Plants and fungi have a long history together, with the interaction between these two groups of organisms driving the evolutionary path of each in unique and consequential ways.
Plants, animals and fungi are all grouped into one large branch of the tree of life, but fungi are neither plant nor animal, holding their own unique and individual branch, referred to as a kingdom in the Linnaean taxonomic ranks biologists use to define life on earth.
Plant life on Earth began in oceans, where early plants absorbed nutrients directly from the water. To make the transition to land, plants had to develop a system of attaining nutrients by other means than simply floating in a stream of them.
Evolutionary biologists have studied fossils to discover fungal hyphae (structures similar to roots) inside cells of some of these early plants, suggesting that a symbiotic, or mutually beneficial, relationship developed that enabled plants to internalize the nutrient stream and achieve a major advancement toward life on land.
This symbiotic relationship benefits both plant and fungus since each organism offers the other a new life process it was previously lacking. For plants, fungi helped with nutrient absorption, allowing the, to develop an internal vascular system for transport of nutrients and creating the opportunity for them to grow and evolve outside water, along the shore and ultimately across the landscape.
In return, plants offered fungi a source of food through the carbohydrates produced from sunlight during photosynthesis. Unlike plants, fungi are unable to photosynthesize, or produce their own food. This convergence of biology allowed for advancement of both branches of the life since these two unrelated paths of evolution could then share genetic information across kingdoms.
As plant life expanded into the terrestrial landscape, fungi followed. Today, nearly 90 percent of all plants associate with a soil fungus, which aids in nutrient and water absorption. In many cases, upwards of 80 percent of plants could not survive without their specific fungal partners, making this symbiotic relationship essential to much of the plant kingdom.
While all this sounds like mutual harmony between these two kingdoms, the plant-fungus relationship has some dicey spots as well. Most gardeners think of fungi in a negative light, and many times rightly so, since they are responsible for the majority of known plant diseases. Fungal pathogens often infect their hosts for access to the same stream of carbohydrates that plants willingly share in symbiosis with other “good” fungi.
Back to the good side of this relationship, fungi are a major driver in the decomposition of organic matter throughout the terrestrial landscape. Along with bacteria and other microorganisms, they are the great recyclers that take fallen organic matter from dead plants, leaves and other plant parts and turn them back into the nutrients in the soil, which is of great benefit to plants.
This process is an integral part of all terrestrial ecosystems and a major driver of plant production across the planet today.
These interrelationships are some of the most intriguing aspects of the natural world and have fueled my lifelong fascination with biology. For me, it’s always consoling to consider the co-evolutionary relationship between plant and fungus when dealing with certain plant problems, like a disease-plagued tomato patch this time of year.
Without these intricate relationships, the plant kingdom could not have achieved the diversity we all know and love today.
Ryan Pankau is a horticulture educator with the UI Extension, serving Champaign, Ford, Iroquois and Vermilion counties. This column also appears on his ‘Garden Scoop’ blog at go.illinois.edu/GardenScoopBlog.