The Roots of Change: How Human Activity is Altering Plant Interactions with Fungi

Driven by human activities, the earth’s climate is changing faster than in the geologic past, leading the present geological epoch to be dubbed the Anthropocene. Within our own lifetime, we are seeing record-breaking increases in temperature and CO₂ concentration, and the impacts of these changes are being felt species-wide and at an unprecedented scale.

Motivated by an interest in the diversity in plants and how anthropogenic activities are affecting natural evolutionary processes, post-doctoral researcher Dr. André Duarte and Dr. Hafiz Maherali, a professor in the Department of Integrative Biology, recently examined the effects of climate change on the mutualistic relationship between plants and arbuscular mycorrhizal (AM) fungi.   

“One of the most widespread ecological interactions that influences plant fitness is the mutualistic symbiosis between plants and mycorrhizal fungi,” says Maherali.

This symbiotic relationship consists of the exchange of resources and services that enhance the growth and survival of each organism. Plants provide fungi with sugars from photosynthesis, while in return, AM fungi use their large system of nutrient absorbing structures (called hyphae) to provide the plant roots access to phosphorus and nitrogen resources in the soil. AM fungi also offer plants enhanced water uptake, protection from several pathogens, and herbivore defenses.

“It’s an ancient mutualistic relationship that has existed for over 460 million years,” says Maherali.

It is also believed to be what facilitated the transition of ancestral plant species from aquatic to terrestrial environments. This major historic event led to the evolution of a large variety of terrestrial vertebrate and invertebrate organisms, including humans and majority of life on earth as we know today. But today’s rapid environmental change now provokes the question: how will such foundational interactions be affected by climate change?

To answer this question, Duarte and Maherali conducted a meta-analysis of over 50 different studies looking at the effects of experimentally applied increases in CO₂ concentration and/or temperature on the responses of wild and domesticated plants to AM fungi. A meta-analysis is a tool used by researchers to statistically analyze the results of many independent experiments, looking for an overall effect or general trend.

Intriguingly, the results suggest that a rise in temperature may strengthen the mutualism with AM fungi in wild plants, but not in domesticated plants.

Domestication is an evolutionary process where species adapt in response to human agents of selection. In modern agriculture, for example, chemical fertilizers are widely used to maximize crop yields by increasing nutrient availability. If AM fungi attempt to colonize plant roots in an environment where nutrients are abundant, the fungi’s acquisition service is no longer needed, but the plant must still pay the carbon cost of supporting the fungus. Thus, the mutualistic relationship becomes parasitic, leading to selection that reduces the ability of AM fungi to colonize plants.

In contrast, the meta-analysis showed that changes in atmospheric CO₂ concentrations may have negligible impacts on the mutualism in either type of plants.

This study presents a valuable first step to an in-depth understanding of how mutualism responds to climate change, but there is still work to be done. For example, while Duarte and Maherali’s finding suggests that either rising temperatures or CO₂ concentrations alone may not harm mutualistic interactions, we don’t yet understand how they impact mutualism in combination. It is also unclear what role other anthropogenic- and climate-related changes, such as nutrient deposition and release of pollutants, may play.

Leo Tolstoy famously stated: “One of the first conditions of happiness is that the link between man and nature shall not be broken.” Today, that quote takes on a greater sense of urgency than ever. But Maherali instills a sense of hope and optimism for environmental recovery, which can be aided by a profound understanding of the natural processes impacted by the rapid global change. 

“It’s really about protecting and restoring habitat,” says Maherali. “It is about managing both our own needs as a species in terms of both habitat, food and the requirements of other species we share the planet with.”

Read the full article in the journal Ecology and Evolution.

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