Source: Gehring, C.; Sthultz, C.; Flores-Renteria, L.; Whipple, A.; Whitman, T. (2017). Tree genetics defines fungal partner communities that may confer drought tolerance. PNAS, 114 (42), 11169-11174. doi: 10.1073/pnas.1704022114
Why are trees and fungal communities pairing up?
Often trees form important partnerships with fungal communities in the soil. These partnerships can result in trees and plants having better access to water and nutrients. This partnership between trees and fungal communities could help plants survive one of the many consequences of climate change, increased drought. In this study, the researchers focused on the Pinyon pine (Figure 1). The Pinyon pine is found in the southwestern U.S. and is already experiencing large-scale mortality resulting from climate change. The researchers set out to answer three important questions. First, can associations with fungal communities be passed between generations of trees? Second, how do fungal communities impact the growth and survival of the Pinyon pine? After answering these two questions in greenhouse experiments the researchers wanted to know: What happens in the actual environment?
Question 1: Can an association with fungal communities be passed from parental trees to their offspring?
The researchers collected seeds from drought-tolerant and drought-intolerant parent trees and grew them in soil and roots from either drought-tolerant or drought-intolerant trees. After 12 months, samples were collected from the soil of each plant and the fungal community was determined.
The researchers found that seeds from drought-tolerant parents always developed the same fungal community, regardless of if the seeds were grown in soil from drought-tolerant or drought-intolerant trees. This fungal community matched that of the drought-tolerant parents and was different than that of drought-intolerant seeds and parents. This indicated that the association with fungal communities could be passed from parental trees to their offspring.
Question 2: Does the fungal community impact seedling growth during drought?
To determine how the two different fungal communities (those associated with drought-tolerant and drought-intolerant trees) influenced the growth of seeds during drought, the researchers placed a few of each seed type in soil that contained the fungal community, while the others were placed in soil that contained no fungal community. After 7 months of growth under drought conditions, the seedlings were harvested.
The researchers found that the seeds (regardless of parent type) grown in the soil containing the fungal community had more growth than those grown in soil without a fungal community. This indicates that both fungal communities form a mutual relationship with the trees. In other words, both fungal communities (those associated with drought-tolerant and drought-intolerant trees) caused the seeds to grow more than if no fungal community were present. However, seedlings of drought-tolerant parents grew larger than seedlings of drought-intolerant parents. This indicates that the fungal community associated with the drought-tolerant trees is more advantageous than that of the drought-intolerant trees.
Question 3: Does this all happen in real life outside of a greenhouse?
After performing the previous two experiments in a greenhouse, the researchers wanted to know if their findings matched observations made in the field. Yes! The researchers compared the findings from field measurements before and during a drought and found that that presence of the fungal community really improved drought tolerance, even outside of a greenhouse.
The big picture
What can we do now that we know the Pinyon pine and fungal community association can influence the survival of the trees during drought? This information can be important in making decisions related to forest management and restoration. When deciding which portions of forest to preserve or restore, we want to focus on species that are better suited to survive climate change. Think of it this way: Why would we pour economic resources into restoring or preserving trees that will die in a few years because of climate change? It is a waste of time and money. Based on this study, we can now select the trees associated with the key fungal communities that make them more apt to survive drought. In addition, researchers can explore what traits cause the fungal communities to help with drought tolerance and see if they can provide benefits to other trees as well.