Durham University Botanic Gardens in October

By my next visit to the Botanics, towards the end of October, everything changed and leaves of every hue of gold and red are everywhere as deciduous trees do their best to recoup the carbon and nitrogen stored in their leaves before these are shed.  The oaks and maples in the North American arboretum are particularly spectacular, perhaps unsurprisingly.

Autumn leaf collage

The other new attractions in October are fungi – a warm, wet autumn after a dry spring is perfect for encouraging them to produce fruiting bodies and they are everywhere.  The grassland below Hollingside House and the deciduous woodland beyond the Fungate are hotspots and the stump of the Monkey Puzzle tree is covered with the fruiting bodies of the Honey fungus, Armillaria mellea, which led to its demise.

Armillaria mellea growing on the stump of the old Monkey Puzzle tree, Araucaria araucana
Armillaria mellea growing on the stump of the old Monkey Puzzle tree, Araucaria araucana

Unlike the many species of mycorrhizal fungi which are so important in helping trees grow, Honey fungus is a pathogen causing white root rot in trees and shrubs it infects.  The fungus breaks down cell wall materials such as lignin and hemicellulose in the plant roots to supply itself with food. Because it can grow as a saprotroph on dead wood, surviving for up to 50 years on dead tree stumps as well as on living roots, there is no need for the fungus to keep its host tree alive. Honey fungus produces thick mycelial cords or rhizomorphs under the tree’s bark. These rhizomorphs, which look very like new roots, can spread outwards from an infected tree or shrub to its neighbours at a rate of about a metre a year – one of the reasons gardeners fear it so much. The fungus can attack not just trees but also roses, rhododendrons and other garden favourites.

Many of the other fungi I was able to identify are also saprotrophs, feeding on leaf litter and dead wood, giving some indication of this habitat’s value.  I found huge Clouded funnel fungus (Clitocybe nebularis) growing amongst conifers in the arboretum and tiny translucent Porcelain fungus (Oudemansiella mucida) growing on fallen beech trees in the deciduous woodland past the Fungate. Delicate as it seems, Porcelain fungus fights to secures its niche and outcompete other fungi by secreting strobilurin, an antifungal agent which inhibits mitochondrial function in competitors, preventing their growth.

Turkeytail fungus, Trametes versicolor, is one of the prettiest of the rot fungi and is less fussy about which deciduous wood it grows on than some species. The same is true of the Wrinkled crust fungus, Phlebia radiata. However I also found the less common Beech Jellydisc fungus, Neobulgaria pura, growing on fallen beech logs. The website First Nature says the fungus may get its generic name from the word bulgar, for a leather wine pouch, though I have to admit I couldn’t substantiate this!

4 Fungi. Clockwise from top left: Clouded funnel, Porcelain, Beech Jellydisc and Turkeytail fungi
Clockwise from top left: Clouded funnel, Porcelain, Beech Jellydisc and Turkeytail fungi

The fruiting bodies of all these rot fungi, in turn, go on to provide a rich source of food for a range of insects and small mammals, including moths and gnats whose caterpillars and maggots, respectively, feed specifically on fungi.

The Ceratomyxia fruticulosa (Coral slime mould) I found on fallen beech branches is another wood-rotting organism.  It belongs to a fascinating group, the plasmodial slime moulds, which used to be classified as fungi but which are now recognised as amoeboid protists, part of the same supergroup (Amoebozoa) as organisms such as Amoeba itself. Slime moulds are real oddities – unusual in the Amoebozoa in having a macroscopic part to their four-stage life cycle, where individual cells stick together to form a thin, multinucleate plasmodium. All the nutrients absorbed by the colony are then distributed evenly thoughout the whole ‘body’, which moves slowly over the surface of its chosen substrate by flowing in an ameboid fashion, in search of food.

Eventually, sporangia bud off from this plasmodium, before developing the stalked spores seen below.

Spore producing stage of the slime mould Ceratiomyxa fruticulosa (synonym C. porioides).
Spore producing stage of the slime mould Ceratiomyxa fruticulosa (synonym C. porioides).

These spores, once released, develop into individual microscopic swarming cells, each with four haploid nuclei and a flagellum.  At some point, dictated by local environmental conditions, a number of these cells fuse to form a new plasmodium and so it continues… See April’s Monthly Mushroom : Coral Slime (Ceratiomyxa fruticulosa) (woodlands.co.uk) for more on these fascinating organisms. However, there are also mycorrhizal fungi to be found in the woods and grassland.  Text Box: Xerocomos chrysenteronThe bolete, Xerocomos chrysenteron (an aggregate rather than a single species) is a mycorrhizal fungus associated with the roots of beech trees in the deciduous woodland but is also, evidently a food source for other types of organism!

Bolete fungus Xerocomos chrysenteron
Xerocomos chrysenteron

It’s not just fungi which are feeding animals at this time of year – it’s been a mast year for berries and nuts and the ground has been covered by fallen acorns and sweet chestnuts. The chestnuts were large enough this year to be worth collecting, which is not common in NE England, and we had one good meal from them.  I had to be quick though, to beat the local squirrels to it!

Sweet chestnuts

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