The findings, published in the journal Biogeochemistry, challenge a lingering assumption in soil science: that management can meaningfully influence the fast-cycling carbon in soil but has little effect on the slow, stable pool. If that assumption had held, the climate benefits of improved farming would have been modest. Instead, the Vermont data suggest that when farmers build soil health, they build durable carbon too.

Soil is the largest active terrestrial carbon reservoir, holding roughly 70 to 80 percent of the carbon stored on land. How much of that carbon stays put depends largely on which of two physical pools it occupies. Particulate organic carbon (POC) consists of partially decomposed plant fragments larger than 53 micrometers—recognizable bits of root and leaf litter that microbes can consume relatively easily. Mineral-associated organic carbon (MAOC), by contrast, is smaller than 53 micrometers and consists of organic compounds chemically bound to clay and silt particles, including the remains of microbes themselves. Because microbes cannot easily reach carbon locked onto mineral surfaces, MAOC persists far longer in soil, making it the prize for any climate mitigation strategy that depends on keeping carbon out of the atmosphere.

To disentangle what controls each pool, the team collected soil samples following the Comprehensive Assessment of Soil Health protocol: ten subsamples of the top 15 centimeters taken in a zigzag pattern across each field, composited and split between Cornell University’s Soil Health Lab and Dartmouth’s Hicks Pries Lab. Fields represented silage corn, hay, pasture, wheat, and mixed vegetable operations, spanning Vermont’s range of soil textures, climates, and management styles. Clay content across sites ranged from about 6 to 54 percent, soil carbon concentrations from 1.45 to 8.68 percent, and mean annual temperature from 4.56 to 8.56 degrees Celsius.

In the laboratory, the researchers performed size fractionation. After drying samples at 90 degrees Celsius and dispersing aggregates with a 0.5 percent sodium hexametaphosphate solution shaken for 24 hours, they wet-sieved the soil through a 53-micrometer mesh. Material retained on the sieve constituted POC; material passing through was MAOC. Each fraction was then dried, ground, and weighed into tin capsules for carbon and nitrogen analysis on an elemental analyzer. Where high pH hinted at carbonate contamination, the team verified inorganic carbon with a hydrochloric acid fizz test and removed it, finding negligible effects on the results.

The numbers told a clear story about management. Hay and pasture fields contained, on average, 69 percent more POC and 30 percent more MAOC than corn silage and vegetable fields. Carbon stocks to 30 centimeters were 17 percent greater in hay fields than in corn fields and 32 percent greater than in vegetable fields. The management history the team could obtain helped explain why: among fields with reported tillage data, 95 percent of pastures and 59 percent of hay fields were in no-till, versus just 7.5 percent of corn fields and 4.5 percent of vegetable fields. Perennial fields also boasted 83 percent greater aggregate stability—resistance of soil clumps to breakdown—which the statistical models identified as a strong positive predictor of both carbon fractions.

Aggregate stability matters mechanistically. Stable macroaggregates, larger than 250 micrometers, physically shelter organic matter from decomposers. Perennial grasses and legumes in hay and pasture contribute abundant root biomass and exudates; belowground inputs from roots outnumber aboveground inputs by roughly eight to one in agricultural systems, and roots feed the microbial activity that both breaks down POC and generates the microbial necromass that ultimately becomes MAOC. Manure inputs, common on livestock farms, likely accelerate this conversion by fueling decomposers.

Climate and texture left their fingerprints as well, in ways that depended on one another. POC concentrations rose with precipitation at cooler sites but flattened at warmer ones, consistent with moisture and temperature jointly governing the balance between plant input and microbial decomposition. More strikingly, MAOC responded to a three-way interaction among clay content, mean annual temperature, and mean annual precipitation. In clay-rich soils, MAOC increased with warming, especially where rainfall was abundant—warmer, wetter conditions boost plant productivity and microbial processing, delivering more dissolved organic carbon onto abundant mineral surfaces. In low-clay soils the pattern reversed or vanished: with fewer sorptive surfaces available, intensified decomposition under warm, wet conditions led to carbon loss through leaching and mineralization rather than stabilization.

Crucially for the carbon sequestration debate, the team found that Vermont’s farm soils remain well below their mineral saturation point. Comparing MAOC concentrations against the relationship between clay-plus-silt content and MAOC established by a recent global analysis, the measured values fell far beneath the saturation threshold. That means these soils retain genuine capacity to lock away more persistent carbon—capacity that management can exploit. Perennial crops, the data suggest, are among the most effective ways to do so, simultaneously maximizing both POC and MAOC.

Perhaps the most consequential result is the link to soil health scoring. The Cornell framework assigns each field a composite score integrating biological, chemical, and physical metrics such as active carbon, aggregate stability, pH, and organic matter content. The researchers found that every one-unit increase in the soil health score corresponded to a 3.15 percent increase in POC concentration and a 2.25 percent increase in MAOC concentration. Carbon stocks to 30 centimeters rose by roughly 0.25 kilograms of carbon per square meter per score unit, and the relationship was tight, explaining 60 percent of the variance in stocks. A commonly used quick indicator, permanganate-oxidizable “active” carbon, also correlated positively with both fractions, though it proved the least sensitive of the carbon measures to differences among crop types.

One nuance deserves attention: while absolute MAOC rose with soil health scores, the proportion of total carbon in mineral-associated form declined slightly, because POC accumulated even faster. Corn fields actually showed a higher MAOC proportion than pastures—not because they held more stable carbon, but because tillage and low residue inputs had stripped away the vulnerable POC, leaving the remainder proportionally enriched. A high MAOC proportion, in other words, can signal degradation rather than health.

The study’s observational design means management and environment cannot be fully separated—farmers choose crops partly based on the land they have. But the authors note that the one consistently significant difference among crop types, aggregate stability, is a soil property highly responsive to management. Soil pH, often suspected of controlling carbon dynamics, played no significant role here, likely because lime applications kept fields within a narrow and favorable range.

The implications reach beyond Vermont’s dairy belt. Meta-analyses across Europe and the Americas have found cover cropping increases POC by about 15 percent and MAOC by 5.6 percent, and studies in semi-arid systems show similar responsiveness to perennial vegetation. If farmers, agricultural extension programs, and carbon-credit markets can use routine soil health tests as a proxy for durable carbon gains, the pathway to financing regenerative practices becomes considerably simpler. As the authors conclude, building soil health and building long-term soil carbon are, it turns out, far more aligned than they are in conflict.

The field warming experiment, situated at the Rocky Mountain Biological Laboratory in Colorado, utilized experimental heaters to simulate increased temperatures year-round over an extensive 29-year period. This prolonged warming led to a marked ecological transition known as “shrubification,” where the once-thriving grassy meadows, dominated by species such as fescue and sunflowers, gradually gave way to shrub-dominated landscapes primarily characterized by sagebrush. The gradual replacement of herbaceous plants by shrubs constitutes a fundamental shift in ecosystem structure and function, altering both the spatial and temporal availability of resources like light, water, and nutrients.

What distinguishes this research is the thorough exploration of subterranean community responses alongside aboveground vegetation changes. Research teams led by Souza and her colleagues Stephanie Kivlin, Aimée Classen, and Jennifer Rudgers extended their analysis beyond surface soil layers to investigate microbial and fungal populations at greater depths in 2019. This deep soil sampling revealed that the warming-driven shift in plant communities corresponded with significant restructuring of root-associated fungal assemblages, indicating a decoupling of historical plant-fungal symbiotic relationships. The data demonstrated a pronounced decline in mycorrhizal fungi, which traditionally form mutualistic partnerships with plants to facilitate water and nutrient uptake in exchange for carbon, while saprotrophic fungi, responsible for breaking down organic matter, showed increased prevalence in warmed soils.

This observed decline in mycorrhizal fungi under sustained warming challenges previous assumptions that symbiotic fungi might adapt or acclimate to heightened temperatures over time. Instead, the disruption of these crucial mutualisms signals a transformative change in belowground ecological interactions, with profound implications for nutrient cycling and carbon sequestration. The diminished presence of mycorrhizal fungi suggests that plants in these warming meadows may face increased stress in acquiring essential nutrients, potentially altering plant growth strategies and ecosystem productivity.

The shift from fast nutrient cycling in herbaceous meadows to slower, conservative nutrient turnover in shrub-dominated environments illustrates a fundamental change in ecosystem functioning. Originally, grassland ecosystems promoted rapid nutrient uptake and recycling, maintaining high productivity and nutrient availability. Conversely, shrubified ecosystems exhibit more conservative resource use, reducing nutrient turnover rates and potentially increasing soil dryness and aridity. This shift can cascade through trophic levels, impacting herbivores and other wildlife dependent on the quality and quantity of forage available in these habitats.

Moreover, this research exemplifies the “coupling” and “decoupling” of aboveground and belowground processes in response to climate perturbations. While plant communities exhibited clear changes in species composition and structure, their associated fungal symbionts responded differentially. The observed decoupling signifies that aboveground vegetation shifts may no longer predict belowground microbial dynamics, complicating efforts to model and forecast ecosystem responses to global change. Understanding these differential responses is critical, as symbiotic fungi play a vital role in ecosystem resilience, soil carbon storage, and nutrient cycling.

The experimental warming setup at the Rocky Mountain Biological Laboratory serves as a model system for predicting the long-term impacts of climate change on montane ecosystems globally. The persistent increase in temperature imposed by the heaters simulates realistic warming scenarios projected under anthropogenic climate trajectories. Thus, the insights gleaned from this system provide a window into potential future ecological configurations, demonstrating how sustained warming can drive transitions not only in plant community composition but also in fundamental ecosystem processes mediated by fungi and microbes.

Furthermore, the findings illuminate the fragility of mutualistic interactions under climate stress. The collapse or reduction of mycorrhizal networks may impair the ability of plants to cope with environmental changes, potentially leading to decreased productivity, altered species distributions, and diminished ecosystem services. Such ecosystem service losses—ranging from nutrient cycling efficiency to wildlife foraging habitat—highlight the broader consequences of microbial community shifts extending beyond immediate soil processes.

The collaboration among institutions—University of Oklahoma, University of Tennessee, University of Michigan, and University of New Mexico—exemplifies the interdisciplinary approach necessary to tackle complex ecological questions. By integrating plant ecology, soil microbiology, fungal biology, and climate science, the team constructed a holistic understanding of ecosystem transformations under warming conditions, bridging gaps between above and belowground biological domains.

Despite these advances, researchers emphasize the necessity for ongoing investigation to delineate the temporal dynamics and potential reversibility of these changes. Questions remain about how long it takes for complete decoupling of plant and fungal communities to occur, whether mitigation efforts could restore historic symbiotic balances, and how these belowground shifts interact with other global change factors, such as altered precipitation patterns or land use changes.

This comprehensive study acts as a bellwether for the complex feedbacks between climate change and ecosystem biology. It signals that warming-induced plant community shifts are accompanied by profound subterranean microbial reorganizations that alter nutrient dynamics and ecosystem resilience. As climate warming accelerates worldwide, the fate of such montane ecosystems may depend heavily on these microbially mediated feedbacks, which in turn influence carbon storage potential and biodiversity conservation outcomes.

In summary, this groundbreaking research reveals that experimental warming not only triggers “shrubification” in mountain meadows but also causes a critical decoupling of plant–fungal symbioses. This decoupling results in a transition toward ecosystems with slower nutrient recycling and reduced microbial diversity, which could dramatically reshape ecosystem services. These findings underscore the urgency of considering soil microbial dynamics within climate change models to better forecast ecosystem trajectories and develop adaptive management strategies.

Subject of Research: Climate change impacts on plant-fungal symbiotic interactions and ecosystem functioning in high-elevation mountain meadows.

Article Title: Experimental warming decouples plant-fungal symbiont interactions and leads to a more conservative ecosystem.

References: Proceedings of the National Academy of Sciences

Image Credits: University of Oklahoma

Keywords: Climate change effects, Mycorrhizal fungi, Fungi, Shrubs, Symbiosis, Mutualism

Nitrous oxide emissions predominantly originate from denitrification, a microbial process in soils where excess fertilizers are converted into nitrogen gases. This transformation, essential to the nitrogen cycle, comes with the unintended consequence of releasing N2O into the atmosphere. Historically, efforts to curtail these emissions have centered on managing fertilizer application and manipulating microbial populations. However, limited attention has been given to the soil virome—the vast community of viruses inhabiting the earth beneath our feet—and its ecological impacts.

Researchers affiliated with the Chinese Academy of Sciences embarked on meticulously controlled laboratory experiments to elucidate the influence of viral particles on soil nitrogen dynamics. Utilizing farm soil from the North China Plain, a hotspot for fertilizer usage and associated nitrogen losses, they introduced varying concentrations of active virus extracts. These experimental setups were rigorously monitored using a combination of gas flux measurements and high-throughput genetic sequencing techniques, providing robust evidence that soil viruses could decrease N2O emissions by as much as 20% relative to untreated controls.

Delving deeper into the mechanisms, the study reveals that viruses do not indiscriminately affect soil microbial communities. Instead, they specifically target denitrifying bacteria possessing the genetic machinery to produce nitrous oxide. Prominent among these microbial groups are members of the Pseudomonadota phylum, ubiquitous soil bacteria recognized for their role in nitrogen cycling. Viral predation on these groups results in diminished N2O generation, underscoring a fine-tuned ecological interaction with profound implications for greenhouse gas regulation.

Further network analyses illuminated the complexity of virus-microbe interactions under increased viral loads. Soils enriched with viruses exhibited a dense network of interactions, indicative of the viruses reshaping microbial community structure dynamically. These findings attest to viruses as active ecological engineers rather than passive soil inhabitants, capable of modulating microbial functions that underpin biogeochemical cycles and atmospheric chemistry.

Senior author Shuping Qin emphasized the paradigm shift this research entails: viruses are not solely agents of destruction but may be harnessed as allies within climate-smart agricultural strategies. This newly uncovered role for viruses paves the way for innovative approaches that leverage phage therapy concepts—where viruses are deliberately employed to modulate microbial populations—to specifically suppress microbes responsible for greenhouse gas emissions.

Despite the encouraging laboratory results, the translation of these findings to open-field agricultural systems remains a critical next step. The research team calls for extensive studies addressing the stability, efficacy, and safety of viral applications under variable environmental conditions. Real-world soils present complex challenges, from microbial diversity shifts to potential off-target effects, which must be navigated to unlock viral solutions for sustainable nitrogen management.

Beyond their immediate climate benefits, the involvement of viruses in soil nitrogen cycling invites a reevaluation of soil ecosystems’ intricacy. Viruses represent an often-overlooked dimension of soil biodiversity that can influence nutrient turnover and ecosystem resilience. Recognizing their role enriches our understanding of terrestrial microbial ecology and opens novel research avenues at the interface of virology, microbiology, and environmental science.

The strategic use of soil viruses to mitigate nitrous oxide emissions aligns well with global efforts to reduce agriculture’s environmental footprint. Fertilizer-driven nitrogen losses contribute not only to greenhouse gas accumulation but also to water eutrophication and ecosystem disruption. Targeting denitrifiers through viral means may offer a dual advantage by lowering atmospheric N2O release and enhancing nitrogen retention in soils, thereby improving fertilizer use efficiency.

Methodologically, the study set a precedent by combining classical soil gas measurement techniques with cutting-edge molecular tools. The integration of metagenomics enabled precise identification of viral targets and elucidation of shifts in bacterial community composition post viral infection. Such interdisciplinary approaches are critical for untangling the complex soil microbiome interactions and charting pathways for intervention.

This research underscores the need for a holistic approach to climate mitigation, embracing both the micro and macro facets of ecosystem functioning. The hidden potential of viruses as natural regulators within the nitrogen cycle exemplifies the remarkable interdependencies shaping our planet’s biogeochemical health. Harnessing these relationships could revolutionize agricultural management and contribute significantly to meeting global climate targets.

In summary, the discovery that soil viruses can selectively infect denitrifying bacteria to curb nitrous oxide emissions invites a transformative perspective on microbial ecology and climate change mitigation. It challenges conventional narratives about viruses and spotlights them as crucial, yet underappreciated, players in sustaining environmental balance. As investigations continue, the prospect of virus-informed agriculture offers a promising frontier in our collective quest for a sustainable future.

Subject of Research: Not applicable

Article Title: Viruses mitigate soil nitrogen loss and N2O emissions during denitrification by selectively infecting denitrifiers

News Publication Date: 17-Sep-2025

References:
Song W, Yao J, Fu Y, Qin S. 2025. Viruses mitigate soil nitrogen loss and N2O emissions during denitrification by selectively infecting denitrifiers. Nitrogen Cycling 1: e004. DOI: 10.48130/nc-0025-0002

Image Credits: Wei Song, Jinzhi Yao, Yingdong Fu & Shuping Qin

Keywords: Nitrogen cycle, Nitrogen, Climate change, Greenhouse gases