Dr. Christine Jurasinski LabLearner Staff Scientist
What images does the word “fungi” bring to mind? Well, chances are they’re not images of weathering or erosion. Yet, a recent discovery by researchers in Great Britain has shown that fungi play a significant role in the erosion process.
For years, scientists have known that the roots of plants and trees contribute to the erosion of rock. Ask a 6th grade LabLearner student about the causes of erosion and weathering of rocks, and tree roots are likely to be one of their answers. However, unlike the answer to “what is a cause,” the answer to “HOW do roots cause erosion” was not known. That is, until recently.
Dr. Bonneville and colleagues from Leeds University in Great Britain set out to answer this question. They investigated the erosion of rocks by plants on a nanoscale. Remember, that the prefix “nano” means one billionth of something, so the events and processes they investigated were not something that could be seen by the human eye or even a compound microscope. When analyzing their results, they used an electron microscope to view changes in rocks. What they found was that fungi on the roots of trees caused the physical and chemical breakdown of rocks, something long hypothesized, but never shown.
So, what exactly happens on the nanoscale when plant roots invade a rock? First, it’s important to remember that almost all plants, including trees, have fungi called mycorrhiza that grow on their roots. Dr. Bonneville and his colleagues created an experiment that modeled this. They obtained a pine tree seedling with mycorrhiza on its roots and placed it in a transparent pot containing nutrient-poor soil and a specific kind of mineral called biotite. Biotite is a mineral commonly found in rock and it is rich in potassium, iron and magnesium. No other fungi or microorganisms were in the soil or on the roots. Then the researchers waited three months. After three months they examined the biotite along a single root using an electron microscope. They found that the biotite at the tip was bent as a result of mechanical pressure from the fungi, a pressure that can reach as high as the pressure in a car tire. This pressure if you think about it, is pretty amazing since the mycorrhiza are microscopic organisms. After performing other tests, they found that the fungi had also chemically altered the biotite, removing its potassium and causing the break-down of the biotite into other soil minerals, vermiculite and ferrihydrate.
Their results suggest that at the nanoscale, tree and plants roots cause erosion of rock through both physical and chemical means. The fungi bend and weaken the crystal structure of rock first and then chemically alter its composition by removing potassium. In addition, the wedging and bending of the biotite’s crystal structure allows other iron compounds in the rock to chemically react with oxygen in the air. In the end, the potassium and other released nutrients are passed onto the roots of the trees or plants and the area around the root that was once rock becomes soil.
For LabLearner students these experiments bridge some of the concepts they learn in the Weathering and Erosion CELL and the Classification GAP Unit. In the Weathering and Erosion CELL, students investigate differences between physical and chemical weathering and erosion of rocks. In doing so, they learn that in nature both types of weathering and erosion occur and that physical weathering and erosion aids chemical weathering and erosion by first breaking down rock into smaller pieces that can be more systemically “attacked” by chemicals. In the Classification GAP Unit, students learn about various multi-cellular organisms, one of which is fungi. They also learn about some properties that are characteristic of fungi, including a symbiotic relationship with other organisms such as plants, and the secretion of enzymes that breakdown matter in their environment.
In the past, students may not have linked the concepts described above together. This latest research, however, illustrates once again that LabLearner students will benefit from exploring all areas of science and hopefully finding new and intriguing connections between them.
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