Although nitrogen is essential for all living organisms – it makes up 3% of the human body – and makes up 78% of the Earth's atmosphere, it is almost ironically difficult to access plants and natural systems.
Atmospheric nitrogen is not directly applicable to most living things. In nature, specialized microbes in soil and water bodies convert nitrogen into ammonia – a key form of nitrogen that life can easily access – through a process called nitrogen fixation. In agriculture, soybeans and other legumes can be planted to facilitate nitrogen fixation to restore soil fertility.
An additional obstacle in the process of making nitrogen available to plants and ecosystems that rely on it is that microbial nitrogen "fixers" incorporate a complex protein called nitrogen, containing a metal-rich core. Existing research has focused on nitrogen containing a specific metal, molybdenum.
However, the extremely small amount of molybdenum found in the soil has raised concerns about the natural limits of nitrogen fixation on land. Scientists have been wondering what limits the deficiencies of molybdenum sites to nature's capacity to restore ecosystem fertility in the face of human disturbances or as people increasingly demand arable land to feed a growing population.
Researchers at Princeton University have found evidence that other metals can facilitate nitrogen fixation when molybdenum is depleted, suggesting that this process may be more resistant than previously thought, according to a study published in the journal Proceedings of the National Academy of Sciences. Working across a forest width 600 kilometers from a Canadian rain forest, the researchers found that nitrogen fixation on an ecosystem scale could also be catalyzed by metallic vanadium, especially in northern regions with limited natural nitrogen inputs.
"This work prompts a major overhaul of our understanding of how micronutrients control the nitrogen and fertility status of the nitrogen allotystem," said senior author Xining Angang, assistant professor of geosciences and Princeton Institute of the Environment.
"We need to know more about how nitrogen fixation is manifested in nutrient budgets, cycling and biodiversity," she said. "One consequence of this finding is that current estimates of the amount of nitrogen entry into boreal forests by fixation can be significantly underestimated. This is a major issue for our understanding of the nutritional requirements for forest ecosystems, which currently function as an important anthropogenic sink. carbon. "
The first author Roman Darnaijuks, a postdoctoral research fellow at the ang group, explained that the findings confirm the long-standing hypothesis in the scientific community that there are different metallic variants of nitrogen so that organisms can cope with changes in metal availability. Researchers have found that vanadium-based nitrogen fixation is significant only when the environmental level of molybdenum is low.
"It seems that nature has developed back-up methods to maintain the ecosystem's fertility when the environment is changing," Darnajuks said. "Every step in the nitrogen cycle involves an enzyme that needs specific metals to work with. Molybdenum and iron are usually the focus of a scientific study because they are considered essential in the nitrogen kits for nitrogen. However, vanadium-based nitrogen also exists. but the nitrogen intake of this enzyme is unfortunately largely ignored. "
Darnayux and Ang have worked with Nicholas Magain and Frank Ozacon at Duke University and Marie Renaudin and Jean-Philippe Belanger at the University of Quebec in Cherbourg.
Researchers suggest that current estimates of nitrogen intake in rainforest through fixation are poorly low, which would underestimate the demand for stable plant growth nitrogen, Darnajuks said. Borial forests help mitigate climate change by acting as a sink for anthropogenic carbon. Although these northern forests do not see so many human visitors, even the lightest populated metropolis, human activities can still have the greatest impact on the fertility of forests through atmospheric transport of nitrogen-laden air pollution and metals such as molybdenum and vanadium.
"Human activities that significantly change air quality can have a far-reaching impact on how even remote ecosystems work," Angang said. "The findings emphasize the importance of air pollution in changing micronutrients and macronutrient dynamics. Since air is a global community, the link between metals and the nitrogen cycle and air pollution has interesting policy and management dimensions. "
The researchers' findings could help develop more accurate climate models, which do not contain explicit information on molybdenum or vanadium for simulations of global nitrogen flow through the land, ocean and atmosphere.
The importance of vanadium-driven nitrogen fixation extends to other high-latitude regions and most likely to temperate and tropical systems, say Darnayux and Ang. The ecosystem molybdenum content threshold to be activated or deactivated by nitrogen fixation The nitrogen they found in their study was remarkably similar to the molybdenum nitrogen fixation requirements found for specimens considering diverse biomes.
The researchers will continue the search for vanadium-based nitrogen fixation in the northern latitudes. They have also turned their eyes to areas closer to home, initiating studies of micro- and macronutrient dynamics in temperate forests in New Jersey and plan to expand their work into tropical systems.
The paper, "Molybdenum Threshold for Alternative Vanadium Nitrogen Activity in Forest Ecosystems," was published by Proceedings of the National Academy of Sciences front-to-front printing on November 11th.
Research reveals ways to improve nitrogen production in legumes
Roman Darnaijuks el., "Molybdenum Threshold for Alternative Vanadium Nitrogen Scale Ecosystem Activity in Aboriginal Forests," PNAS (2019). www.pnas.org/cgi/doi/10.1073/pnas.1913314116
Researchers unveil nature's backup plan to convert nitrogen into plant nutrients (2019, November 11)
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