Original Paper: Lance, A. C., Carrino-Kyker, S. R., Burke, D. J., & Burns, J. H. (2020). Individual Plant-Soil Feedback Effects Influence Tree Growth and Rhizosphere Fungal Communities in a Temperate Forest Restoration Experiment. Frontiers in Ecology and Evolution, 7(January), 1–12. https://doi.org/10.3389/fevo.2019.00500
Feature Image: By Daniel Wanke
A spoonful of soil isn’t much to look at– until you look closely. With a little magnification, it transforms from being an insignificant piece of earth, to an entire ecosystem unto itself: with invertebrates and tiny worms, and even smaller: the arms of fungi and colonies of bacteria. Having seen the complexity of the soil for themselves, researchers are investigating how soil is shaping landscapes before our eyes.
It makes sense that plants change their soil; their roots dig into the soil and release chemicals that attract hordes of bacteria and fungi. In a sense, the plants’ presence itself will choose which bacteria and fungi are allowed to thrive. But the soil organisms don’t take this all passively– some use their power to cause disease to have control over where plants will successfully grow.
The fact that the plants change the soil community, and also that the soil community changes the plant community, is called plant-soil feedback. I imagine it to be like an animated conversation between plants and soil.
Meet the Neighbors
You’ve probably heard of campaigns to plant millions of trees– a noble effort to restore our forests and fight climate change. But, knowing about plant-soil interactions, what happens when you plant a tree from one place to another? How does a tree respond to those unfamiliar soil microbes?
Planting a tree can be like moving to a new neighborhood. The tree doesn’t know its new microbial neighbors, and that can give the tree a new lease on life: its old soil enemies are nowhere in sight.
This is what led Andrew Lance and his team at Case Western Reserve University to question what happens when you introduce one tree to a different tree’s microbial neighborhood.
To begin, they dug up a circle of soil around red oak trees; a way to get the microbial community that red oaks bring to the soil.
To some of their potted trees of 10 different species, the research team added this red-oak microbial neighborhood, hoping to see how different trees would react to being in their own soil or another species’ soil.
Remembering that some trees benefit from escaping their old microbial neighbors, they thought the trees would do better in soil that’s not theirs. Along with that, maybe if the tree species were more closely related to red oak, the team hypothesized, then those species would grow worse in the red oak’s soil.
The trees stayed there for almost a year and a half, when the researchers checked to see how the plants grew and if the soil community changed. Taking samples of the soils, the researchers analyzed the microbial community with tools much more powerful than a microscope; they used DNA metabarcoding to match the different fragments of DNA to species of fungi. With this, they could see the diversity and composition of the soil fungi.
Different Feedback, Different Trees
In the end, two of their tree species were actually more comfortable in their own soils; bitternut hickory (Carya cordiformis) and burr oak (Quercus macrocarpa) grew better in their own soils than in the red oak-influenced soil.
However, it wasn’t the same story for all the trees. One species, shagbark hickory (Carya ovata) grew better in the red oak-influenced soil. The researchers think this is possibly because the oak and hickory species are often found growing in the same places; their microbial neighbors then are maybe not so different after all, and might facilitate or enhance each of the species growth.
The relatedness of the species wasn’t that important to the tree’s growth– possibly because all the species were closely related. They also found a lot of microbial diversity in all the soils, but it’s hard to say if the differences in the microbial neighborhoods came from the trees themselves, or from other sources like wood chips and nursery soils.
Untangling the links between plants and soil, and the power the soil has over the plant community, is a difficult but worthwhile study. It can help us understand plant pathogens, restore forests, and have some extra wonder when we think of how complex a little dirt can be.