Relationships between plants and fungi
Stealing for survival
Some fungi are parasites on plants, and some plants are parasites on fungi. In both situations, one of the partners steals resources from the other to reproduce and survive. Parasitic fungi affect both wild and cultivated plants, sometimes causing extensive damage that can be very costly for the agricultural and horticultural industries. Some of these fungi include rusts, smuts, and moulds, but can also include mushrooms like the forestry pests, Armillaria spp. Plants parasitic on fungi are primarily found only in the wild and their effect on fungal ecology is less well understood.
Mutually beneficial relationships
On the other end of the spectrum, plants and fungi engage in mutually beneficial relationships, the most important of which is called mycorriza (plural = mycorrhizae) where fungi live on and in the plant’s roots. In this case both the plant and the fungus depend on this relationship to develop and survive. This special symbiosis ('living together') is known as a 'mutualism', where both partners benefit from each other. It is estimated that as many as 90% of all plants depend on mycorrhizae to survive, and mycorrhizae probably enabled plants to colonize land around 450 million years ago.
'Outside fungus root'
A special type of mycorrhiza, where the fungus forms a sheath around the root tips of the plant (termed 'ectomycorrhiza' or 'outside fungus root'), forms between 10% of plant species and around 5,000 species of fungi. The fungus receives sugar from the plant in return for greatly enhancing the plant’s ability to take up water and nutrients from the soil. Other benefits to the plants may include protection against herbivores and resistance to toxins and pathogens.
Ectomycorrhizal relationships dominate in temperate forests – and more recently their importance in tropical forests is being established. For example, the ends of the fine tapia tree root (pictured, right) are covered in a dense layer of interwoven white fungal filaments, which envelop the tip of the root like a glove creating a plant-fungus interface (ectomycorrhiza). Through this interface the plant exchanges sugars for minerals, water, and protection from the fungus.