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plant science

Dec 06
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Marie Renaudin, University of Sherbrooke

Researchers find nature’s backup plan for converting nitrogen into plant nutrients

By News, Plant Science

Although nitrogen is essential for all living organisms — it makes up 3% of the human body — and comprises 78% of Earth’s atmosphere, it’s almost ironically difficult for plants and natural systems to access it. 

Atmospheric nitrogen is not directly usable by most living things. In nature, specialized microbes in soils and bodies of water convert nitrogen into ammonia — a crucial form of nitrogen that life can easily access — through a process called nitrogen fixation. In agriculture, soybeans and other legumes that facilitate nitrogen fixation can be planted to restore soil fertility. 

An additional obstacle in the process of making nitrogen available to the plants and ecosystems that rely on it is that microbial nitrogen “fixers” incorporate a complex protein called nitrogenase that contains a metal-rich core. Existing research has focused on nitrogenases containing a specific metal, molybdenum. 

The extremely small amount of molybdenum found in soil, however, has raised concerns about the natural limits of nitrogen fixation on land. Scientists have wondered what restrictions the scarcity of molybdenum places on nature’s capacity to restore ecosystem fertility in the wake of human-made disturbances, or as people increasingly search for arable land to feed a growing population. 

Princeton University researchers have found evidence that nitrogen fixation can be facilitated by metals that are more abundant in soil, which suggests that nitrogen fixation may be more resilient to molybdenum scarcity than previously thought, according to a study published in the journal Proceedings of the National Academy of Science. Working in a 372 mile (600 kilometer) stretch of boreal forest in Canada, the researchers found that nitrogen fixation at an ecosystem scale can also be catalyzed by the metal vanadium, particularly in northern regions with limited natural nitrogen inputs.

“This work prompts a major revision of our understanding of how micronutrients control ecosystem nitrogen status and fertility,” said senior author Xinning Zhang, assistant professor of geosciences and the Princeton Environmental Institute. 

“We need to know more about how nitrogen fixation manifests in terms of nutrient budgets, cycling and biodiversity,” she said. “One consequence of this finding is that current estimates of the amount of nitrogen input into boreal forests through fixation may be significantly underestimated. This is a major issue for our understanding of nutrient requirements for forest ecosystems, which currently function as an important sink for anthropogenic carbon.”

First author Romain Darnajoux, a postdoctoral research associate in Zhang’s research group, explained that the findings validate a long-held hypothesis in the scientific community that different metal variants of nitrogenase exist so that organisms can cope with changes in metal availability. The researchers found that vanadium-based nitrogen fixation was only substantive when environmental molybdenum levels were low.

“It would seem that nature evolved backup methods to sustain ecosystem fertility when the environment is variable,” Darnajoux said. “Every nitrogen-cycle step involves an enzyme that requires particular trace metals to work. Molybdenum and iron are typically the focus of scientific study because they’re considered to be essential in the nitrogen-fixing enzyme nitrogenase. However, a vanadium-based nitrogenase also exists, but nitrogen input by this enzyme has been 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 Québec.

The researchers’ results suggest that the current estimates of nitrogen input into boreal forests through fixation are woefully low, which would underestimate the nitrogen demand for robust plant growth, Darnajoux said. Boreal forests help mitigate climate change by acting as a sink for anthropogenic carbon. Though these northern forests do not see as many human visitors as even the most lightly populated metropolis, human activities can still have major impacts on forest fertility through the atmospheric transport of air pollution loaded with nitrogen and metals such as molybdenum and vanadium. 

“Human activities that substantially change air quality can have a far-reaching influence on how even remote ecosystems function,” Zhang said. “The findings highlight the importance of air pollution in altering micronutrient and macronutrient dynamics. Because air is a global commons, the connection between metals and nitrogen cycling and air pollution has some interesting policy and management dimensions.”

The researchers’ findings could help in the development of more accurate climate models, which do not explicitly contain information on molybdenum or vanadium in simulations of the global flow of nitrogen 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, Darnajoux and Zhang said. The threshold for the amount of molybdenum an ecosystem needs to activate or deactivate vanadium nitrogen fixation that they found in their study was remarkably similar to the molybdenum requirements of nitrogen fixation found for samples spanning diverse biomes. 

The researchers will continue the search for vanadium-based nitrogen fixation in the northern latitudes. They’ve also turned their eyes toward areas closer to home, initiating studies of micro- and macronutrient dynamics in temperate forests in New Jersey, and they plan to expand their work to tropical systems.

Read the paper: Proceedings of the National Academy of Science

Article source: Princeton University

Author: Joseph Albanese

Image credit: Marie Renaudin, University of Sherbrooke

Nov 14
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Communicating uncertainty about climate change

By Climate change, News, Science communication

The ways climate scientists explain their predictions about the impact of global warming can either promote or limit their persuasiveness.

The more specific climate scientists are about the uncertainties of global warming, the more the American public trusts their predictions, according to new research by Stanford scholars.

But scientists may want to tread carefully when talking about their predictions, the researchers say, because that trust falters when scientists acknowledge that other unknown factors could come into play.

In a study in Nature Climate Change, researchers examined how Americans respond to climate scientists’ predictions about sea level rise. They found that when climate scientists include best-case and worst-case case scenarios in their statements, the American public is more trusting and accepting of their statements. But those messages may backfire when scientists also acknowledge they do not know exactly how climate change will unfold.

“Scientists who acknowledge that their predictions of the future cannot be exactly precise and instead acknowledge a likely range of possible futures may bolster their credibility and increase acceptance of their findings by non-experts,” said Jon Krosnick, a Stanford professor of communication and of political science and a co-author on the paper. “But these gains may be nullified when scientists acknowledge that no matter how confidently they can make predictions about some specific change in the future, the full extent of the consequences of those predictions cannot be quantified.”

Effects of communicating uncertainty

Predicting the future always comes with uncertainty, and climate scientists routinely recognize limitations in their predictions, note the researchers.

“In the context of global warming specifically, scientific uncertainty has been of great interest, in part because of concerted efforts by so-called ‘merchants of doubt’ to minimize public concern about the issue by explicitly labeling the science as ‘uncertain,’” said Lauren Howe, who was a postdoctoral scholar at Stanford when she conducted the research with Krosnick and is first author on the paper.

“We thought that, especially in this critical context, it was important to understand whether expressing uncertainty would undermine persuasion, or whether the general public might instead recognize that the study of the future has to involve uncertainty and trust predictions where that uncertainty is openly acknowledged more than those where it is minimized,”

Howe said.

To better understand how the public reacts to scientists’ messages about the uncertainties of climate change, the researchers presented a nationally representative sample of 1,174 American adults with a scientific statement about anticipated sea level rise.

Respondents were randomly assigned to read either a prediction of the most likely amount of future sea level rise; a prediction plus a worst-case scenario; or a robust prediction with worst-case and best-case scenarios, for example: “Scientists believe that, during the next 100 years, global warming will cause the surface of the oceans around the world to rise about 4 feet. However, sea level could rise as little as 1 foot, or it could rise by as much as 7 feet.”

The researchers found that when predictions included a best-case and worst-case scenario, it increased the number of participants who reported high trust in scientists by 7.9 percentage points compared with participants who only read a most likely estimate of sea level rise.

Changes in environmental policies, human activities, new technologies and natural disasters make it difficult for climate scientists to quantify the long-term impact of a specific change – which scientists often acknowledge in their predictions, the researchers said. They wanted to know if providing such well-intended, additional context and acknowledging complete uncertainty would help or hurt public confidence in scientific findings.

To find out, the researchers asked half of their respondents to read a second statement acknowledging that the full extent of likely future damage of sea level rise cannot be measured because of other forces, such as storm surge: “Storm surge could make the impacts of sea level rise worse in unpredictable ways.”

The researchers found that this statement eliminated the persuasive power of the scientists’ messages. When scientists acknowledged that storm surge makes the impact of sea level rise unpredictable, it decreased the number of participants who reported high trust in scientists by 4.9 percentage points compared with the participants who only read a most likely estimate of sea level rise.

The findings held true regardless of education levels and political party affiliation.

Not all expressions of uncertainty are equal, Howe said: “Scientists may want to carefully weigh which forms of uncertainty they discuss with the public. For example, scientists could highlight uncertainty that has predictable bounds without overwhelming the public with the discussion of factors involving uncertainty that can’t be quantified.”

Read the paper: Nature Climate Change

Article source: Stanford University

Author: Melissa De Witte

Image credit: Jody Davis / Pixabay

Nov 13
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Photosynthesis olympics: can the best wheat varieties be even better?

By Agriculture, News, Plant Science

Scientists have put elite wheat varieties through a sort of “Photosynthesis Olympics” to find which varieties have the best performing photosynthesis. This could ultimately help grain growers to get more yield for less inputs in the farm.

“In this study we surveyed diverse high-performing wheat varieties to see if their differences in photosynthetic performance were due to their genetic makeup or to the different environments where they were grown,” said lead researcher Dr Viridiana Silva-Perez from the ARC Centre of Excellence for Translational Photosynthesis (CoETP).

The scientists found that the best performing varieties were more than 30 percent better than the worst performing ones and up to 90 percent of the differences were due to their genes and not to the environment they grew in.

“We focused on traits related to photosynthesis and found that some traits behaved similarly in different environments. This is useful for breeders, because it is evidence of the huge potential that photosynthesis improvement could have on yield, a potential that hasn’t been exploited until now,” says Dr Silva-Perez.

During the study, published recently in the Journal of Experimental Botany, the scientists worked in Australia and Mexico, taking painstaking measurements in the field and inside glasshouses.

“The results that we obtained from our “Photosynthesis Olympics”, as we like to call them, are very exciting because we have demonstrated that there is scope to make plants more efficient, even for varieties working in the best conditions possible, such as with limited water and fertiliser restrictions. This means for example, that breeders have the potential to get more yield from a plant with the same amount of nitrogen applied,” says CoETP Director Professor Robert Furbank, one of the authors of this study.

Photosynthesis – the process by which plants convert sunlight, water and CO2 into organic matter – is a very complex process involving traits at different levels, from the molecular level, such as content of the main photosynthetic enzyme Rubisco, to the leaf, such as nitrogen content in the leaf and then to the whole canopy.

“This work is an important result for the CoETP, which aims to improve the process of photosynthesis to increase the production of major food crops such as wheat, rice and sorghum. There is a huge amount of collaboration, both institutional and interdisciplinary, that needs to take place to achieve this type of research. Without the invaluable cooperation between statisticians, plant breeders, molecular scientists and plant physiologists, we would have never achieved these results,” says co-author Tony Condon from CSIRO and the CoETP.

Read the paper: Journal of Experimental Botany

Article source: Arc Centre Of Excellence For Translational Photosynthesis

Author: Natalia Bateman

Image credit: Dr Viridiana Silva-Perez/COETP