Root Grafting Enhances Growth

trees on dry land against a blue sky and white clouds

Biological Strategy

Jack pine

Mary Hoff

Image: Chris M Morris / Flickr / CC BY - Creative Commons Attribution alone

Cooperate Within the Same Species

A species is a group of organisms capable of breeding to produce fertile offspring. When individuals within a species undertake activities that benefit one another, that cooperation benefits not just the individuals, but also local and wider populations of that species. Collaborating in activities such as finding food, controlling parasites, and protecting from predators enhances overall survival. To cooperate, there must be enough benefit to an individual, and especially to a population, to justify any risk taken by individuals. Through cooperation, risk is distributed among individuals and the benefits to the community are greater than the sum of the benefits to individuals. An example is birds that gather in flocks, a cooperative activity more beneficial than acting alone. While some birds forage, others watch for predators. When one finds food, others also feed on it. Despite potential short-term competition for an individual that finds food, over the long-term, that same individual benefits when others find different food sources.

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Distribute Liquids

Liquids include water, as well as body fluids such as blood, gastric juices, nutrient-laden liquids, and more. To survive, many living systems must move such liquids within themselves or between locations. Because of their properties, liquids tend to disperse unless they are confined in some way. To address this, living systems have strategies to confine fluids for transport, and to overcome barriers such as gravity, friction, and other forces. Some of these same barriers also provide opportunities. Trees and giraffes face the same challenge: how to move fluids (water and blood, respectively) upward against gravity. But their strategies are quite different. The tree moves water using capillary action and evaporation, possibly due to water’s properties of polarity and adhesion. The giraffe’s tight skin provides pressure to assist in blood circulation. and keep blood from pooling in the legs.

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Capture, Absorb, or Filter Liquids

The most common liquid used by living systems is water, which they require to survive. But there are many other liquids that provide nourishment, play a role in defense mechanisms, or serve other purposes. Water varies in its availability; it is sometimes plentiful and sometimes very scarce or only available as fog or mist. To minimize the energy required to capture, absorb, or filter liquids, living systems have strategies that take advantage of the unique properties of the given liquid. For example, water moves from a gaseous to liquid state when it encounters a surface colder than the air. Plants in forests that experience fog and clouds more than rain have strategies that condense liquid water from moist air.

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Conifers and Others (Pines, Spruce, Gingko)

Clade Gymnosperms (“naked seeds“): Conifers, cycads, Gingko, gnetophytes

There are approximately 1,000 known species of Gymnosperms. These include well known needle-bearing plants like pines, firs, and spruce, as well as some with broad leaves like the Gingko and the gnetophytes. Instead of flowers, gymnosperms produce unenclosed (“naked”)seeds exposed on the surface of cone scales. Economically, conifers make up 45 percent of the world’s lumber production. The first gymnosperms evolved over 390 million years ago in the Paleozoic Era and dominated landscapes for a quarter of a billion years before the evolution and diversification of flowering plants.

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Roots of jack pines distribute limited resources by forming underground connections between trees.

Introduction

Above the surface, jack pines (Pinus banksiana) in a stand seem to be independent individuals. A look beneath the soil, however, reveals a different story.

A hardy tree found in the northern U.S. and Canada, jack pine thrives on sandy and thin soil and is often among the first tree species to come back after a fire. It commonly grows in stands, sometimes interspersed with other tree species such as black spruce. But it’s the connections they make with others of their own species that give them an advantage when facing such harsh environments.

Once a graft forms, trees can share resources through the connected roots, often among multiple individuals connected by the unseen web beneath the soil.

The Strategy

When one jack pine tree’s roots run into the roots of another, they may press into each other. The roots begin to add cells along the pressure points until the bark between them breaks through.

As the tissues from the two plants contact each other directly, the individual cells start to stick together. The surrounding tissue deposits sugar molecules, creating an even stronger bond. New cells develop and eventually form xylem and phloem, the woody vessels that carry food, nutrients and water.

The result is a shared root structure that often contains root material from both trees. Once a graft forms, trees can share resources through the connected roots, often among multiple individuals connected by the unseen web beneath the soil.

Although grafts initially reduce individual tree growth, in the long run they appear to benefit the stand as a whole. The shared roots allow trees growing in more favorable conditions within the stand to give weaker, disadvantaged trees a boost. They allow stumps to stay alive, helping to crowd out potentially competing tree species. And because up to 70% of the stand may form grafts, they provide added stability against strong winds.

Image: mricon on Flickr / CC BY SA - Creative Commons Attribution + ShareAlike

Jack pines that grow near each other can form connections between their roots that help the individual plants thrive.

Individual jack pine trees can connect underground when their roots contact each other and break through the bark separating them.

Tissues from individual trees physically connect, permitting the movement of food, water, and nutrients between them.

Image: Pancrace Bessa / Public Domain - No restrictions

Pancrace Bessa drew this illustration of Pinus banksiana in the early 1800s.

The Potential

Making deep connections between individuals facing different challenges can allow for the effective flow of resources and information in human and technological settings as well as in underground root systems. This strategy of creating a “sharing economy” offers valuable insights into how, even if they initially come at a cost, collaborations can create a stronger, more resilient overall system to the ultimate benefit of both contributors and recipients.