Nitrogen-fixing trees "eat" rocks and play a vital role in forest health

The study published today in the journal Proceedings of the National Academy of Sciences.

Researchers at Oregon State University and the US Geological Survey have determined that red alder, thanks to its symbiotic relationship with nitrogen-fixing bacteria, draws in nutrients blocked in the bedrock, such as calcium and calcium. phosphorus. This process accelerates the dissolution of the rock, releasing more mineral nutrients allowing plants and trees to grow.

The study addresses the long-term implications of how nutrients are found in ecosystems, supporting their long-term growth and productivity, and ultimately carbon storage, said geochemist Julie Pett-Ridge. at the College of Agricultural Sciences of OSU and co-author. on the study.

The research also helps to better understand a specific set of trees known for their ability to naturally fertilize forests by converting atmospheric nitrogen to forms available for other plants. This process, called fixing nitrogen, is essential for natural ecosystems.

"Nitrogen comes mainly from the atmosphere, but more than 20 other nutrients come mostly from rock," said Pett-Ridge. "We have established a link between these two processes.Nitrogen-fixing trees, which we knew were special for their nitrogen supply from the atmosphere, also have a unique ability to accelerate the process. Supply of nutrients derived from rocks. "

Red Alder is a deciduous broadleaf tree native to western North America. It is closely related to other alder species in the world. Like all alder species, red alder can release nitrogen into the soil through nodules on its roots.

In a way, the red alder "eats" stones, said Steven Perakis, a USGS ecologist and senior author of the study funded by the National Science Foundation.

"These trees can not only add nitrogen to ecosystems, they can also add all the other nutrients needed for forests to grow and store carbon," Perakis said. "This knowledge can contribute to the sustainability of forest practices in managed forests." Farmers have long understood that nutrients are essential to maintaining productivity, and these processes take a little longer to take place in forests. "

Nitrogen is the most important nutrient for plant life. But atmospheric nitrogen is useless unless its chemical bond is degraded by bacteria. Some tree species, such as red alder, have created a symbiotic relationship with nitrogen – fixing bacteria. Bacteria have an enzyme that converts atmospheric nitrogen to ammonia, which promotes plant growth.

In this study, Pett – Ridge and Perakis examined six different tree species growing in the Tillamook State Forest in the Oregon Coast Range: Sitka spruce, Douglas fir, Hemlock, and Douglas fir. Western, western cedar, bigleaf maple and red alder.

They collected leaves to analyze their composition in isotopes of strontium, which reveals the nutrient sources of the trees. They determined that red alder leaves showed a stronger fingerprint of nutrients derived from rock than other trees.

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More information:
Steven S. Perakis et al., "Nitrogen-fixing red alders tap into nutrients derived from rocks" PNAS (2019). www.pnas.org/cgi/doi/10.1073/pnas.1814782116