Carbon sharing between trees

Carbon sharing between trees

Forest trees are even more interconnected than thought, suggests a new study, which showed that around 40 per cent of the carbon in fine roots of spruce trees came from neighbouring trees.

A chance discovery in a mixed forest in Switzerland reveals that tree-to-tree interaction in forests goes beyond mere competition for resources.

Forest trees are even more interconnected than thought, suggests a new study, which showed that around 40 per cent of the carbon in fine roots of spruce trees came from neighbouring trees. This level of sharing can be crucial for forests, especially under stress conditions like wildfires, say the authors in their paper published in Science recently.

Human-driven activities have been releasing vast amounts of CO2 into the atmosphere since industrialisation began two hundred years ago. Consequently, there is a lot of interest in understanding to what degree forests the largest terrestrial pool of biological carbon, are able to absorb this amount, thereby mitigating climate change, said Tamir Klein who studies eco-physiology at University of Basil, Switzerland, in an email interview sent to me.

While investigating the responses of trees to elevated CO2, Klein and team stumbled upon this discovery. To track the flow of carbon, they had used a tall canopy crane to label five 40-metre-tall Norway spruce trees with stable carbon isotope 13. Five unlabelled spruce trees were used as control. The labelled and unlabelled trees were then measured for C-13 from “tip to toe” - canopy twigs, stems, and fine roots. This was also done for neighbouring unlabelled non-spruce trees. Their methodology ensured no label transfer to other trees. However, the team noticed something unexpected. “We discovered that labelled carbon does find its way to other trees, albeit in the root zone,” said Klein.

In fact, the numbers revealed that roots of neighbouring trees, species no bar, shared an almost similar isotopic signature. The scientists strongly suspect that this interaction is mediated by networks of symbiotic fungi called mycorrhiza which connect the roots of different trees. “Mycorrhizal networks are very common in most forests across biomes and climates. In spruce forests they are so common that they are considered a substantial carbon sink,” said Klein.

Much about the magnitude, direction and the regulation of these transfers is yet unclear. Since all the trees in the study were healthy, and stress-free the authors acknowledged the possibility that the labelled trees were transferring its excess carbon below ground and, in turn, triggering mycorrhizal growth and activity. However, this level of carbon sharing capabilities among neighbouring trees may have implications for forests under stress. “We hypothesise that under stress conditions, trees which are connected to each other through the “right” mycorrhiza species (a multi-host mycorrhiza) might have some advantage over trees which have to withstand as individuals,” said Klein.