CORVALLIS, Ore. — Red alder trees play a critical role in maintaining healthy forest ecosystems by helping release essential nutrients from bedrock, according to new research from Oregon State University and the U.S. Geological Survey.
The study adds to scientists’ understanding of how nitrogen-fixing trees help fertilize forests and influence carbon storage.
The findings were published in Proceedings of the National Academy of Sciences and highlight the long-term importance of how nutrients enter and sustain ecosystems.
Researchers found that red alder, through a symbiotic relationship with nitrogen-fixing bacteria in its root nodules, is able to extract nutrients such as calcium and phosphorus from bedrock. The process accelerates the weathering of rock, releasing mineral nutrients that are vital for plant and tree growth.
“Nitrogen mostly comes from the atmosphere, but more than 20 other nutrients mostly come from rock,” said Julie Pett-Ridge, a geochemist and professor in Oregon State’s College of Agricultural Sciences and co-author of the study. “We’ve established a connection between those two processes. Nitrogen-fixing trees, which we knew were special for bringing in nitrogen from the atmosphere, also have a unique ability to accelerate the supply of rock-derived nutrients.”
The study adds to scientists’ understanding of how nitrogen-fixing trees help fertilize forests and influence carbon storage. Red alder is known for its ability to convert atmospheric nitrogen into forms other plants can use — a process called nitrogen fixation.
“Nitrogen is the most important nutrient for plant life, but atmospheric nitrogen isn’t usable unless bacteria break its chemical bonds,” Pett-Ridge explained. “Some trees, like red alder, form relationships with bacteria that perform this conversion, providing a natural source of nitrogen.”
The new study reveals that red alder also enhances access to other nutrients typically locked in bedrock — nutrients essential for long-term forest productivity and carbon storage.
“In a way, red alder ‘eats’ rocks,” said lead author Steven Perakis, a research ecologist with the USGS Forest and Rangeland Science Center in Corvallis and courtesy faculty member in Oregon State’s College of Forestry. “These trees not only can add nitrogen to ecosystems, they also can add all the other nutrients that forests require to grow and store carbon.”
Isotope analysis reveals nutrient origins
To compare how different tree species access nutrients, the researchers studied six species in the Tillamook State Forest in Oregon’s Coast Range: Sitka spruce, Douglas-fir, western hemlock, western redcedar, bigleaf maple and red alder.
The team collected leaves from each tree species and analyzed their strontium isotope composition in Oregon State’s W. M. Keck Collaboratory for Plasma Spectrometry. Isotope fingerprints indicate whether nutrients come from atmospheric or rock sources.
The results showed that red alder leaves had the strongest signal of rock-derived nutrients, compared with the other five species.
Implications for sustainable forest management
Perakis noted that understanding how red alder enhances nutrient cycling can inform sustainable forest practices.
“Farmers figured out long ago that nutrients are essential for maintaining productivity,” he said. “In forests, these processes take longer to reveal themselves, but they are just as important.”
By improving access to both atmospheric and rock-derived nutrients, red alder helps support long-term forest health, productivity and carbon storage — key components in mitigating climate change and managing natural ecosystems.
Previously titled Nitrogen-fixing trees “eat” rocks, play pivotal role in forest health
