Now I don't want to put anyone off by disappearing into jargon so I'll keep this as straight forward as I can..
The point of this particular thread was to examine and discuss the relative usefulness of applying sugar (simple carbohydrate) solutions to the soil and root environment of trees in terms of boosting the health and vigour of those trees.
Why sugar?....trees cannot take up sugar molecules from the soil..so whats the point???
Well to understand the importances of simple sugars in the soil and root environment you need to start looking at the soil in a slightly different way, instead of seeing and concieving of it as "dirt" you need to see it as a living web of interrelated organisms...many very very small (bacteria) and some very familiar and large (worms, beetles etc). All these organisms interact with each other compete for physical space and resources...they make up what is called the soil food web. Lets put to one side for a moment the unnatural state of our urban soils and look at the model...
Now Treelore is correct that it is possible when examining what is going on in the soil food web for a particular vegetative community...
prairie grass lands for example...to identify a dominance of certain elements of the web in relation to others, he points out that grass lands tend to have a greater ratio of bacteria to fungi...ie bacteria dominate the microscopic levels in the web, what is termed the first trophic level. Because the bacteria dominate this first (bottom if you like) level in the web it has a cascading effect throughout the web and the physical and chemical characteristics of the soil generally......the soil environment (soil food web) that evolves under a grass dominated community is (in theory) far from ideal for normal healthy tree growth. (I'll return to this later...please bear with me!!!!)
But what has this to do with sugar!!!!!
The simple carbohydrates that sugar represents, be it sucrose, glucose or fructose are essential to the life cycle of both bacteria and fungi....indeed the payoff for those mycorrhizae is that the tree delivers carbohydrate direct to the fungi, the theory/model if you like is simple; when mycorrhizae are present in a relatively healthy soil the introduction of simple sugars....sugar water.....will produce accelerated fungal growth, increasing the chances of root inoculation.
Simple sugars are also stimulants for bacteria...yes, but
not exclusively, one of the problems I and others have with some minor aspects of the way the soil food web model is applied is precisely this kind of confusion.
Vegetative communities that are dominated by grasses do support very long lived healthy tree growth...not closed canopy forests, no, not old growth forest, but open Eucalyptus and Melaleuaca forests are very significant to the evolution of our continent.
The oldest trees in the UK and some parts of Northern Europe are found in woodland pasture, not in old growth closed canopy forest...and yes I know that is a reflection of the human agricultural influences on the land and the vegetation but nevertheless these veterans are there, and where human impacts are minimal (no road or house building etc) they are living out their life cycle relatively unaffected by the presence of large volumes of grass species as an understorey.
Nobody is suggesting that merely by applying sugar solutions alone structural problems in the ecosystem of the soil can be redressed..that is not the case.
Sugar solutions or sugar water if you like should be part of a comprehensive program of plant health care...that begins with establishing what is going on (or not going on) in the soil and around the roots of the tree in question, thensets about trying to redress some of the problems that we can affect...some we cannot as arborists working on a single site have any immediate impact on eg disappearing ground water!
Carbon loss is often the single most important aspect of the soil ecosystem that requires attention...applying mulch in the form of aged wood chips and forest mulch ideally from the same mix of species that make up the ecosystem being worked on...... The purpose of the mulch the carbon source is to provide fuel for the soil food web, sugar water and compost teas (brewed deliberately to replace identified short falls in the exisiting food web) are the stimulants to kick start the process of decomposition that is critical to all the cycling going on in the soil.
Sugar solutions as part of a wider program of soil works are very good for trees indeed....and it is a mistake to think that fungi are not predisposed to breakdown sugars when they are available in the soil...that is precisely what they do and thank the gods they do too...the so called "sugar fungi" (together with bacteria) immediately absorb the simple sugars and amino acids and the explosion in the population of "sugar" decomposers is critical to the functioning of the next trophic level in the soil food web...ass the simple compounds are used up these "sugar" fungi decline, but their excretory products and they themselves become part of the mineralisation process in teh soil and lead into the decomposition of more complex organic compounds.
I know its getting complicated to follow......
What I'm trying to say is that the many very critical fungi species (critical to the health of trees) are stimulated directly and indirectly by the addition of simple sugars to the soil and root environment...yes bacteria are stimulated too and that is a
good thing.
Models are essential to our understanding very complicated sets of relationships...3D relationships at that! However models sometimes give us a falsely simplified view of those relationships......
The rhizosphere is a tiny and emmense environment all at the same time, it is constantly in flux. the micro biology of the rhizoshere around the roots of an ancient oak in open pasture in a field in Scotland is different to that found 20 metres away in the soil around the hawthorn hedgerow.
Its even more interesting (and complex) in areas like the Mitchell grass lands of Western Queensland...where my love Michelle lives (AKA the explorers tree Hughenden)...but maybe for another thread eh?
(hope I didn't put you all to sleep
)