Buried scanners reveal hidden rhythms beneath the forest

Researchers from the University of Tartu buried ordinary scanners in waterproof boxes beneath the soil of Järvselja forest to monitor the hidden ecosystem in real time, ERR reported. The method revealed previously unseen underground rhythms and linked them to processes visible above ground.

Scientists had traditionally studied root systems by digging them up, a process that inevitably destroyed the delicate network they were trying to analyse. “Serious root science began more than 100 years ago. Until the end of the last century, it mostly involved excavation — we destroyed the system in order to analyse, study or measure the roots,” said Ivika Ostonen, a professor of root ecology at the University of Tartu, on the programme Ökoskoop.

The soil beneath the forest contains extensive biodiversity on which trees and other plants depend. In one square metre of boreal forest, there are about 20 metres of thick roots, 20 kilometres of fine roots and up to one million kilometres of fungal hyphae, Ostonen said. Together, they sustain the food chain and biodiversity of soil life, much of which remains unknown.

An engineer who joined the research team built waterproof boxes for the equipment, allowing the scientists to launch their first pilot project that same spring. Cameras installed in the soil took thousands of images of their surroundings at hourly intervals.

The researchers compiled the photographs into time-lapse videos showing fungal threads growing and tiny mites moving through the soil. They also observed when roots with different functions were active and how water flowed through the soil after rain.

“When we introduced this method, I felt during the first few months that I had learned more than in the previous 20 years, during which I had dug up roots, examined them under a microscope, cleaned and measured them. It was a eureka moment,” Ostonen said.

Early experiments revealed a daily growth cycle in the growth roots of Norway spruce. A master’s student who divided the day into four periods found that the spruce roots slowed their growth from midday until 6 p.m.

The rhythm helped researchers connect underground activity with what was happening in the tree canopy. During the same afternoon period, the tree’s above-ground pores close, for example on very hot days, to prevent water loss.

“This is the first point at which we can begin combining above-ground ecophysiological measurements with underground ones, something that has not been possible until now,” Ostonen said.