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Mystery unearthed: How do trees of different species transfer carbon between each other?

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According to Israeli scientists from the Weizmann Institute of Science, trees use an intricate networks of fungi to transfer carbon, minerals, nutrients and water between their roots

By ILANIT CHERNICK

In a fascinating discovery, Israeli scientists from Rehovot’s Weizmann Institute of Science recently unearthed how trees of different species transfer carbon between each other using underground fungal networks.

According to Dr. Tamir Klein and PhD student Ido Rog of the Plant and Environmental Sciences Department there are intricate networks of fungi that connect the roots of different tree species with one another. 

“These networks enable the trees to exchange minerals, nutrients, water and carbon, while funneling carbon to the fungi in return,” the scientists explained in a press release. 

Although symbiotic relationships between trees and fungi have been known for decades, “this is the first time that different tree species have been observed cooperating with one another using an underground network of fungi in their natural setting. 

“The findings add evidence to the trend that is forcing ecologists to shift their thinking about how carbon transfer gets controlled within the forest,” they added.

Klein pointed out that the fact that trees are “’sharing their wealth’ across species, suggests that there is some sort of ‘hidden’ management occurring.

“We think the management is dominated by the fungi,” he continued. “Fungi need to secure their own carbon sources; it is in their best interest to ensure that all the trees within the network are healthy and strong.”

Addressing what inspired the research Klein said it was his research during his stint as a postdoctoral fellow in Switzerland “that laid the groundwork… for this current discovery.” 

Initially, Klein had set his sights 40 meters above the ground for his research, using a construction crane to install measuring instruments above the forest canopy. 

During these experiments, Klein found that carbon was being transferred between neighboring mature trees of different species, including spruce, pine, birch and larch. 

But, he said, the measurements did not add up. The trees had stored more carbon than he could account for by balancing carbon emission and intake measurements at the canopy.  

This fungus growing in a mixed forest plot near Beit- Shemesh, Israel, plays a role in carbon transfer in the forest network
(Pictures Credit: Weizmann Institute of Science)

This was when Rog joined forces with Klein to solve this mystery and track down the missing component of the carbon sink. 

For over four years Rog has been painstakingly digging through rock-laden soil, excavating fine roots and carefully following them through the terrain to identify their parent trees. 

The duo then installed devices deep underground and afterwards employed next-generation sequencing techniques. 

Rog analyzed over 1,000 root tips from 12 individuals of four tree species including spruce, pine, larch and beech. 

Not only was the scientist able to quantify the amount of carbon being transferred between the trees, but he also identified the fungal species responsible – “ectomycorrhizal”  or symbiotic fungi. 

This specific fungi, the scientists said, is known for their special relationships with trees, and thus their importance in the web of forest ecology has long been recognized, but no one had yet imagined that trees use them as conduits for carbon sharing.

“Out of the fungal species sampled, we identified at least eight different species that are generalists and common to the four tree species we analyzed; 90% of them are associated with at least two host species,” Rog explained. “We also found that trees that were more closely related, such as spruce and pine, had a more similar mix of fungal species connected to their root tips and shared more carbon between them than the more distantly-related species, say larch and beech.” 

But overall, Rog stressed, carbon was found to be exchanged between all species.

“If the fungi are running the show, they could be directing resources between trees depending on their specific needs,” Klein added.

From the trees’ point of view, carbon sharing would logically occur only between trees of the same species, giving them an evolutionary advantage over other species. This suggests that forest evolution may be taking place on a different level than simple tree kinship.

To test their hypothesis, the scientists have been conducting similar studies in Israeli forests with a particular focus on the carob tree, which has leaves that stay a luscious, shiny green even in extremely hot, dry conditions. 

“According to historical and biblical legends, the carob tree has ‘mysterious powers’ – secret ways of surviving in semi-arid climates,” Rog said, wondering if “perhaps fungi were the secret.  The scientists found that when carob trees are planted in a mixed forest of oak, conifer and pine, they also become part of the fungal network. 

The researchers are now beginning to uncover the specific species of fungi that connect the carobs to other tree species.

The duo pointed out that this fungus is currently growing in a mixed forest plot near the Israeli city of Beit Shemesh, plays a role in carbon transfer in the forest network

“If the fungi are running the show, they could be directing resources between trees depending on their specific needs,” Klein explained. “On a theoretical level, our findings are altering our understanding of forest ecology, and scientists are beginning to realize that trees are more collaborative than previously believed.

He pointed out that the fungi’s actions would be especially advantageous if a forest is subjected to such stressors as climate change, drought, fire or disease, adding that “the result would be a more resilient forest.”

The scientists said that they are also planning another experiment to induce conditions of drought in a small area in hopes of investigating the role of the fungi in the forest system when it is confronted with an ecological disturbance. 

Klein concluded that they are working with the Keren Kayemet LeYisrael – Jewish National Fund “to encourage the mixing of tree species in Israel’s forests in order to build greater ecological resilience and stability.”

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