  • It is thought that a high ectomycorrhizal diversity is important in the healthy functioning of a woodland. Different fungi appear to have different roles. Some may be better at helping the tree take up particular nutrients, others may be specialised at protecting against pathogens, others in enzyme production.

  • It has long been thought that many years of intensive survey are needed to produce an ectomycorrhizal species list if identifying species from fruiting bodies. Studies in Scotland showed that after 20 years, the number of new species found was still not tailing off in a Caledonian Pine forest site. An interesting thought raised by Jonsson is that this assumes that the below ground mycorrhizal community is stable. But mycorrhizae are more or less annual and that their formation depends on the availability of carbohydrates from the trees. This carbohydrate production is variable depending on the levels of photosynthesis and tree growth, thus the ectomycorrhizal community under ground will probably also change meaning that there could always be room for new species. So, the situation is dynamic and there could never be a "complete" species list!

Amanita excelsa

 

Which trees, shrubs and flowers form ectomycorrhizal partnerships? The information here comes from "A Checklist of Mycorrhiza in the British Flora" by J.H.Harley & E.L.Harley. New Phytologist (1987) (Suppl.) 105, 1-102. This paper lists references that refer to the mycorrhizal relationship that a particular plant forms. Different types may be quoted in different papers and generally no attempt is made to review each reference. For instance, the Male Fern, Dryopteris felix-mas, is listed 14 times as forming vasicular-arbuscular mycorrhiza and 3 times as ectomycorrhizal. So beware of this and be careful about associating an ectomycorrhizal fungus with Ash, Elm, Yew or Sycamore!  Ecto stands for ectomycorrhizal, VA for vasicular-arbuscular. 

Trees and Shrubs

 

Firs - all species

Abies spp.

Ecto

Field Maple

Acer campestre

4 VA, 2 Ecto

Norway Maple

Acer platanoides

5 VA, 1 Ecto

Sycamore

Acer pseudoplatanus

21 VA, 4 Ecto

Horse Chestnut

Aesculus hippocastaneum

VA

Alder

Alnus glutinosa

7 Ecto, 3 VA, 1 ectendo

Grey Alder

Alnus incana

4 Ecto, 1 VA

Dwarf Birch

Betula nana

Ecto

Silver Birch

Betula pendula

Ecto

Downy Birch

Betula pubescens

Ecto

Box

Buxus sempervirens

VA

Hornbeam

Carpinus betulus

Ecto

Sweet Chestnut

Castanea sativa

Ecto

Hazel

Corylus avellana

Ecto

Midland Hawthorn

Crataegus laevigata

2 VA, 2 Ecto

Hawthorn

Crataegus monogyna

3 Ecto, 1 VA

Spindle

Euonymus europaeus

VA

Beech

Fagus sylvatica

Ecto

Alder Buckthorn

Frangula alnus

7 VA, 1 Ecto

Ash

Fraxinus excelsior

14 VA, 2 Ecto

Holly

Ilex aquifolium

4 VA, 1 Ecto

Walnut

Juglans regia

1 VA, 1 Ecto

Juniper

Juniperus communis

2 Ecto, 5 VA

Larch - all species

Larix spp.

Ecto

Privet

Ligustrum vulgare

VA

Common Mallow

Malus sylvestris

5 VA, 2 Ecto

Silver Spruce

Picea abies

Ecto

Sitka Spruce

Picea sitchensis 

Ecto

Black Pine

Pinus nigra

Ecto

Maritime Pine

Pinus pinaster

Ecto

Scots Pine

Pinus sylvestris

Ecto

Poplar - all species

Populus spp.

Ecto and VA

Wild Cherry

Prunus avium

6 VA, 3 Ecto

Dwarf Cherry

Prunus cerasus

Ecto

Bird Cherry

Prunus padus

2 VA, 2 Ecto

Buckthorn

Prunus spinosa

VA

Douglas Fir

Pseudotsuga menziesii

Ecto

Wild Pear

Pyrus pyraster

4 Ecto, 3 VA

Oak - all species

Querus spp

Ecto

Purging Buckthorn

Rhamnus catharticus

VA

False Acacia

Robinia pseudacacia

5 VA, 1 Ecto

Willow - all species

Salix spp.

Ecto and VA (at different stages?)

Elder

Sambucus nigra

VA

Red-berried Elder

Sambucus racemosa

7 VA, 2 Ecto

Whitebeam

Sorbus aria

3 VA, 3 Ecto

Rowan

Sorbus aucuparia

12 VA, 4 Ecto

Wild Service Tree

Sorbus torminalis

Ecto

Yew

Taxus baccata

VA

Small-leaved Lime

Tilia cordata

10 Ecto, 2 VA

Large-leaved Lime

Tilia platyphyllos

Ecto

Common Lime

Tilia x vulgaris

Ecto

Gorse

Ulex europeus

VA

Wych Elm

Ulmus glabra

VA

English Elm

Ulmus procera

5 VA, 1 Ecto

 

Flowers and Ferns

 

Bearberry

Arctostaphylos uva-ursi

Ecto, Endo, Ericoid, Arbutoid, Ectendo

Male Fern Dryopteris felix-mas 14 VA, 3 Ecto

White Rock Rose

Helianthemum apenninum

VA, Ecto, Ectendo

Hoary Rock Rose

Helianthemum canum

VA, Ecto, Ectendo

Common Rock Rose

Helianthemum nummularium

VA, Ecto, Ectendo

Purple Colt's Foot

Homogyna alpina

6 VA, 1 Ecto

Wall Lettuce

Mycelis muralis

5 VA, 1 Ecto

Alpine Bistort

Polygonum viviparum

9 Ecto, 1 VA

Wild Madder

Rubia peregrina

Ecto

Moss Campion

Silene acaulis

3 VA, 1 Ecto

Wood Vetch

Vicia sylvatica

2 Ecto, 1 VA

 

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