Since plants, as autotrophs, fix their own carbon from atmospheric CO2 their other nutrient requirements are filled with dissolved nutrients taken up with their roots. Plants major requirements from the soil are N-P-K.
Nitrogen is used in building all proteins whether in a plant or an animal. Nitrogen is also part of chlorophyll. When nitrogen is deficient, plants concentrate it in their youngest leaves, so the older, larger leaves turn pale, and in severe cases may wither and fall. Because nitrogen is so often the limiting factor to growth plants will take up more than they need deregulating their growth. They have no feedback to slow nitrogen uptake.
Phosphorous is required to build ATP so is needed in both plant's & animal's mitochondria. This same ATP is part of the DNA as one of the four bases dATP (deoxy-adenosinetriphosphate) so is also critical to constructing DNA. Phosphorus is essential to the moving and storing of carbohydrates in the form of sugars and starches. Without sufficient phosphorus plants will be stunted though the leaves, instead of being pale as with insufficient nitrogen, will be purplish from the accumulated sugars. Photosynthesis will produce glucose that cannot be utilized in the absence of sufficient phosphorus.
Third of the NPK nutrients is potassium. Potassium plays a role in water transport but more important to photosynthesis. Potassium is critical in ATP production so can influence photosynthetic rates. Potassium influences the processes of plant food creation, transportation, and storage.
Other minor nutrients include calcium, magnesium, and sulfur. Calcium is important because of the critical role it plays in the structure of cell walls, especially at the growing tips of both roots and tops. Magnesium is the central element in chlorophyll. Sulfur is also essential in building proteins. Other micronutrients are boron, copper, iron, manganese, molybdenum, zinc, and iodine.
Plants have symbiotic relations with mycorrhizal fungi. - 85% of all plant families, including grasses, form endomycorrhizal symbioses. Even moss will form associations with glomeromycete fungi and their thallus since they have no roots.
Less common are the ectomycorrhizal partnerships. Ectomycorrhizal fungi are mostly known to form a partnership with trees.
The sponge mushrooms like the morel form mycorrhizae with trees including Larix occidentalis, Pinus contorta, Pinus ponderosa, and Pseudotsuga menziesii (members of the pine family).
http://www.morel-farms.com/discovery.html