Although nitrogen is essential to all living organisms – accounting for 3% of the human body – and 78% of the earth's atmosphere, it is almost ironically difficult for plants and natural systems to access.
Air Nitrogen can not be used directly by most living things. In nature, specialized microbes in soils and waters convert nitrogen into ammonia – an important form of nitrogen that life has easy access to – through a process known as nitrogen fixation. In agriculture, to restore soil fertility, soybeans and other legumes may be planted to facilitate nitrogen fixation.
Another obstacle in providing nitrogen to the plants and ecosystems that rely on them is that microbial nitrogen fixers contain a complex protein called nitrogenase that contains a metal-rich core. Previous research has focused on nitrogenases containing a specific metal, molybdenum.
However, the extremely low level of molybdenum in the soil has raised concerns about the natural limits of land-based nitrogen fixation. Scientists have been wondering what restrictions the lack of molybdenum limits the ability of nature to restore ecosystem fertility as a result of human disturbances, or how humans are increasingly looking for arable land to feed a growing population.
Princeton University researchers have found evidence that other metals can facilitate nitrogen fixation when molybdenum is scarce, suggesting that the process is more resilient than previously thought. This emerges from a study published in the journal Proceedings of the National Academy of Sciences . In a 600 kilometer area of the Canadian boreal forest, the researchers found that ecosystem-scale nitrogen fixation can also be catalyzed by the metal vanadium, especially in northern regions with limited natural nitrogen input.
The work is fundamentally revising our understanding of how micronutrients control nitrogen status and ecosystem fertility, "said senior author Xinning Zhang, Assistant Professor of Earth Sciences and Princeton Environmental Institute.
Related to nutrient budgets, cycling and health Biodiversity, "she said. "One consequence of this finding is that the current estimates of nitrogen input into boreal forests can be significantly underestimated by fixation, which is an important issue in our understanding of the nutrient needs for forest ecosystems that currently function as an important sink for anthropogens carbon."  First author Romain Darnajoux, a postdoctoral researcher in Zhang's research group, said the findings confirm a long-standing hypothesis in the scientific community that various metal variants of nitrogenase exist to allow organisms to deal with changes in metal availability. The researchers found that vanadium-based nitrogen fixation plays a key role only in the presence of low levels of molybdenum in the environment.
"It seems that nature has developed backup methods to maintain the fertility of the ecosystem in a variable environment," said Darnajoux. "Each nitrogen cycling step involves an enzyme that requires certain trace metals, and molybdenum and iron are generally the focus of scientific research because they are considered essential for the nitrogen-fixing enzyme nitrogenase, but it is also a vanadium-based nitrogenase." but the nitrogen input by this enzyme was unfortunately largely ignored.
Darnajoux and Zhang worked with Nicolas Magain and François Lutzoni at Duke University and Marie Renaudin and Jean-Philippe Bellenger at the University of Sherbrooke in Quebec.  The researchers' findings suggest that current estimates of nitrogen input in boreal forests due to fixation are extremely low, which would underestimate the nitrogen requirements for robust plant growth, said Darnajoux Boreal forests help mitigate climate change by acting as a sink for anthropogenic carbon, although not so many in these northern forests as in the most sparsely populated metropolis, human activities can significantly affect the fertility of forests through the atmospheric transport of air pollution laden with nitrogen and metals such as molybdenum and vanadium.
"Human activities that significantly alter air quality These can have a profound impact on how remote ecosystems work, "Zhang said. "The findings underscore the importance of air pollution for changing micronutrient and macronutrient dynamics, and as air is a global phenomenon, the relationship between the metal and nitrogen cycle and air pollution has some interesting political and management dimensions."
The researchers' findings may help develop more accurate climate models that do not provide explicit information on molybdenum or vanadium in global nitrogen, land, ocean, and atmosphere simulations of global nitrogen flux.
Importance of Vanadium-Driven Nitrogen Binding Places Another High Importance Darnajoux and Zhang said latitude and temperate and tropical systems are the most likely. The threshold amount of molybdenum needed by an ecosystem to activate or deactivate vanadium-nitrogen fixation was remarkably similar to the molybdenum requirement for nitrogen fixation found on samples with different biomass.
Researchers will continue the search for nitrogen-based vanadium in the northern latitudes. They have also focused on areas closer to home, and have initiated studies on micro- and macronutrient dynamics in temperate New Jersey forests. They plan to extend their work to tropical systems.
The publication "Molybdenum Threshold for the Ecosystem" Alternative Vanadium Nitrogenase Activity in Boreal Forests ", published by the Proceedings of the National Academy of Science online in the run-up to printing on November 11.
Research shows ways to improve nitrogen production in legumes
Romain Darnajoux el al., "Molybdenum Threshold for the Activity of Alternative Vanadium Nitrogenases on the Ecosystem Scale in Boreal Forests", PNAS (2019). www.pnas.org/cgi/doi/10.1073/pnas.1913314116
Researchers find nature's conservation plan for converting nitrogen into plant nutrients (2019, November 11)
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