Science Snippets: Linking Plants with Soil

Draft script:

We all know what comprises a weed. A weed is simply a plant out of place. When a plant appears where it is unwanted, we call it a weed. Similarly, dirt is soil out of place. When soil shows up where it is unwanted, it’s called dirt.

Anthropogenic climate change is making it difficult for plants to survive. In addition, plants cannot simply move from one warm place to another. Plants are inextricably tied to soils and the microorganisms within soils. An example comes from Science Magazine on 27 May 2024 with a story titled Climate change is moving tree populations away from the soil fungi that sustain them. The story begins with a good overview of the situation: “As our planet warms, many species are shifting to different locations as their historical habitats become inhospitable. Trees are no exception – many species’ normal ranges are no longer conducive to their health, but their shift to new areas that could better sustain them has been lagging behind those of other plants and animals. Now, scientists show that the reason for this lag might be found belowground. A study published in … [Proceedings of the National Academy of Sciences on 28 May 2024] shows that trees, especially those in the far north, may be relocating to soils that don’t have the fungal life to support them.” I’ll have more from the renowned peer-reviewed journal article later. The article at Science Magazine continues: “Most plants form belowground partnerships with mycorrhizal fungi, microscopic, filamentous fungi that grow in the soil and connect with plant roots to supply plants with critical nutrients in exchange for carbon. Most large coniferous trees in northern latitudes form relationships with a kind of mycorrhizal fungi called ectomycorrhizal fungi.” That’s correct: Most plants form relationships with other organisms as a means of survival.

Two paragraphs later, we read: “The trees most at risk of this climate mismatch in North America are those in the pine family, find the authors. Areas of particular concern are the edges of species ranges where trees often face the harshest conditions. Here, the authors discovered that trees with higher survival rate in these locations have more diverse mycorrhizal fungi, a sign that these symbioses may be critical for helping trees withstand the effects of climate change.”

The first author of the peer-reviewed paper in the Proceedings of the National Academy of Sciences provides the bottom line when he is quoted in the article in Science Magazine: “It’s absolutely vital that we continue to work to understand how climate change is affecting mycorrhizal symbioses. These relationships underpin all life on Earth – it’s critical that we understand and protect them.”

In other words, the small things matter. Fungi in the soil are critical to the continued survival of trees.

The peer-reviewed, open-access article in the Proceedings of the National Academy of Sciences is authored by five scholars. Published 28 May 2024, it is titled Climate mismatches with ectomycorrhizal fungi contribute to migration lag in North American tree range shifts.

The peer-reviewed paper opens with a section titled Significance, where we find this information: “Predicting where climate change might disrupt species interactions is critical to protect against biodiversity loss and maintain ecosystem functioning. This is particularly true for tree symbioses with ectomycorrhizal fungi …, which are widespread and regulate key aspects of forest productivity, species composition, and nutrient cycling. Here, we assess the risk of climate change to overlapping habitat suitability of tree species and their … [ectomycorrhizal fungi] partners across North American forest ecosystems. Our results show that climate change will negatively impact 35% of tree-[ectomycorrhizal fungi] … partnerships by shrinking their shared habitat conditions. We also find that tree migration lag is linked to reduced diversity of [ectomycorrhizal fungi] … partners, indicating that symbiotic disequilibrium is a challenge facing tree species responses to climate change.”

In other words, it’s not only anthropogenic climate change that poses a challenge to plants. It’s also the relationship between and among organisms. Even if we were able to solve the climate-change disaster we have collectively created, we still wouldn’t be out of the proverbial woods. The long Abstract explains: “Climate change will likely shift plant and microbial distributions, creating geographic mismatches between plant hosts and essential microbial symbionts (e.g., ectomycorrhizal fungi, …). The loss of historical interactions, or the gain of novel associations, can have important consequences for biodiversity, ecosystem processes, and plant migration potential, yet few analyses exist that measure where mycorrhizal symbioses could be lost or gained across landscapes. Here, we examine climate change impacts on tree-[ectomycorrhizal fungi] … codistributions at the continent scale. We built species distribution models for 400 [ectomycorrhizal fungi] … species and 50 tree species, integrating fungal sequencing data from North American forest ecosystems with tree species occurrence records and long-term forest inventory data. Our results show the following: 1) tree and [ectomycorrhizal fungi] … climate suitability to shift toward higher latitudes; 2) climate shifts increase the size of shared tree-[ectomycorrhizal fungi] … habitat overall, but 35% of tree-[ectomycorrhizal fungi] … pairs are at risk of declining habitat overlap; 3) climate mismatches between trees and [ectomycorrhizal fungi] … are projected to be greater at northern vs. southern boundaries; and 4) tree migration lag is correlated with lower richness of climatically suitable [ectomycorrhizal fungi] … partners. This work represents a concentrated effort to quantify the spatial extent and location of tree-[ectomycorrhizal fungi] … climate envelope mismatches. Our findings also support a biotic mechanism partially explaining the failure of northward tree species migrations with climate change: reduced diversity of co-occurring and climate-compatible symbionts at higher latitudes. We highlight the conservation implications for identifying areas where tree and [ectomycorrhizal fungi] … responses to climate change may be highly divergent.”

The bottom line comes in the final two sentences of the Discussion subsection of the peer-reviewed paper: “While more empirical work on this topic is certainly warranted, it may help explain previous observations of migration failure among a wide range of North American tree species ... Consequently, our findings suggest that mycorrhizal fungi will need to be carefully considered as part of any assisted migration strategies for North American tree species.”

The situation is messier than we thought. We cannot simply move trees from one location to another as the climate changes. We need to move tiny soil organisms, too. Planting trees is difficult enough. Creating environments suitable for the survival of trees is an enormous challenge.