While I was researching nutrient circulation in forests, I came across the mysterious word “fallen roots.” I often hear about fallen leaves, but the expression “roots falling underground” was strange. When I looked it up, I found that the expression “falling off” refers to dead roots being separated from the root. Thin roots with a diameter of less than 2 mm that die and fall off within one to several years are called “fallen roots.” These fallen roots, like fallen leaves, apparently help to nourish the soil and contribute to the material circulation of forests.
https://www.nagoya-u.ac.jp/researchinfo/result/2022/08/post-305.html
First, let’s talk about the role of fallen leaves. From autumn to winter, broadleaf and coniferous trees shed their leaves, and the layer of fallen leaves that accumulates on the soil is where insects hibernate and also increases the soil’s water retention. I guess it’s about retaining heat and water. The finely chopped fallen leaves are further decomposed by soil-dwelling organisms and microorganisms and returned to the soil, providing nutrients to the soil and supporting a rich forest.
https://innosho.co.jp/web-mag-8
Also, in winter, you can see fallen leaves floating down the river, and the nutrients in the leaves are said to circulate back into the river and the sea. In the river, they become a wintering place for fish, and as they flow, they are broken down by river and sea creatures. The property of fallen leaves being able to float in the water makes it possible for them to circulate over long distances. Fallen leaves are amazing.
https://sakana-fuyasu.jp/forest-river.shtml
Speaking of circulation, I’ve been particularly interested in nutrient circulation that defies gravity lately, and I thought that trees might also fit the bill. Trees extend their roots deep into the ground, absorb nutrients from their roots, grow taller, and then shed their leaves from their tall branches. According to a study of tree root depth around the world, the average root depth is about 7m, so I thought that this might be transporting nutrients from underground to the surface. Roots are amazing. Trees are amazing.
https://fores-try.com/forest-research-frontier-2
And it seems that the roots that wither and fall off from these plants continue to be important even after they become fallen roots. They decompose in a similar way to fallen leaves, but their roles are apparently opposite. In the decomposition process, fallen leaves absorb nitrogen and help to nurture many microorganisms, while fallen roots release nitrogen and function as fertilizer. The flow of nitrogen is reversed. It’s also strange that roots before they become fallen roots absorb nitrogen, and release it when they become fallen roots. Fallen roots are amazing.
https://www.ffpri.affrc.go.jp/press/2022/20221025-02/index.html
Among the microorganisms involved in decomposition, there are those that prefer fallen leaves and those that prefer fallen roots. Ecosystems are amazing. And it seems that the nitrogen in the soil reaches the mantle over a long period of time, and then travels to the atmosphere and the surface of the earth via volcanoes. The Earth is an amazing circulation system that combines overlapping small circulations and large circulations.
