New microbial partnerships provide support for trees under climate stress

Climate change exposes plants to rapid shifts in temperature and precipitation, pushing them into new ranges and squeezing them into old ranges.

It may be easier to adapt trees either way by making new microbial friends underground, according to new research from the University of Wisconsin-Madison published today in the journal Nature. Sciences.

Plants survive through wide ranges of heat, cold, rain, and drought, but they don’t fill their niches on their own. Along with the animals and insects that live on and around a tree — swarming in now and then to help pollinate, control pests, or disperse seeds — there are countless soil microbes (such as various fungi that grow alongside tree roots). These microbes can relieve the stresses of natural life by helping trees attract more nutrients and water or influencing the time they germinate or flower to better match seasonal conditions.

This relationship could play an important role in climate adaptation.

“Climate change is adding new stresses faster than most trees are used to,” says Richard Lankao, a professor of plant pathology at the University of Wisconsin-Madison. “We have some sense of how most tree species will react — where they will be pushed out and where they can move. But that depends on what we think the trees themselves can handle. Forests might actually be more resilient if we give them credit for changing microbial communities.”

To test how communities of microbes from different regions affected stressed trees, Langau, along with research scientist Cassandra Alsop and research specialist Isabel George, transplanted the trees at the far edges of their current ranges. Seedlings of a long list of deciduous species—oak, elm, hickory, maple and more—have descended to the ground some 450 miles away in plots in northern Wisconsin and central Illinois.

Before the trees were moved to remote plots, they were germinated from seed in UW-Madison greenhouses in different soil samples collected from 12 sites in Illinois and Wisconsin, creating distinct microbial relationships. Some of the trees were grown in familiar soil collected near the central part of the tree ranges. Some were introduced to the new microbial communities by germinating in soil collected from locations physically closer (or more in typical temperature and precipitation conditions) to the experimental plots in which they would live for three years.

Up north at the University of Wisconsin-Madison’s Kemp Natural Resources Station, where broadleaf forests naturally give way to forests dominated by evergreen trees, the effects of the relationships between trees and microbes are stark.

“All trees survived the summer just fine, unless they were eaten by a deer,” says Lankao. “It’s a cold winter where we’ve seen successful detachment. Seedlings exposed to microbes from northern locations were more likely to survive the winter than those pre-inoculated with microbes from southern Wisconsin, the natural heartland of where you live.”

According to the researchers’ findings, trees grown with microbes taken from the coldest locations were at least 50 percent more likely to survive three cold winters at what may be the new, leading edge of climate change.

In the southern location, where trees are likely to be exposed to higher temperatures than they prefer, results were similarly positive for trees matched with climate-informed microbes—although increased resilience was limited to tree species that tended to associate with certain types of microbes, called Arboreal mycorrhizal fungi, which penetrate plant cell walls. Trees subjected to artificial desiccation and paired with imported microbes from the driest conditions received the greatest survival boost, possibly as a result of arboreal fungi’s knack for collecting moisture.

In addition to a better understanding of the way trees and microbes work together in a race against climate change, the syncretism of fungi and plants could be a boon for plans to reforest the planet.

“The number of trees that have been pledged to be planted around the world as part of climate change mitigation strategies is just astronomical,” says Lankao. “Planting trees is one climate change mitigation strategy everyone agrees with, so everyone has a plan to plant billions and trillions of new trees.”

While it doesn’t help mature growth or the next generation of trees with natural seeds, the Lankao lab is enlisting tree nurseries across the Midwest as partners in more microbe-inoculation projects to give new seedlings a leg up.

“We wonder if we can benefit from this study, if it can be used strategically in different regions of the country,” says Lankao. “If we get closer to the tree planting and forest restoration goals set by governments, ideas like this could have a huge impact on the success of those projects.”