Botanists and soil scientists have been discovering more and more about relationships between plants that have a direct symbiotic relationship with the growths of beneficial fungi in the soil. As a result we need to completely rethink our individual potting routines by introducing these beneficial fungi when we pot and repot our bonsai and pre bonsai trees. In larches, pines and cedars, Mycorrhiza fungi is quite common. It is also found, though in small numbers in the soil of almost all tree species.
One noted study grew 50 identical Scots Pines. (A fantastic bonsai tree!) All of the trees chosen for the study showed basically the same growth at the age of one year. In the study there was no addition of mycelium fungi during planting. In a very short time several of the Scots Pines began to look rather sick, but many were developing great growth and were obviously healthier with nice deep green needles and rapid growth. Later, when inspection of the trees rootballs were examined it was found that the healthy well growing trees had a natural spontaneous mycelium growth. The sick trees had NONE.
You can easily see and notice the Mycorrhiza as it appears as a thin white semi fiberous mass around the roots. With pine species it is very noticeable.
Mycorrhiza active role in the root system is simple. The Mycorrhiza form a basic symbiotic relationship with the plant by helping to transfer nutrients in the root system in a simple exchange for sugars from the plant. Nature at work!
Mycorrhiza in direct association with the plants roots, somewhat surprisingly, seem to behave in the same manner as root hairs do. These Fungi grow then help in the intake of food and water from the soil and they also help the plant increase the acceptable PH range in the soil for the plant. Typically from a pH of 4.5 to 6.6 or perhaps a bit more which varies from species to species. In direct return the plant supplies valuable carbon to the Mychorrhiza which allows the fungi to prosper. A simple, and beautiful symbiotic relationship that allows plants not to just grow. BUT THRIVE.
Soil condition will greatly influence the levels of Mychorrhiza that will be present. Common sense and tests have shown that soil that is not well aerated or has a PH below 5.5 will not simply support the fungi. Use of chemical fertilizers with even moderate rates of phosphorus and even nitrogen will stunt, kill or otherwise not allow the Mychorrhiza to grow and thrive. High nitrogen levels will "burn" the fungi and a plant with high phosphorus seem to do the same according to various studies.
The crux of the Mychorrhiza issue is you must have healthy soil to maintain the fungi. If you don't have healthy soil you will not have healthy trees. Use a good mix of bonsai soil. Sadly many people out there selling bonsai soil use ingredients in the mix that tend to turn to mush after a short while. Use organic fertilizers when at all possible and make sure you add "TRACE ELEMENTS" as well. Don't be afraid to purchase some packaged Mychorrhiza Fungi for Bonsai Soil (sometimes sold by the name Micro Plus) that contains both ECTO & ENDOMYCORRHIZA FUNGI and use it when you repot. Doing so will give your trees a great boost.