During a drought, the trees in a woodland or forest become 'stressed' and may die.  The  reason for their death is not immediately obvious (beyond lack of water), and  it is not possible to ‘transplant’ a mature tree and its complete root system to a lab for detailed investigations.  However, recently, researchers at the University of Innsbruck have taken ‘the lab’ to a set of mature pine and pine trees. The trees were fitted with rugged and waterproof ultra-sound detectors.  Some of the trees had their canopies covered by a ‘roof’ so that the summer rain was denied to the trees, and they essentially experienced a ‘drought’.   Drought stressed trees produce ultrasound ‘clicks’ (faint acoustic waves that bounce off of air bubbles) that can be picked up by the detectors.  Air bubbles or emboli form in the vascular system of the trees when they are struggling for water.  Water is drawn up the xylem vessels by the evaporation of water (via the stomata) from the leaves, there is a continuous column of water.  When the column of water breaks, bubbles form with the xylem vessels and the transport of water to the leaves is reduced.  If the flow of water is substantially reduced the tree will die. The sound detectors found that the spruces produced more clicks than the beeches when water stressed, suggesting more emboli were formed within their xylem tissues.  It may be that the beeches were able to access the deeper reserves of water in the soil, whereas the spruces had a shallower root system. Trees can, of course, reduce water loss from their leaves by closing down their stomates.  But when their stomates are closed, they cannot take in carbon dioxide for photosynthesis and make the sugars / starch that they need for their metabolism.  At the end of the experiment, the trees that experienced ‘drought’ were drenched with water and most recovered well, and their rates of photosynthesis caught up with the ‘control’ groups of trees (those with summer rain).  However, the spruces’ water reserves were somewhat depleted; this was determined by measuring the resistance the tissues offered to an electrical current. The ability to withstand / recover from drought could over time affect the make up of woodlands and forests,  particularly if the trend for hotter and drier summers continues. Interestingly, some work in the United States (at University of Wisconsin–Madison) suggests that young tree saplings that have experienced drought or heat are more likely to survive when transplanted into more challenging areas.  It seems that the soil microbes that young saplings experience can help young trees establish themselves.  Saplings grown in soil (and microbes) that have experienced drought / cold / heat are more likely to survive when later transplanted and faced with similar conditions.  Trees with ‘cold-adapted’ microbes survived better when experiencing Wisconsin’s winter temperatures. The work was conducted with different species of tree in a variety of locations in Wisconsin and Illinois. The transplant locations varied in temperature and rainfall.  It may be that fungi that inhabit the roots of the saplings are involved in these ‘responses’, though the microbial population of the soil is diverse. For more details of this work, follow the link here.

Lichens are plant-like organisms that are rather unusual in that they are an amalgam of two (or occasionally three) organisms : a fungus and algae (or cyanobacterium). They are symbiotic systems, where the partners of the association work together for mutual benefit.  The fungus makes up the bulk of the lichen's form (known as the thallus), it is a complex network of fungal hyphae that surround the algal cells.  The algae (green algae or cyanobacteria) are essential to the association as they can photosynthesise, fixing carbon dioxide and providing both partners with organic carbon compounds (often in the form of sugar alcohols). Some lichen species are brightly coloured. The colour may vary from a golden yellow to a deep red. The pigments responsible for these colours belong to the anthraquinones.  However, these insoluble, phenolic pigments can have toxic effects. To avoid harm by these pigments, the lichen exports* the pigment from the fungal component of the symbiosis. The pigment then accumulates / crystallises on the surface of the lichen. The layer of pigment crystals reflects harmful radiation (in the form of UV light) and also blue light, whilst still allowing enough light to pass through for photosynthesis by the algae / cyanobacteria. Exposure to UV light can damage DNA, inducing mutations.  The pigmentl layer is effectively a ‘sunscreen’ for the lichen. * Recent work at Imperial College and RBG, Kew has identified the genes responsible for pigment production, and the transport of the pigment out of the fungal tissue. In the past, certain lichen pigments were often used to dye clothing materials.    Parmelia saxatilis, also known as grey crottle, was used to dye wool for Harris Tweed.  This lichen is often found growing on tree trunks and gives a red / brown colour to the material. [caption id="attachment_39793" align="aligncenter" width="700"] Lichen and moss growing together  (thanks to Art for photos)[/caption] Woodlands TV has produced two short videos on the biology of lichens :- https://youtu.be/XQ_ZY57MY64     https://youtu.be/0djrOgKtGlk

Most months, Jasper has introduced us to a new fungus or group of fungi that have made their appearance in woodlands,  some on trees or branches or leaves, others simply emerging from the soil.  Some fungi are parasitic or biotrophic requiring a living host organism on which they feed.  Then there are those that live in and feed on dead and decaying matter in the soil; these are termed saprobic or saprophytic.  The structures that we normally see (particularly at this time of the year) are the fruiting or reproductive bodies of the fungus / fungi.  The majority of a fungus exists as a network of microscopic ‘tubes’ that permeate either the host organism, or the soil / decaying matter in which the fungus has made its ‘home’.  An individual tube is known as a hypha and collectively they form a complex network - the mycelium. The fungal mycelia present in the soil form a vast underground network.   Some of these fungi enter into beneficial associations with plants - mycorrhizal associations.  The fungal hyphae wrap themselves around (and sometimes into) the roots of plants and trees, with whom they share minerals and nutrients. Generally speaking, the fungus helps to supply the plant with mineral nutrients (like nitrates / phosphates) and in return receives carbohydrate material from the plant’s photosynthetic capacity.  These mycorrhizal systems form part of what has been termed the ‘wood wide web’.  Dr. Suzanne Simard, a forest ecologist from the University of British Columbia, coined the term to describe the complex relationships between fungi and plants in woodland and forest ecosystems. It has been suggested that (millions of years ago) fungi helped plants transition from their aquatic home to life on land, with the fungal network serving as a ‘root system’.  Fungi (and bacteria) release enzymes (biological catalysts) and these help break down the complex compounds (like lignin, cellulose and starch) present in dead plants and animals.  As a result of this decomposition, humus is formed. Humus is a colloid.  A complex mixture of materials, some in solution, some in suspension. Humus binds the inorganic mineral particles of the soil together, is a store of nutrients and helps water retention.  The fungal network in the soil sequesters enormous amounts of carbon.  The soil is one of the Earth’s main carbon ‘sinks’.   If soil is over-worked or damaged by the intensive and extensive use of chemicals in farming, then it degrades and with it the rich microbial network. Damage to the soil and its complex microbial population can impact on the growth of plants - from the simplest green plants to the largest trees. Not only are soil fungi and bacteria involved in the cycling of carbon and nitrogen, but they help maintain the fertility and structure of the soil.  Soil is the ultimate recycling system, we need to cherish the soil and its fungal and bacterial populations - it helps maintain the ecosystem services on which we all depend.  Without healthy soils, we face a very bleak future.  

It is worth mentioning that while the majority of the hard pyrenomycetous fungi that are the subject of this two-part post are decomposers of dead wood, and therefore invaluable to any woodland ecosystem, there are types that are less benign. For example, one might question why anyone would need to be able to identify the 90 species of Rosellinia, none of which have a common English name and are nearly identical in all aspects aside from their dimensions, until one realises that a number are serious pathogens. Rosellinia desmazieri, for example, can attack living willow trees. There’s a tropical species called Rosellinia bunodes that causes black root rot on a wide range of cash crops like coffee and bananas, while closer to home we have Rosellinia necatrix, another root rotter. Read more...

Spring might be a wonderful season for nature lovers in general, but for those with a specialist interest in fungi, it can be something of a dry period. This past April has been drier than usual and, dare we mention it, the past couple of months of lockdown have kept many of us housebound anyway, with far fewer opportunities to get out and amongst it looking for things of interest. So is there really not that much to see or discover around this time of year? Well, one might think so, but my own eyes were opened recently when Helen Baker on the British Mycological Society Facebook group organised a wonderfully touching initiative to mark the sad and untimely recent passing of the group’s moderator and founder, Richard Shotbolt, whose encouragement and advice has acted as a spur to many a fledgling mycologist over the years. Read more...

Mushrooms may be thin on the forest floor at the moment, but if you raise your eyes you can find more permanent fixtures higher up on tree trunks and stumps in the form of a surprisingly diverse array of tough and hard-wearing bracket fungi. It is a class I have tended to avoid, largely because many of them look so similar, but also because they can be quite difficult to manipulate into aesthetically pleasing photographic compositions. However, this is only if you look at them from a certain angle. Anyone who has ever expressed an interest in the mycological world may well be familiar with the frustrating habit some friends have of sending them “What is it?” messages alongside blurry smartphone snaps of the top of the nondescript muddy brown shelves of certain finds. The crucial thing one has to remember about bracket fungi is always to look underneath.  Read more...

There are many reasons why resupinate or crust fungi fail to attract much in the way of love or attention even among fungi fanatics. For starters, there are hundreds of different types, and the vast bulk of them are incredibly difficult to identify, lacking that one significant feature amongst other identifying criteria such as colour and habitat: a three-dimensional form. They instead appear as flat blotches, skins or coatings of various hues and textures, and mainly on dead standing or fallen trunks and branches, sometimes parasitizing living wood. Read more...

Brackets, crusts and jellies are the most commonly found fungi in the winter months, as I mentioned in my last post on the various species referred to as Witches’ Butter. These categories are essentially descriptive ones, however, aimed at helping one negotiate ones way to the correct pages in general field guides, rather than relating to particular family groupings and relationships based on more scientific principles. One might find countless instances where the dividing line between a particular specimen is not particularly clear. Crusts, or resupinate fungi, often grow as brackets, for example, if the fallen trunk or log they are growing from them is oriented in a particular direction, and a good number possess fruitbodies with a gelatinous texture. Read more...