A combination of behavior change campaigns and technology could help to keep air pollution at a minimum in schools

Creating campaigns that tap the diverse community around many of the UK's schools could help to keep air pollution low, especially as much of the country experiences the cost-of-living crisis, according to a new study from the University of Surrey.

Surrey's Global Centre for Clean Air Research (GCARE) found that campaigns aimed at changing the behaviour of parents, teachers and the local community, such as 'school street', can reduce outdoor nitrogen dioxide exposure by up to 23 per cent compared to business-as-usual activities. However, the study's authors believe behavioural change campaigns should be more inclusive and should consider the school's diverse communities and the local population.

Professor Prashant Kumar, the corresponding author of the study and founding- Director of the GCARE at the University of Surrey, said:

"Schools are going through lean times where every penny matters, and while some of the effective technologies in this study may appear unrealistic, the success of behavioural campaigns is clear from the evidence. Our study indicates that when local communities come together to raise awareness of air pollution, school exposure levels drop significantly.

"However, it is important that schools take into account the rich diversity of the school community, and their general local community. Health could be significantly improved and even lives saved through more air pollution awareness campaigns that target parents, schools and children, as well as business owners and the general public living around the school itself. Ideally this would be in addition to air-cleaning technologies -- and those responsible for school and healthcare funding should act on this. But even in isolation a real difference can be made through community-based behavioural changes."

GCARE researchers conducted a comprehensive literature review of how several technologies, such as HVAC (heating, ventilation and air conditioning) systems, air purifiers, and also behavioural changes can impact the concentration of pollution particles* in classrooms.

advertisement

---

The study also highlighted that installing ventilation and air conditioning systems with high-efficiency filters could reduce by up to 30 percent the concentration of fine particulate matter in classrooms compared with ambient concentration.

Their study also pointed out that air purifiers are effective in reducing the concentration of harmful particles by up to 57 per cent compared with no air purifier, and some were also able to reduce allergens, viruses and bacteria. Interestingly, indoor plants were shown to reduce volatile organic compounds by up to 73 per cent compared with no indoor plants in the classroom.

Professor Kumar, commented:

"If a school is fortunate enough to install many of these interventions, the big take away is that they should not be used in isolation. For example, air purifiers will not magically produce fresh air within a space. Therefore, a holistic approach to how these technologies and campaigns can work in a school context will be key to making sure that clean air is available to as many children as possible in the classroom."

This study has been published in the journal Science of Total Environment. This work builds upon GCARE's pioneering research around school guidance that has been released in over 20 countries and numerous co-designed studies with schools.

This work has been supported by the UKRI projects (EP/W001411/1; EP/T003189/1; EP/V052462/1) and network (EP EP/W034034/1; NE/V002341/1) projects.

Note  *Black Carbon, Ultrafine (PM0.1), fine (PM0.1-2.5) and coarse (PM2.5-10) particles

Story Source:

Materials provided by University of Surrey. Note: Content may be edited for style and length.

#Environment | https://sciencespies.com/environment/a-combination-of-behavior-change-campaigns-and-technology-could-help-to-keep-air-pollution-at-a-minimum-in-schools/

Forests benefit from tree species variety and genetic diversity

Reforestation projects should include a variety of tree species and ensure genetic diversity within each species to maximise new forests' health and productivity, suggests a study published today in eLife.

The findings suggest that complex interactions between trees and other organisms should be carefully considered when determining the combination of trees in a forest to ensure a functional ecosystem is maintained.

Diversity is essential to healthy ecosystems. Forests made up of a variety of tree species are more productive, as they make more efficient use of resources. This is because different species fill distinct niches -- meaning they have different optimal physical and environmental conditions, such as their terrain, and have different interactions with other species such as predation events, meaning they compete less. Additionally, having multiple tree species can reduce the negative impacts of herbivores and soil fungi that might compete for the trees' nutrients. Few studies have looked at the role of genetic diversity within each tree species in a forest, but some plant studies suggest that genetic diversity within a species is also beneficial to the ecosystem.

"To better understand the effects of genetic diversity in forests and guide reforestation efforts, we looked at how both the variety of species and genetic diversity within species affect forest productivity," says Ting Tang, the co-lead author of the study, a doctoral student at the University of the Chinese Academy of Sciences in Beijing, China.

Tang and colleagues used data from a long-term large tree species and genetic diversity experiment in a subtropical forest (www.bef-china.com, Bruelheide et al., 2014). Tree species diversity and genetic diversity within species were manipulated to generate four different plant diversity levels and the team measured five structural and chemical leaf traits that are known to be highly variable and relate to rates of resource acquisition.

The team's investigations showed that trees grown in forests with multiple tree species were more productive than those grown in single-species (or monoculture) forests. Forests with four different tree species had less diversity in soil fungi than monoculture forests, reducing the need for the trees to compete with fungi for resources. There was also less pressure from herbivores than in monoculture forests.

The team did not see reduced soil fungi diversity or herbivore pressure in forests that included one tree species with four distinct genetic backgrounds. But forests that had four different tree species -- with individual trees from four genetically distinct family groups in each -- did result in beneficial effects on both fungi diversity and herbivore pressure.

"We found that both species and genetic diversity promote forest productivity by increasing the ability of trees to maximise the use of resources while reducing damage caused by herbivores and competition from soil fungi," Tang comments.

The results suggest that species and genetic diversity could help reduce the number and variety of tree competitors -- for example, by reducing the toll that herbivores take on trees, the costs to trees of producing defensive compounds to deter them, or reducing the competition from fungi for nutrients. They also suggest trees in more diverse forests can better exploit individual niches.

"Reforestation projects are critical to mitigating atmospheric carbon levels and helping countries realise the full ecological and economic benefits of healthy forests," says Xiaojuan Liu, associate professor at the Institute of Botany, Chinese Academy of Sciences, Beijing. "Our results suggest that scientists leading reforestation projects should include multiple species of trees and genetically diverse individual trees within each species to ensure healthier forests."

Liu served as a co-senior author with Bernhard Schmid, a professor in the Department of Geography, University of Zurich, Switzerland, and Keping Ma, a professor at the Institute of Botany, Chinese Academy of Sciences.

Story Source:

Materials provided by eLife. Note: Content may be edited for style and length.

#Nature | https://sciencespies.com/nature/forests-benefit-from-tree-species-variety-and-genetic-diversity/

Dormant microbes can 'switch on' to cope with climate change

Dormant strains of bacteria that have previously adapted to cope with certain temperatures are switched back on during climatic change, according to a report published today in eLife.

The results have important implications for predicting the impact of global warming on ecosystems.

Microbes are integral to ecosystem function, because of their key roles as pathogens, food sources and in nutrient recycling. To understand the profound impact of climate change on the function of different ecosystems, it is therefore necessary to study the microbial communities within them.

"Microbial communities can respond to warming in the short term by acclimation -- developing unique traits to suit the environment -- or through the longer term by adaptation, where they make evolutionary changes over many generations," explains lead author Thomas Smith, Research Associate at the Georgina Mace Centre for the Living Planet, Imperial College London, UK. "But there is also a third mechanism, called species sorting, whereby the composition of the overall community -- that is, which species are present -- alters with changes in temperature. The importance of species sorting relative to acclimation and adaptation has not previously been explored in the context of microbial community responses to changing temperature. "

To address this, the team carried out a species sorting experiment, where they grew replicate soil bacteria communities collected from a single site at different temperatures ranging from 4°C to 50°C. They then measured the growth and metabolism of each isolated strain of bacteria across these different temperatures to determine their thermal performance, and studied the genetic sequences of isolated bacteria to see how temperature-response traits evolved over time.

They found that evolutionarily and functionally distinct communities emerged at each of the temperature conditions, driven by the resuscitation of microbial strains that had been inactive under previous environmental conditions. This suggests that -- rather than new bacteria moving into a community to suit the new conditions -- the parent community harbours multiple bacterial strains that are pre-adapted to survive at different temperatures and can switch on when their preferred temperature is reached. As a result, microbial communities in nature are likely to be able to respond rapidly to temperature fluctuations.

"Understanding the relative importance of acclimation, adaptation and species sorting in the assembly and turnover of microbial communities is key to determining how quickly they can respond to temperature changes. Until now, a mechanistic basis of these community-level responses had not been discerned ," concludes senior author Thomas Bell, Professor of Microbial Ecology at the Georgina Mace Centre for the Living Planet, Imperial College London. "We have found that the resuscitation of functional diversity within a microbial community can allow the whole community to survive in response to temperature changes. Further studies on other microbial communities -- such as those residing in water -- will support more accurate predictions of the effects of climate change on different ecosystems."

Story Source:

Materials provided by eLife. Note: Content may be edited for style and length.

#Nature | https://sciencespies.com/nature/dormant-microbes-can-switch-on-to-cope-with-climate-change/

Husker study: Brazil can grow more soybeans without deforesting Amazon

Developing countries around the globe face a challenge that pits economic growth against environmental protection. As they expand their agricultural production, they often convert forest into cropland and pasture. But the large-scale removal of trees weakens the world's ability to prevent further climate deterioration and biodiversity loss.

Brazil presents a key example. The country is home to the world's largest area of rainforest -- some 1.2 million square miles, an area more than 16 times the size of Nebraska. The Amazon contains large tracts of rainforests that, when converted to agriculture, release a huge amount of carbon dioxide into the atmosphere, exacerbating climate change.

Increasing agricultural production is a national priority for Brazil, the world's largest soybean exporter. Since the 1990s, agricultural encroachment has eroded major areas of the country's rainforest. During 2015-19, the Amazon basin accounted for a third of the land converted for Brazilian soybean expansion.

A newly released four-year study by the University of Nebraska-Lincoln and its research partners in Brazil identifies a path forward that would allow Brazil to strengthen its agricultural sector while safeguarding the rainforest. The scientists' recommendations have broad applicability to other developing countries facing a similar challenge.

"In the current context of high grain prices and food supply disruptions, we believe there is a critical need for major crop-producing countries to reassess their potential to produce more on existing cropland," the authors wrote in an article published Oct. 10 in the journal Nature Sustainability. "Without an emphasis on intensifying crop production within the existing agricultural area, coupled with strong institutions and policies that prevent deforestation in frontier agricultural areas, it would be difficult to protect the last bastions of forests and biodiversity on the planet while being sensitive to the economic aspirations of countries to develop."

Since 2000, moratoria and incentives have been used to slow deforestation in Brazil. However, sharply increased commodity prices and political pressure to quickly recover from combined impacts of the COVID-19 pandemic and war in Ukraine have placed the Amazonian rainforest under heightened threat. If current trends continue, Brazil will convert about 57 million acres to soybean production in the next 15 years, with about one-fourth of the expansion occurring in environmentally fragile lands such as rainforest and savannah.

advertisement

---

Yet prohibiting cropland expansion would cost Brazil an estimated $447 billion in lost economic opportunity through 2035.

The study led by Patricio Grassini, Sunkist Distinguished Professor in Agronomy and associate professor in the Department of Agronomy and Horticulture at Nebraska, shows how it could be possible for Brazil to expand its agricultural production without converting more rainforest and savannah to crops. With a carefully managed strategy to intensify production on existing acres, the country could increase its annual soybean output by 36% by 2035 while reducing greenhouse gas emissions by 58% compared to current trends.

Grassini and his co-authors describe a three-pronged "intensification" strategy that calls for:

* Significantly increasing soybean crop yields. * Growing a second crop of corn on soybean fields in certain areas. * Raising more cattle on smaller pastures to free up more land for soybeans.

Brazil's tropical and subtropical climates make it possible to cultivate two crops on the same land during the growing season in most regions, Grassini said. Plus, "livestock production is huge in Brazil," he said, "and our study shows there is a big opportunity for Brazil to increase livestock-based production systems and by doing so, free up some of the area currently used for livestock production and use that land for producing more soy."

Detailed modeling for the project indicates that by 2035, the strategy could boost Brazil's soybean production by 36%. At the same time, Grassini said, Brazil could "eliminate deforestation completely and essentially reduce the amount of carbon dioxide equivalents released into the atmosphere, helping to mitigate climate change."

advertisement

---

"This approach strengthens agriculture while protecting fragile ecosystems that are important from a perspective of climate change mitigation as well as biodiversity conservation," he said.

To determine how much yields could be improved on existing Brazilian farm ground, the scientists examined soybean production in four key regions: the Pampa and the Atlantic Forest regions along the Atlantic coast, where soybean cultivation has been underway for about 50 years, and the Amazon and the Cerrado regions in Brazil's interior, where soybean production began after the turn of the 21st century. The analysis made extensive use of the Global Yield Gap Atlas previously developed by Grassini and colleagues at Nebraska. The atlas is the world's leading database on high-quality agronomic data, covering more than 15 major food crops across more than 75 countries.

"By showing that it is possible to produce more on existing agricultural land," the scientists wrote, "this research study is bringing real solutions to the table and can have a massive impact to help Brazil produce more while protecting the environment."

Success on the dual goal of agricultural expansion and protecting the forest will require strong institutions, proper policy and enforcement to make sure those productivity gains effectively translate into forest preservation, Grassini cautioned. Still, the intensification approach can help achieve a reasonable balance between crop production and the protection of fragile ecosystems.

Grassini's team calculated three scenarios in the four key regions: "business as usual," where existing trends would continue; "no cropland expansion," where additional land conversion would be prohibited; and "intensification," where steps would be taken to increase yields, encourage second cropping and concentrate cattle production. They concluded the intensification strategy would enable Brazil to realize 85% of the projected gross income from soybean and second-crop maize, compared to current trends, while reducing global climate warming by 58%.

The four-year project involved collaboration between the University of Nebraska-Lincoln and universities in Brazil, including the University of Sao Paulo, Federal University of Santa Maria and University of Goias, as well as Embrapa, the leading agricultural research organization in Brazil. Coauthors on the project included Juan Pablo Monzon and José F. Andrade, former research assistant professors in agronomy and horticulture at Nebraska. The project was funded by the International Plant Nutrition Institute, Research Foundation of the State of São Paulo, Brazilian Research Council, Research Foundation of the State of Rio Grande do Sul, and the Global Engagement Office in Nebraska's Institute of Agriculture and Natural Resources through the FAPESP-UNL SPRINT program.

Fabio R. Marin, a Brazilian scientist who was the main author of the paper along with Brazilian scientist Alencar J. Zanon, received financial support from the Fulbright program to support a six-month stay at Nebraska.

#Nature | https://sciencespies.com/nature/husker-study-brazil-can-grow-more-soybeans-without-deforesting-amazon/

Biodiversity in Africa and Latin America at risk from oil palm expansion, new report warns

Zero deforestation commitments may inadvertently leave vital habitats in Latin America and Africa vulnerable to agricultural expansion, a new study has found.

The study highlights how sustainability commitments, which play an important role in preventing the destruction of tropical rainforest, fail to protect nature in tropical grassy and dry forest habitats such as the Llanos in Colombia, Beni savanna in northern Bolivia, and Guinean and Congolian savannas in West and Central Africa.

The research team, led by the University of York, calculated that if oil palm producers cleared these habitats to make way for new plantations, a third of vertebrates on the International Union for Conservation of Nature's red list of threatened species could be affected, including the blue-throated macaw in Bolivia, the giant pangolin in Congo, and the Hellmich's Rocket Frog in Colombia.

For the study, researchers mapped the areas around the globe that are at risk from new oil palm plantations. They identified 167 million hectares that are potentially suitable for the crop while still meeting the Roundtable on Sustainable Palm Oil's (RSPO) definition of 'zero deforestation'. Of those 167 million hectares, 95 million are in grasslands and dry forests, mostly in South America and Africa.

As global demand for agricultural land increases researchers are calling for urgent protections for these habitats, which support a rich array of species and act as an important carbon store.

Co-author of the study, Professor Jane Hill from the Department of Biology and the Leverhulme Centre for Anthropocene Biodiversity at the University of York, said: "Palm oil is at the sharp edge of debate on how we can balance the need to feed the world and sustain livelihoods, while protecting nature.

advertisement

---

"With a yield estimated to be six times higher than many other vegetable oils such as oil seed rape, palm oil is regarded as a miracle crop and it supports the livelihoods of millions of people in tropical countries around the world. So rather than avoiding or banning palm oil, we need to ensure effective international policies and governance to protect, not just tropical rainforest, but tropical grasslands and dry forests too.

"Our study highlights how current sustainability commitments could have the unintended consequence of putting areas of remarkable biodiversity at risk from the expansion of oil palm agriculture."

Since 2018, many oil palm companies have signed up to the RSPO's zero deforestation commitments, which means they cannot expand plantations into tropical rainforest or peatlands.

While concern from buyers and consumers about the environmental impact of palm oil has helped to drive membership of the scheme, many oil palm producers are yet to sign up to these commitments.

First author, Dr Susannah Fleiss, who carried out the study while researching her PhD at the University of York, said: "Although we found that oil palm yield in areas currently covered by grassland and dry forest would be lower than in tropical rainforest, these sites would still be attractive for the expansion of oil palm agriculture. We also found that irrigation would improve yield in many of these locations, potentially making them more attractive for expansion.

advertisement

---

"Clearing these areas for plantations would have a serious impact on biodiversity, potentially reducing the ranges of one quarter of vertebrate species that are currently threatened with extinction. Plantation development would replace the existing habitat in these areas, disrupting the ability of the species present to find food and water, and affecting their migration routes.

"Large numbers of people live in tropical grassy and dry forest regions, where they often play a critical role in ecological processes such as burning and grazing. The expansion of oil palm agriculture in these areas could lead to a number of interlinked issues for local people and biodiversity.

"Our study highlights the strong need for internationally-coordinated governance to protect these habitats, in addition to the existing global efforts to protect tropical rainforest."

Co-author Dr Phil Platts, Honorary Fellow at the University of York and Director of Earth Observation at BeZero Carbon, said: "Sustainability guidelines for palm oil were developed in the context of Southeast Asia's rainforests, and so reflect the structure and function of those habitats. Now expansion is shifting to different ecological contexts, the scope of sustainability commitments must similarly expand, in line with the distinct biodiversity and carbon stocks now under threat."

The research, published in the journal Nature Ecology and Evolution, is funded by Unilever, in collaboration with the University of Liverpool, Oxford, the Potsdam Institute for Climate Impact Research, Unilever and BeZero Carbon.

#Nature | https://sciencespies.com/nature/biodiversity-in-africa-and-latin-america-at-risk-from-oil-palm-expansion-new-report-warns/

How extinct Steller's sea cow shaped kelp forests

For millions of years, the Steller's sea cow, a four-ton marine mammal and relative of the manatee, shaped kelp forests along the Pacific coast of North America by eating massive quantities of kelp fronds from the upper canopies, thus allowing light to spur productivity in the understory. In a paper published today in Frontiers in Ecology and Evolution, researchers from the California Academy of Sciences -- as part of the Academy's Thriving Californiainitiative -- reveal what historical kelp forests may have looked like in the presence of the marine megaherbivore, which went extinct in the 1700s just 27 years after its first encounter with Europeans due to overhunting, and suggest how kelp forest conservation efforts can take its absence into account.

"Kelp forests are highly productive ecosystems. They act as storm buffers, are economically important for fishing, and are home to countless marine organisms, yet they are in steep decline throughout the Pacific," says study author and Academy Curator of Geology and Invertebrate Zoology Peter Roopnarine, PhD. "When kelp forests were evolving millions of years ago, there were large marine herbivores like the Steller's sea cow, which are now extinct. So when it comes to what's driving their widespread decline, there might be a major component we're missing."

This tendency to evaluate the state of modern ecosystems based on their recent past is known as shifting baseline syndrome and can obscure how an ecosystem may have existed over much longer periods of time.

"We already see the consequences of this thinking with things like wildfire management," Roopnarine says. "In the short-term, wildfires have been seen as something to suppress because of the damage they bring to forest ecosystems. But recently we have learned that, in the long run, wildfires are a natural part of those systems that can lead to healthier, more resilient forests."

A new approach to address shifting baselines

In the paper, the researchers propose -- and advocate for -- a new way of evaluating the overall health of ecosystems to avoid the pitfalls of shifting baseline syndrome, called the Past-Present-Future (PPF) approach.

advertisement

---

As opposed to evaluating an ecosystem based on its current state, the researchers say the PPF approach, which combines historical lines of evidence from museum specimens and the fossil record with Indigenous traditional ecological knowledge and modern scientific data, can lead to mathematical models that more accurately depict natural systems. Importantly, these models can then be operationalized for more effective conservation.

"Today, we are surrounded by severely degraded ecosystems, places that were far healthier a mere century ago, let alone a millennium or more," says study author and Academy Executive Director Scott Sampson, PhD. "Growing numbers of these ecosystems are now in danger of collapse, even if we protect them. So if we are to help guide a given place toward a flourishing future, we must understand not only its current state of health, but past states as well, and then apply these insights toward calculated, regenerative interventions. This Past-Present-Future approach to conservation has the potential to be revolutionary."

Uncovering the "sea cow effect"

To get a better picture of kelp forests of the past -- and therefore a better baseline from which to compare against the state they are in today and predict how they might change in the future -- the researchers built a mathematical model using historical and modern data to simulate how the ecosystem might respond under different scenarios.

First, the researchers input the effects different players in the ecosystem have on kelp forests, such as predation of kelp by sea urchins or predation of urchins by sea otters. The model was then compared against pre-existing data on kelp forests to ensure it reproduced how the ecosystems function in real life.

advertisement

---

Once the researchers refined the model, they were then able to explore how the Steller's sea cow impacts kelp forests by adding them to the model and seeing how the ecosystem responded over time.

"One of the more important and surprising findings was that including the Steller's sea cow resulted in a totally different type of kelp forest," says study author and postdoctoral researcher at the Academy and the University of Nevada Las Vegas Roxanne Banker, PhD. "Instead of kelp-dominated, which is what we think of with modern forests, the sea cow's presence and predation of the upper canopy would have resulted in more of a balance between kelp and algae as more sunlight would have reached the sea floor."

Banker adds that this finding is of particular significance when reflecting on the current state of kelp forests, which are heavily degraded due in part to overpredation from sea urchins. "Algae would provide an additional food source for urchins, potentially reducing their impact on kelp," she says.

The study also showed that when the sea cow was present, the kelp forests as a whole were often more resilient: Even under adverse conditions, such as ocean warming or disease outbreaks, kelp forests may have been less likely to transition to the barren urchin-dominated state that is often seen today, and when they did they more quickly recovered to a forested state. This effect, which the researchers dubbed the "sea cow effect," provides actionable insights for current kelp conservation efforts.

"If our model was further validated through experimentation on test plots, it could allow us to build more resilience into kelp forests by modeling the efficacy of different interventions," Roopnarine says. "Selectively harvesting the upper fronds of the kelp canopy, for instance, to recreate the role that was lost with the Steller's sea cow."

#Environment | https://sciencespies.com/environment/how-extinct-stellers-sea-cow-shaped-kelp-forests/

Researchers discover root exudates have surprising and counterintuitive impact on soil carbon storage

Ecosystem ecology studies often focus on what's happening to plants above ground, for instance exploring photosynthesis or water loss in leaves. But what is happening below the ground in plant roots is equally important when evaluating ecosystem processes.

In a new study in Nature Geoscience researchers in the Department of Organismic and Evolutionary Biology at Harvard University examined root exudates and their impact on soil carbon storage revealing surprising and counterintuitive results.

Root exudates are organic carbon compounds (such as simple sugars, organic acids, and amino acids) released from living plant roots into the soil. These small molecules can bind directly to soil minerals, making them important regulators of soil carbon formation and loss. Unlike plant litter (such as leaves and roots), which must be decomposed before it can affect the soil carbon pool, root exudates can have immediate effects on mineral-associated organic matter (MAOM), which contains long-cycling, "stable" soil carbon.

Several studies show that anthropogenically elevated atmospheric CO₂ concentrations are likely to increase the rate of plant root exudation and change the chemical composition of root exudates. Lead author Nikhil R. Chari, Ph.D. candidate, and senior author Professor Benton N. Taylor tested how these changes may affect soil carbon by examining how changing the rate of root exudation and the composition of exudates affected native soil-carbon dynamics in a temperate forest.

Chari and Taylor collected soil cores from Harvard Forest, a temperate hardwood forest in central Massachusetts, and incubated them directly in centrifuge tubes. They then fabricated three different carbon-13 root exudate "cocktails" of simple sugar, organic acid, and amino acid. They delivered the "cocktails" to the soil cores via "artificial roots" at two different rates over a thirty-day period. Unlike other studies, Chari and Taylor did not use homogenized or artificial soils. Their sampling method preserved large amounts of heterogeneity in soil carbon and microbial communities present in the forest.

"We wanted to know if these mechanisms were having an effect at ecologically meaningful scales," said Chari. "We used intact soil cores to test if the effect of root exudates would overcome the natural heterogeneity in the system."

The researchers measured both initial and final carbon stocks in the cores. They found that contributions of root exudates to soil carbon were driven by contributions to the long-cycling MAOM fraction. MAOM are microscopic coatings on soil particles made mostly of the byproducts of bacteria and fungi. MAOM stays in the soil for decades meaning it can maintain carbon in soil for a very long time.

advertisement

---

At higher rates of root exudation the MAOM carbon pool did not change even as root exudate contributions to MAOM increased. But at lower rates of root exudation Chari and Taylor observed net MAOM carbon accumulation, even though the exudate contributions were not as great.

"You would think that if you increase the rate of root exudation you would increase carbon input into the soil forming more soil carbon," said Chari, "but we found instead an opposite effect that offset the increase in carbon."

The researchers refer to this as the priming effect. Priming occurs when the input of new soil carbon prompts the decomposition of old soil carbon. Enhanced rates of root exudation appeared to increase rates of MAOM priming relative to rates of MAOM formation.

"First principles would suggest that the more carbon we push into the soil via exudation, the more carbon is going to accumulate in these MAOM fractions. When, in fact, that doesn't seem to be the case," said Taylor. "In reality, you get more MAOM formation, but you also get more loss of it and it balances out. You don't actually get more carbon sticking around in the soil, even when you're pushing more in."

Chari and Taylor also found the different exudate compounds each had different effects on the soil carbon. Glucose (simple sugar) produced higher MAOM turnover both in formation and loss, but there was no net accumulation of MAOM. While succinic acid (organic acid) and aspartic acid (amino acid) drove lower rates of MAOM formation, but did result in a net MAOM carbon accumulation. Interestingly, the researchers found that amino acids had a particularly strong positive effect in increasing microbial biomass carbon formation, while organic acids did not. These findings again suggests the larger microbial community enhances the microbial priming effect. The results further validate that predicted increases in root exudation rates and a shift toward simple sugars caused by global change may reduce soil's carbon storage capacity.

"These changes are happening ubiquitously below the soil surface, yet even tiny changes in this process can have huge implication for soil carbon storage," said Taylor. "People know that processes in a leaf are important, but every root below our feet has a huge impact on carbon in the soil. And elevated CO₂, warming, or other climate change drivers, could cause soil carbon loss to increase disproportionately to soil carbon formation."

Going forward, Chari and Taylor continue to measure changes in the rate and composition of root exudates under elevated CO₂ and warming in a variety of different ecosystems, including temperate forests, grasslands, and corn and soybean agricultural fields.

#Nature | https://sciencespies.com/nature/researchers-discover-root-exudates-have-surprising-and-counterintuitive-impact-on-soil-carbon-storage/