The study area lies in the municipality of Rianxo, where the temperate-oceanic climate delivered an average temperature of 15.7 degrees Celsius and an accumulated precipitation of 1,774 liters per square meter in 2024. The parent material is mainly granitic, and the soils are mostly classified as Leptosols and Umbrisols. These forests are communal properties, owned collectively by villagers, and the sampling was carried out in collaboration with forest owner associations across five forest communities, from Campelo Vilar e Cerqueiras to Leiro, at altitudes ranging from 50 to 485 meters above sea level. In each of the 54 stands, the team collected 10 subsamples along a zig-zag transect, compositing them into a single sample per plot from the 0 to 20 centimeter soil layer in the summer of 2024.

Galician forest soils are, in general, acidic, rich in organic matter and poor in phosphorus. The measurements confirmed this regional signature: pH values ranged between 4.63 and 5.6, soil organic matter between 12.1 and 20.9 percent, nitrogen between 0.41 and 0.69 percent, and extractable phosphorus between just 4.0 and 8.4 milligrams per kilogram. The researchers attribute these properties primarily to the humid climate, which drives intense leaching and acidification, and to the acidic nature of the granitic parent material, rather than to the tree species themselves. Statistically, no significant differences emerged in these solid-phase chemical properties among the different forest covers, a finding the authors link partly to the young age of more than half of the plantations, most of which were less than six years old.

Where the tree species did matter was in soil water content. Soils under eucalyptus and birch plantations were the driest, averaging 13 and 14 percent respectively, while soils under shrublands held the most water at 27 percent on average, with statistically significant differences. The intermediate values fell between 19 percent under walnut and 25 percent under pine. The ability of eucalyptus to extract large amounts of soil water is well documented, although some authors argue that eucalyptus water depletion is more a myth tied to poor plantation management than an inherent trait of the trees. Birch, meanwhile, has been shown to deplete topsoil moisture compared with conifers such as spruce. Both the birch and eucalyptus stands in this study were established over shallow soils of roughly 50 centimeters that had been burnt by a wildfire in 2019, and the authors suggest that the fire disturbance, the soil management for tree establishment, or the low organic matter content, which reduces water retention, could all explain the dry conditions. Indeed, the team detected a significant positive correlation between soil water content and soil organic matter.

The most striking result concerns microbial respiration, the rate at which soil organisms release carbon dioxide as they decompose organic matter. Soils under walnut plantations showed the highest respiration rates, averaging 1,440 plus or minus 97 parts per million of carbon dioxide per gram, while soils under eucalyptus showed the lowest, at 537 plus or minus 211 parts per million per gram. When the values for all deciduous broadleaf species were pooled together, respiration under eucalyptus was significantly lower than under the deciduous forests, with the coniferous pine values falling in between. Soil respiration correlated positively with soil organic matter, total nitrogen and total carbon, and walnut soils happened to contain the highest organic matter content at 20.9 percent, while eucalyptus soils had the lowest at 12.1 percent.

The walnut result carries an intriguing biochemical twist. Walnut leaf litter is rich in phenolic compounds that can inhibit Gram-positive bacteria but leave fungi unaffected, and fungi are the main drivers of respiration in forest soils. This selective pressure could favor a fungal-dominated community and boost carbon dioxide efflux. The eucalyptus result, by contrast, may reflect a different mechanism: previous studies have described a decrease in fungal dominance within eucalyptus plantations, which could explain the suppressed respiration rates. The eucalyptus plots had all been burnt in 2019, whereas the walnut plots had no recent fire history, but meta-analyses suggest that total soil respiration generally recovers to pre-fire values within about five years, and around three years for temperate forests, making the fire explanation less conclusive.

For the pine plantations, which represented the largest group with 30 samples, the researchers compared respiration across stands of different ages but found no significant differences, although average values tended to decline with tree longevity, from 991 plus or minus 69 parts per million per gram in 2 to 4 year old stands to 774 plus or minus 162 parts per million per gram in stands aged 40 to 45 years. A similar age-related decline has been reported in other coniferous plantations. The team also measured the activity of beta-glucosidase, a key enzyme in the carbon cycle that completes the final step of cellulose hydrolysis by converting cellobiose to glucose, but detected no significant differences among the forest covers, with average values ranging from 60 plus or minus 5 micrograms of p-nitrophenol per gram per hour under walnut to 31 plus or minus 15 under shrublands. The authors suggest that the limited variability in edaphic properties and the young age of most stands may explain the lack of differentiation in this enzyme activity.

Aluminium emerged as another defining feature of these soils. Exchangeable aluminium concentrations averaged between 4.7 and 7.43 centimoles per kilogram, representing between 63 and 90 percent saturation of the exchange complex, with practically all samples exceeding 60 percent saturation, a threshold indicative of alic soils that can limit plant growth. The highest saturation values appeared under shrublands at 90 percent, pines at 86 percent and chestnut at 83 percent, although these differences were not statistically significant. Despite this potentially toxic aluminium load, timber production in Galicia remains high within the temperate-humid region, likely because soil organic matter complexes aluminium into less toxic forms, and anions such as sulfate and fluoride can also bind aluminium and reduce its toxicity. The soils under chestnut, shrubland and pine showed the lowest concentrations of exchangeable calcium and magnesium, possibly reflecting the high demand these species place on these base cations to cope with aluminium stress, and the team detected a strong correlation between exchangeable calcium and magnesium across their samples.

When all the physicochemical and biological properties were analyzed together using redundancy analysis, no structural differences between forest covers were detected. The permutation test revealed that stand age was the only significant factor affecting soil properties, while wildfire events were marginally significant. Community location, altitude, tree species, parental rock and soil depth had no significant effect. The first component of the analysis explained 21.1 percent of the variability and was related to soil respiration, higher in samples with greater organic matter content. The authors acknowledge that their initial hypothesis, that tree species would drive the biggest differences between native broadleaf species and intensive plantations, was not fulfilled, most likely because the different ages of the stands acted as a confounding factor, and because the analyses were restricted to the solid soil phase, which is less sensitive to change than the soil solution.

The implications reach far beyond Galicia. Forest soils are crucial carbon sinks, both above and below ground, yet the soil section is still sometimes excluded from carbon pool estimations despite the enormous amount of carbon stored in it. As climate change sharpens the urgency of maximizing the carbon that healthy forest soils can fix, the finding that which tree species are cultivated measurably alters soil microbial respiration should be considered when elaborating forestry exploitation plans. Soils under eucalyptus exhibited the lowest values for both moisture and microbial respiration, while broadleaf deciduous species generally supported higher microbial activity through greater litter inputs and root exudation. The authors call for further research integrating microbial community analysis with functional assessments, alongside evaluating long-term wildfire and management impacts, to guide forest management under specific edapho-climatic conditions in a warming world.

Subject of Research: Forest soil science

Article Title: Effect of Different Tree Plantations on the Chemical Properties and Microbial Activity in Galician Forests Soils

Article References: Barreiro, A., Míguez-González, A., Cela-Dablanca, R., Díaz-Raviña, M., Núñez-Delgado, A., Fernández-Sanjurjo, M. J., & Álvarez-Rodríguez, E. (2025). Effect of Different Tree Plantations on the Chemical Properties and Microbial Activity in Galician Forests Soils. Spanish Journal of Soil Science, 15, Article 14988. https://doi.org/10.3389/sjss.2025.14988

Image Credits: AI Generated

DOI: 10.3389/sjss.2025.14988

Keywords: forest soils, soil respiration, carbon sink, eucalyptus, soil microbiology, forestry management, Galicia, wildfire, Effect, Different, Tree, Plantations

Calonectria species are serious business in plant pathology. With roughly 137 species recognized worldwide based on DNA sequence comparisons, the genus includes pathogens capable of infecting at least 611 plant species across 139 plant families. They cause leaf and shoot blight of Eucalyptus, one of the most economically important forestry crops in China, Southeast Asia, and South America, as well as red crown rot of soybean, black pod rot of peanut, and the devastating blight of boxwood ornamentals. The fungi survive in soil as thick-walled chlamydospores and microsclerotia, persisting for long periods even when no symptoms are visible above ground. At least 84 of the known species have been recovered from soils in Asia, Africa, North America, and South America, making reliable soil detection a cornerstone of both disease surveillance and quarantine efforts.

The traditional approach, in use for decades, involves scattering plant tissue or germinating seeds onto moistened soil and waiting for the fungi to sporulate on the bait surface, after which spores can be transferred to laboratory media. Germinating seeds of alfalfa, Medicago sativa, became the de facto standard after decades of use in studies around the world. Yet, as the authors of the new study point out, this convention rests more on habit than on evidence. Earlier bait evaluations were limited to one or a few baits, and most older studies identified isolates by morphology alone, leaving open the question of whether any given bait actually captures the full diversity of Calonectria lurking in a soil sample.

To close that gap, researchers assembled an ambitious experimental design spanning China’s climatic range. They collected forest soil from eight sites in five provinces and autonomous regions: Fujian and Hainan in the subtropical and tropical south, Heilongjiang in the cold temperate northeast, Henan in the warm temperate center, and Xizang in the subtropical west. From plantations and natural forests, they gathered soil from the surface down to a depth of 50 centimeters, ultimately testing a total of 1,040 isolation cups. Each cup received one of 26 baits: seeds of ten plant species, leaves of fourteen species, segments of soybean stem, and, in a nod to a quirky 1960 report, human hair, which a researcher named Griffin once used successfully to isolate the fungus.

The baits were chosen according to strict criteria. Each had either been used successfully in a previous study, come from a plant from which Calonectria had been isolated in nature, or belonged to a plant family known to host more than ten Calonectria species. Seeds had to be small enough, under five millimeters, to fit in an isolation cup and germinate within two days, and all baits needed to work within 15 days. Alfalfa seed was included as the positive control against which everything else would be judged. Every bait was surface disinfested in 75 percent ethanol, placed on the soil surface, and inspected daily under a dissection microscope for the characteristic conidiophores, the spore-bearing structures that signal a successful capture.

The results were striking. Calonectria appeared in 641 of the 1,040 cups, yielding 1,282 single-conidium isolates. Human hair, despite its historical pedigree, trapped nothing at all. Success rates for the remaining 25 baits ranged from 17.5 to 97.5 percent, with leaves of Rhododendron pulchrum outperforming even the alfalfa control. To identify what they had caught, the team sequenced up to four gene regions for each isolate: tef1, tub2, cmdA, and his3. All 1,282 isolates were first genotyped with tef1 and tub2, producing 41 combined genotypes, and 142 representative isolates were then sequenced across all four loci and subjected to maximum likelihood phylogenetic analysis against reference sequences from 57 known species.

The genetic analysis revealed eight species across three species complexes. Calonectria hongkongensis dominated the collection with 370 isolates, or 28.9 percent, followed by Ca. aconidialis at 21.4 percent, Ca. canadiana at 18.2 percent, Ca. pacifica at 14.1 percent, Ca. kyotensis at 12.2 percent, Ca. lichi at 2.7 percent, Ca. chinensis at 1.8 percent, and Ca. pseudoreteaudii at just 0.7 percent. Geography mattered: Ca. hongkongensis appeared only in Hainan and Fujian, Ca. canadiana in Heilongjiang and Henan, and all isolates of Ca. pacifica and Ca. kyotensis came from Fujian. Notably, statistical comparisons showed that bait performance was not significantly influenced by climatic zone, meaning the conclusions should hold across tropical, subtropical, and temperate forests alike.

The clearest pattern to emerge was that leaves beat seeds. The 14 leaf baits yielded an average of 6.5 species and 61 isolates each, compared with 5.1 species and 40.2 isolates for the 10 seed baits. Leaves of Dianthus caryophyllus and Saccharum officinarum each captured all eight species, and multiple-comparison tests confirmed that several leaf baits, including sugarcane, rose, acacia, carnation, camphor, fan palm, weeping fig, and rhododendron, recovered significantly more species and isolates than the weakest seed baits such as Chinese cabbage, zinnia, ryegrass, chia, garden balsam, and sesame. The best and worst performers differed dramatically: carnation leaves yielded 2.7 times more species and 3.8 times more isolates than zinnia seed. Among seeds, Lythrum salicaria, or purple loosestrife, matched alfalfa in the number of species detected and outperformed it for three species by genotype count, marking it as a viable alternative to the standard.

Perhaps the most consequential finding concerns Calonectria pseudoreteaudii, an important Eucalyptus leaf blight pathogen. This species was trapped by only four of the 26 baits, and leaves of Eucalyptus urophylla, the host itself, recovered the most isolates spanning multiple genotypes. The lesson is straightforward: when hunting a specific pathogen, baiting with tissues of its known host plant can dramatically improve detection. For surveying the genus as a whole, the authors recommend combining germinating seed of alfalfa or purple loosestrife with leaves from a variety of plants, including sugarcane, rose, fan palm, acacia, and rhododendron, and, wherever possible, adding foliage of the target host. Given the wide geographic and climatic spread of the soils tested, and the high species and genetic diversity recovered, the researchers argue that this combined baiting strategy should translate well to Calonectria surveys far beyond China’s borders.

Subject of Research: Comparative efficacy of plant baits for isolating soil-borne Calonectria fungi from Chinese forest soils

Article Title: A comparison of twenty-six baits for isolating Calonectria species illustrates differences in their efficacy and relevance

Article References: Zhou, H., Dong, H., Zhou, W., Wingfield, M. J., & Chen, S. (2026). A comparison of twenty-six baits for isolating Calonectria species illustrates differences in their efficacy and relevance. IMA Fungus, 17, Article e190896. https://doi.org/10.3897/imafungus.17.190896

Image Credits: AI Generated

DOI: 10.3897/imafungus.17.190896

Keywords: Calonectria, plant pathology, soil-borne fungi, baiting, forest soils, Eucalyptus, DNA barcoding, phylogenetics, Medicago sativa, fungus isolation, China, plant quarantine

The editorial, published in Volume 16 of the journal, was written by Alberto Enrique, Íñigo Virto, Avelino Núñez Delgado, Jorge Mataix-Solera, and Irene Ortiz-Bernad, researchers affiliated with Spanish universities including the Universidad Pública de Navarra, the Universidade de Santiago de Compostela, the Universidad Miguel Hernández de Elche, and the Universidad de Granada. They describe a scientist whose legacy was simultaneously scientific, educational, and institutional. Porta was a co-founder and Secretary of the Editorial Board of the Spanish Journal of Soil Science and served as President of the Spanish Society of Soil Science, an organization known by its Spanish acronym SECS. Perhaps most notably, he worked tirelessly to strengthen the connections between the Spanish and Latin American Soil Science Societies, building bridges across the Atlantic at a time when such collaboration was far from routine.

The special issue opens with a contribution by Alcañiz and colleagues that gathers personal and professional reflections from disciples, colleagues, and friends of Porta, offering an intimate portrait of a career that shaped generations of soil scientists. The tribute article reviews his pioneering work on salt-affected soils and gypsum-rich soils, two notoriously difficult materials that demand specialized analytical approaches, along with his contributions to soil mapping and the standardization of laboratory methods. Special emphasis is placed on his textbooks, which became foundational references for Spanish-speaking students, and on his international training initiatives that carried rigorous soil education far beyond Spain’s borders. His role in strengthening scientific institutions, journals, and the public dissemination of soil knowledge emerges as a defining thread of the tribute.

From this personal opening, the issue pivots to the kind of applied research Porta championed. Abbas and colleagues assessed the effects of biochar applied at three percent, combined with compost and animal manure at concentrations between 0.5 and 1 percent, on soil carbon fractions, soil properties, and maize growth in low-fertility soil. The results were striking: biochar combined with one percent compost significantly improved plant growth, soil organic matter, microbial biomass, and the carbon pool index, a metric that tracks how effectively soil stores and protects carbon. In an era when agriculture is under pressure to rebuild degraded soils while feeding a growing population, the findings position organic amendments as a sustainable strategy that simultaneously enhances crop productivity and supports a circular economy under changing climate conditions.

Water and salt management, topics close to Porta’s own research on salt-affected soils, feature prominently in the issue. Altés and colleagues analyzed salt dynamics and drainage loads in a newly established irrigation district in the Ebro basin in northeastern Spain between 2021 and 2023, a period that included the severe drought of 2023. By monitoring two sub-basins, the researchers found that a 31 percent reduction in irrigation delivery produced a 73 percent decrease in drainage and a 70 percent reduction in salt exports. The numbers carry a double message. On one hand, irrigation restrictions can dramatically improve water and salt management, preventing the salinization that has ruined farmland since antiquity. On the other hand, the restrictions came with associated yield losses, a reminder that every water management decision involves trade-offs between conservation and production.

Fire and vegetation management were also on the agenda. Quintana-Esteras and colleagues evaluated the effects of prescribed burning and selective shrub clearing on subalpine soils and vegetation in the Central Pyrenees, two techniques widely used to control shrub encroachment in mountain pastures. Both treatments similarly increased soil pH and reduced several physical and chemical properties, while microbial functional diversity remained stable, suggesting a degree of resilience in the soil microbial community. However, mechanical clearing enhanced soil microbial activity compared to burning, and two years after the interventions, shrub cover remained low in both treatments, although prescribed burning resulted in more bare soil and reduced plant diversity than selective clearing. For land managers weighing these options, the study offers a nuanced picture in which the gentler mechanical approach appears to preserve more of the ecosystem’s biological fabric.

Precision agriculture takes center stage in the work of Aguirre-Arcos and colleagues, who assessed sap analysis as a rapid diagnostic tool for the nutritional status of olive trees under integrated production in southern Spain. Across trials on five farms, the researchers documented clear seasonal nutrient fluxes in the sap, shaped by climate and the trees’ phenological stages. Comparisons among sap, leaf, and soil analyses highlighted the dominance of potassium in sap and revealed climate-driven variability in micronutrients. The technique does not replace traditional methods, but it complements them, supporting more precise and balanced fertilization strategies in olive orchards, an economically vital crop in the Mediterranean where over-fertilization wastes resources and under-fertilization erodes yields.

Two contributions underscore the cultural and institutional dimensions of soil science, areas where Porta’s influence was profound. Usón Murillo and colleagues analyzed initiatives to harmonize soil analytical methods in Spain through interlaboratory proficiency tests promoted by the Spanish Society of Soil Science and partner institutions. Results from tests conducted in 2019 and 2021 revealed significant methodological differences among laboratories, with only partial improvements in performance and persistent weaknesses, particularly in organic matter and texture analyses. The study makes a compelling case for regular proficiency testing, arguing that reliable soil data underpin sustainable soil management and effective policy implementation. Without comparable measurements, soil data cannot be aggregated, compared, or trusted at regional or national scales.

In an unexpected turn, Pérez Moreira and Barral Silva explored the rare but significant representation of soil in Western landscape painting, identifying periods of naturalistic art, particularly seventeenth-century Dutch painting and the nineteenth-century European landscape schools, when artists depicted soils with unusual detail. Some of these works reveal recognizable soil horizons and features that can be interpreted using modern soil science, effectively turning canvases into historical soil archives. The study contextualizes these artistic representations historically and culturally, illuminating the intersections between art, the observation of nature, and soil knowledge, and demonstrating that the scientific and humanistic study of land are not separate endeavors but parallel ways of reading the same surface.

The issue closes with two studies that tie the threads together. Barreiro and colleagues examined the influence of tree species on soil properties and microbial activity across 54 forest plantations in Galicia, northwestern Spain, finding generally acidic soils with high organic matter and low phosphorus contents. Moisture varied by vegetation, with the driest soils under eucalyptus and birch and the wettest under shrublands, while microbial respiration was highest in walnut soils and lowest under eucalyptus. The results carry direct implications for climate-adaptive forestry planning, since tree species selection shapes soil microbial function and carbon stabilization. Finally, Tierra and colleagues investigated soil salinity in the rainfed landscapes of the Saladas of Sástago-Bujaraloz in the Central Ebro Basin, analyzing 319 soil samples alongside electromagnetic sensor readings. They found highly variable and often extreme salinity, with 73 percent of samples classified as very strongly saline, and the strongest sensor correlations at depths of 0 to 100 centimeters. Their proposal to incorporate soil salinity as an agronomic criterion within the EU Common Agricultural Policy, recommending the exclusion of plots with electrical conductivity above 10 dS per meter, a threshold exceeded across more than half of their study area, shows how the science Porta devoted his life to can flow directly into European policy. Together, these contributions form a fitting memorial: a portrait of soil science as a living, interdisciplinary enterprise, from laboratory benches and olive groves to mountain forests, museum walls, and the halls of Brussels.

Subject of Research: A memorial special issue of Spanish soil science research honoring soil scientist Jaume Porta Casanellas

Article Title: Editorial: Jaume Porta Casanellas – RENS Soil Science

Article References: Enrique, A., Virto, Í., Delgado, A. N., Mataix-Solera, J., & Ortiz-Bernad, I. (2026). Editorial: Jaume Porta Casanellas – RENS Soil Science. Spanish Journal of Soil Science, 16, Article 16319. https://doi.org/10.3389/sjss.2026.16319

Image Credits: AI Generated

DOI: 10.3389/sjss.2026.16319

Keywords: soil science, Jaume Porta Casanellas, Spanish Journal of Soil Science, soil salinity, biochar, soil organic matter, prescribed burning, olive trees, interlaboratory proficiency testing, forest soils, soil education, Ebro basin

The team, led by Maisy Roach-Krajewski and corresponding author Jérôme Laganière at the Laurentian Forestry Centre in Québec, screened an extraordinary 4,338 records drawn from Scopus, EBSCO, OpenAlex, Google Scholar, and government repositories in Canada and the United States. After applying strict eligibility criteria, they distilled the literature down to 72 primary studies published between 1996 and 2025. Each study was coded across disturbance type, biome, sensor platform, spatial scale, and soil degradation indicator, producing a structured map of nearly three decades of research effort. The result is less a single discovery than a diagnostic of an entire field: a candid accounting of what orbiting and airborne sensors can honestly tell forest managers about the ground below.

The headline finding is a stark imbalance. Wildfire accounts for just over half of the disturbance cases in the evidence base, and harvesting for nearly 43 percent, while insect outbreaks, windthrow, mining, and off-road vehicle use barely register. This skew is not an accident of research fashion. Wildfire strips away canopy and leaves behind ash, char, and exposed mineral soil, producing strong, spatially coherent spectral contrasts that multispectral sensors detect with high confidence. Harvesting, by contrast, leaves discontinuous scars such as ruts, skid trails, and landings that demand very-high-resolution three-dimensional sensing. In other words, the literature clusters around disturbances that create visible surface signals, because those are the signals remote sensing can actually read.

Technically, the evidence map reveals two distinct methodological worlds. In post-fire landscapes, multispectral satellite data, especially from Landsat and Sentinel-2, dominate. Spectral indices built on shortwave infrared bands are particularly valuable because their sensitivity to moisture and char allows researchers to discriminate among burn severity classes across landscapes spanning up to more than 1.4 million hectares. In harvested forests, the toolset flips toward structure rather than spectra: LiDAR and stereo photogrammetry, increasingly deployed from unmanned aerial vehicles, reconstruct rut geometry, surface displacement, and microtopography in fine detail. UAV-based approaches only entered the literature after 2013, and harvesting studies did not appear at all until 2012, revealing how recently this second world has taken shape.

The authors organize these patterns through a disturbance–threat–indicator framework that classifies observability as direct, proxy-based, or limited. Burn severity after wildfire is directly observable, since combustion residues and exposed soil produce measurable spectral signatures. Soil compaction after harvesting, one of the most consequential threats to site productivity, is only proxy-observable: sensors can map rut geometry and surface roughness, but the actual loss of porosity and hydraulic conductivity beneath the surface must be confirmed with field measurements. Indicators such as bulk density, soil organic carbon stocks, nutrient pulses, pH, and microbial community shifts remain almost entirely beyond remote detection in forested settings, where canopy and understory occlusion block the view that agricultural systems, with their seasonal bare-soil exposure, do not face.

Timing emerges as a critical constraint throughout the synthesis. Surface-expressed signals are transient. Ash and char contrasts fade as vegetation regrows and moisture cycles shift spectral values independently of any real change in soil condition. The evidence map shows that most studies acquire imagery in the same year as the disturbance, and that pre-disturbance baselines, essential for spectral differencing techniques such as dNBR, are reported almost exclusively for wildfire cases, where decades of satellite archives make before-and-after comparison cheap and standardized. Harvesting studies, lacking comparable high-resolution pre-event baselines, typically map post-event footprints and infer subsurface condition through targeted field sampling rather than true change detection.

Scale introduces its own trade-offs. Broad-footprint outcomes such as soil burn severity and post-fire erosion pair naturally with satellite systems that maximize coverage and comparability, with wildfire study areas averaging nearly 150,000 hectares. Narrow, discontinuous outcomes such as rutting and displacement demand UAV or terrestrial platforms that deliver diagnostic detail at the cost of coverage efficiency. The most promising operational design, and one increasingly visible in the literature, is nested: regional satellite screening identifies high-risk areas, then targeted drone or LiDAR surveys quantify mechanisms where management action is most needed. This hybrid logic preserves regional consistency while capturing the site-scale resolution that mitigation decisions require.

The study is equally candid about its own limits and those of the field. Geographically, the evidence base is concentrated in Europe and North America, with boreal and Mediterranean biomes best represented and tropical forests nearly absent, a gap the authors attribute partly to persistent cloud cover that can leave months-long holes in optical satellite records. The search strategy itself, weighted toward forestry terminology, likely undercounted chemically framed degradation pathways in mining contexts. Compound disturbances, particularly salvage logging after fire, remain poorly understood despite evidence that their soil impacts are non-additive, amplifying erosion risk and delaying recovery beyond what either disturbance would cause alone.

Looking forward, the authors identify emerging technologies that could push against current observability limits. Hyperspectral sensors capture narrow spectral features tied to mineralogy, organic matter, and ash composition, strengthening proxy relationships for soil carbon and nutrient change. Quantum gravity gradiometers, demonstrated in laboratory and field trials, could eventually detect subsurface density contrasts such as compaction or buried voids that no optical or LiDAR system can reach. Artificial intelligence and multi-sensor fusion promise to integrate structural, spectral, and radar data streams to detect harvesting damage under partial canopy. None of these are yet operational, but together they sketch a future in which the invisible fraction of soil degradation shrinks.

The practical message for forest agencies is sobering but clarifying. Remote sensing is not a replacement for field measurement; it is a stratification and decision-support layer that tells field crews where to look and helps translate scattered ground truth into landscape-scale understanding. As reporting frameworks such as the FAO Global Forest Resources Assessment demand transparent, repeatable, indicator-driven soil metrics, this evidence map provides something the field has lacked: an honest inventory of which indicators can be consistently observed from above, which require proxy reasoning with explicit calibration, and which will always demand boots on the ground. In an era when an estimated one-third of global soils are already degraded and forests face intensifying disturbance regimes, knowing the limits of our orbital eyes may be as valuable as extending their reach.

Subject of Research: Remote sensing of post-disturbance soil degradation in forest ecosystems

Article Title: Post-disturbance soil monitoring in forests using remote sensing: an evidence map

Article References: Roach-Krajewski, M., Giroux-Bougard, X., Paré, D., Dallaire, C., Guindon, L., Jordan, F., Norris, C., Webster, K., & Laganière, J. (2026). Post-disturbance soil monitoring in forests using remote sensing: an evidence map. SOIL, 12(2), 885-914. https://doi.org/10.5194/soil-12-885-2026

Image Credits: AI Generated

DOI: 10.5194/soil-12-885-2026

Keywords: remote sensing, forest soils, soil degradation, wildfire, forest harvesting, LiDAR, photogrammetry, burn severity, soil compaction, evidence map, satellite monitoring, forest management

For much of the history of soil science, researchers assumed that the slow decay of tough plant compounds such as lignin was the main route by which organic matter accumulated in soils. That view has been overturned in the past decade. Today, a growing body of evidence indicates that a large share of stable soil organic carbon is not plant material at all, but the residues of dead microorganisms, often called microbial necromass or microbial residue carbon. Microbes consume plant litter, build their own biomass, and when they die, their cell walls and other structural molecules bind to soil minerals and persist far longer than most raw plant debris. This pathway, sometimes described as the microbial carbon pump, effectively converts labile plant carbon into a more durable form. Understanding what controls the pump has become a central question for scientists trying to predict how soils will respond to climate change and shifting vegetation.

The research team set out to answer that question by comparing three types of forest stands: broadleaved forests, coniferous forests, and mixed forests. In each, they measured the chemical quality of the leaf litter, the total soil organic carbon content and its various fractions, and two powerful molecular fingerprints of carbon origin. Amino sugars served as markers for microbial residues, allowing the researchers to distinguish carbon left behind by bacteria from carbon left behind by fungi. Lignin phenols, meanwhile, acted as tracers of plant-derived carbon and revealed how far the lignin in the litter had been degraded. To probe the nutritional state of the microbial communities, the team applied an ecological stoichiometric approach, which evaluates whether microbes are limited more by carbon, nitrogen, or phosphorus based on the balance of these elements in their environment.

The results revealed a striking pattern. Broadleaved forest litter contained the lowest lignin content and the least carbon lability, meaning its carbon was less readily decomposable, but it boasted the highest levels of nitrogen, phosphorus, and cellulose, as well as the highest ratio of nitrogen to lignin. These stands also showed the greatest microbial nitrogen limitation, the highest total soil organic carbon, and, crucially, the largest accumulations of microbial residue carbon, including both bacterial residue carbon and fungal residue carbon. Lignin phenol concentrations and the degree of lignin degradation were likewise highest under broadleaved trees. In other words, the forests with the most nitrogen-rich, easily digestible litter were the ones where microbes were working hardest, dying in greatest numbers, and leaving the most residue behind.

Across all three stand types, the researchers observed that microbial residue carbon and plant residue carbon accumulated in step with total soil organic carbon, suggesting that both sources contribute synchronously to the growing carbon pool rather than one simply replacing the other. To identify which factors mattered most, the team used random forest analysis, a machine learning technique that ranks the influence of many variables simultaneously. The verdict was unambiguous: litter nitrogen emerged as the primary driver of microbial residue carbon accumulation, outweighing other litter characteristics such as lignin content or carbon lability.

But correlation alone does not establish mechanism, so the researchers turned to structural equation modeling, a statistical framework that allows scientists to test hypothesized chains of cause and effect. The model supported a compelling sequence. Higher litter nitrogen intensified the microbial nitrogen limitation, and that intensified limitation in turn promoted the accumulation of microbial residue carbon. This may seem counterintuitive at first glance: why would nitrogen limitation stimulate carbon storage? The likely explanation lies in microbial physiology. When nitrogen-rich litter raises the nitrogen supply relative to microbial demand, it spurs microbial growth and activity, and microbes constrained by nitrogen must invest more effort in acquiring it, processing more carbon in the process and building more biomass that eventually becomes residue. The nitrogen limitation detected by the stoichiometric analysis thus reflects a dynamic, growth-driven system in which abundant nitrogen fuels the microbial engine that converts plant carbon into persistent soil carbon.

The study also traced the consequences of this microbial activity for the composition and stability of the soil carbon pool. The accumulation of microbial residue carbon, and particularly bacterial residue carbon, increased the content of recalcitrant organic carbon, the fraction of soil organic carbon that resists decomposition. At the same time, this shift reduced the overall carbon lability of the soil, meaning a smaller proportion of the carbon pool was readily available for microbes to respire back into the atmosphere as carbon dioxide. In practical terms, nitrogen-rich broadleaved litter did not just add more carbon to the soil; it changed the character of that carbon, steering it toward a more stable, longer-lived form. This is a critical distinction, because the climate value of soil carbon depends not only on how much is stored but on how long it stays stored.

The implications extend well beyond forest ecology. As governments and land managers around the world pursue afforestation and reclamation programs to sequester carbon, the choice of tree species is often made on the basis of growth rates and timber value. This study suggests that litter chemistry deserves equal attention. Planting or encouraging nitrogen-rich broadleaved species could enhance the microbial carbon pump, boosting both the quantity and the stability of soil organic carbon. Conversely, stands dominated by conifers, whose litter is lignin-rich and nitrogen-poor, may build soil carbon more slowly and in a less stable form. In mixed forests, the researchers found intermediate patterns, hinting that species composition within a stand can be tuned to manage below-ground carbon dynamics. Such insights could inform everything from carbon credit accounting to the restoration of degraded soils.

The work also adds nuance to a long-running scientific debate about the role of nitrogen in decomposition. Nitrogen limitation of decay has been documented in many ecosystems, and some researchers have argued that it slows the breakdown of organic matter, potentially preserving soil carbon. The new findings suggest a more intricate picture: nitrogen availability shapes not only how fast litter decomposes but how effectively the products of decomposition are funneled into microbial biomass and, ultimately, into stable necromass. The microbial carbon pump, in this view, is throttled by the nitrogen supply in the litter, and managing that supply is a lever for managing soil carbon. As the authors conclude, shifts in stand type alter litter nitrogen, which primarily regulates soil organic carbon sequestration through this microbial pathway.

There remain open questions. The study was conducted across forest stands of different types, and future work will need to test whether the same relationships hold across climates, soil types, and timescales, and how disturbances such as fire, harvesting, or warming might disrupt the nitrogen-microbe-carbon chain. Data from the study will be made available on request, and the research was supported by funding from Chinese national and provincial science programs. For now, the message is clear and quietly profound: the fate of carbon in forest soils rests substantially on the shoulders of microscopic organisms, and what those organisms accomplish depends on the chemistry of the leaves that fall above them. A forest’s legacy in the soil, it turns out, is written as much in the nitrogen of its litter as in the wood of its trees.

Subject of Research: The role of litter nitrogen in regulating soil organic carbon sequestration through microbial residue carbon accumulation in forest soils

Article Title: Litter nitrogen drives soil organic carbon sequestration by promoting microbial residue carbon accumulation

Article References: Zhang, M., Li, H., Wang, Y., Cui, Y., Gao, Y., Jia, Y., Yu, H., Dong, Q., Wang, Y., & Xu, Z. (2026). Litter nitrogen drives soil organic carbon sequestration by promoting microbial residue carbon accumulation. Plant and Soil. https://doi.org/10.1007/s11104-026-09109-y

Image Credits: AI Generated

DOI: 10.1007/s11104-026-09109-y

Keywords: soil organic carbon, microbial residue carbon, litter nitrogen, microbial carbon pump, forest soils, broadleaved forests, coniferous forests, lignin, amino sugars, ecological stoichiometry, carbon sequestration, microbial necromass

The research, led by Jia Yao and Ming Nie of Fudan University in Shanghai, together with colleagues, tackled a question with direct implications for climate modeling. Soil microbial respiration releases carbon dioxide as microbes metabolize organic matter, and the rate of that release accelerates as temperatures rise. The magnitude of this acceleration is captured by the temperature sensitivity coefficient, or Q10, which describes how much respiration increases for every ten degrees Celsius of warming. Whether Q10 varies systematically across climates, and what biological mechanisms drive that variation, remains one of the more contested issues in terrestrial carbon cycle science, with direct consequences for how strongly soils are expected to feed back into atmospheric warming.

To probe the role of lysogenic viruses, the team collected soils from 13 forest sites distributed along a 3,600-kilometer latitudinal climate gradient across China, from cool northern forests to warm subtropical ones. In the laboratory, they incubated each soil at three temperatures, 15, 25, and 35 degrees Celsius, and measured microbial respiration. Crucially, they also employed a chemical trick that has become a standard tool in viral ecology: treatment with mitomycin C, a compound that damages bacterial DNA and thereby provokes temperate prophages harbored within bacterial genomes to enter the lytic cycle. The response of a soil community to mitomycin C induction serves as an operational proxy for the abundance and activity of lysogenic viral processes in that community.

The design allowed the researchers to construct three distinct estimates of thermal sensitivity. Soils treated with mitomycin C exhibited higher Q10 values than untreated controls, indicating that chemically forcing prophages out of their lysogenic state intensified the temperature response of respiration. More intriguing was a third quantity: the Q10 calculated from the contrast between induced and uninduced soils, which the authors interpret as an SLV-associated Q10, reflecting the thermal behavior of respiration linked to lysogenic viral processes. This proxy-derived sensitivity was the lowest of the three, suggesting that processes tied to lysogenic viruses are associated with a dampened apparent response of respiration to warming.

Across the 13 sites, the variation in this SLV-associated temperature sensitivity was most strongly associated with two characteristics of the bacterial communities: their abundance and their life-history strategies. Soil bacteria are commonly sorted along a spectrum from r-strategists, which grow rapidly and opportunistically when resources are plentiful, to K-strategists, which invest in persistence, resource efficiency, and stress tolerance under more competitive conditions. Previous work has shown that the dominance of one strategy or the other shapes how microbial respiration responds to temperature, and the new findings indicate that the viral induction response is entangled with this same axis of microbial life history. Communities where lysogenic processes left a distinct imprint on respiration were also communities whose compositional and functional makeup reflected particular positions along the r-to-K spectrum.

Climate itself did not disappear from the picture, but its influence was largely indirect. The researchers used structural equation modeling, a statistical framework that allows direct and indirect pathways among variables to be separated, to trace how climatic variables propagate to the viral-linked temperature sensitivity. The analysis revealed that climate was connected to the SLV-associated Q10 through mediating factors, chiefly soil pH and the physical properties of the soil, such as texture-related characteristics. This pattern is consistent with a growing body of viral ecology showing that soil pH is a powerful determinant of viral community structure at scales from local plots to the globe. In other words, climate appears to set the stage, through the chemical and physical environment it helps create, on which lysogenic viral processes and bacterial life-history traits together govern how temperature-sensitive respiration becomes.

The geographic pattern embedded in these results is especially noteworthy. The association between the mitomycin C response and reduced apparent thermal sensitivity was strongest in warmer forest soils, implying that in the very ecosystems where microbial respiration could potentially release the most additional carbon under continued warming, lysogenic viral processes may be exerting a moderating influence. The authors are careful with their language throughout, framing the findings in terms of association rather than proof of causation. Mitomycin C induction is a blunt instrument: the compound is a DNA-damaging agent, and the observed differences between treated and untreated soils could in principle reflect the combined consequences of prophage induction, bacterial mortality, altered community composition, and the release of cellular contents. The interpretation of the induced contrast as an SLV-associated signal is therefore an operational one, a proxy rather than a direct measurement of viral behavior.

Even so, the study lands at a moment when the viral dimension of soil carbon cycling is moving rapidly from the margins to the mainstream. A global atlas of soil viruses published in 2024 catalogued an enormous and previously uncharted viral diversity and flagged potential biogeochemical impacts, while other recent work has demonstrated that viral lysis can alleviate microbial nutrient limitation and accumulate chemically recalcitrant dissolved organic matter in soils. Theoretical treatments have argued that viral infections likely mediate microbial controls on ecosystem responses to warming, but empirical tests along real climate gradients have been scarce. By combining a standardized induction assay with controlled incubations across thousands of kilometers, the new study offers one of the more systematic empirical links to date between a specific viral strategy and a keystone carbon-cycle parameter.

The mechanistic possibilities behind the observed pattern remain open. Lysogeny can benefit bacterial hosts directly: cryptic prophages can confer tolerance to environmental stress, and integrating viruses may alter host metabolism in ways that change growth rates and resource use. If lysogeny is more prevalent or more consequential in warm, low-latitude soils, and if it favors or co-occurs with K-strategist lineages whose respiration is inherently less temperature responsive, then the dampened SLV-associated Q10 would follow as an emergent property of the host-virus ecosystem. Alternatively, the induction treatment itself may reveal the scale of the lysogenic reservoir, with soils harboring more temperate phages showing different post-induction respiratory trajectories. Distinguishing among these mechanisms will require experiments that go beyond induction proxies, perhaps tracking viral and host population dynamics through time under warming.

For climate modelers, the message is both cautionary and constructive. The findings suggest that bacterial responses associated with lysogenic viral processes deserve a place in future assessments of how forest soil carbon responds to warming, particularly when evaluating microbial controls on carbon turnover. If lysogeny-associated processes genuinely reduce the thermal sensitivity of respiration in warmer forests, then current projections that ignore viral regulation may overestimate carbon losses from those systems. But because the evidence is associative and proxy-based, the authors’ conclusions point less toward immediate model revision and more toward an agenda: combining induction experiments with viromics, microbial trait measurements, and gradient sampling to pin down when, where, and how the quiet passengers in bacterial genomes bend the temperature curve of one of Earth’s largest carbon fluxes. The forest floor, it turns out, is not merely a chemical reactor warmed by the atmosphere above; it is also an arena where viruses, hosts, and climate quietly negotiate the pace of carbon’s return to the sky.

Subject of Research: Association between lysogenic soil viruses and the temperature sensitivity of forest soil microbial respiration

Article Title: Lysogenic viral processes are associated with reduced temperature sensitivity of forest soil microbial respiration

Article References: Yao, J., Xu, J., Xu, X., Liu, M., Chen, C., Bao, Y., Li, J., & Nie, M. (2026). Lysogenic viral processes are associated with reduced temperature sensitivity of forest soil microbial respiration. Plant and Soil. https://doi.org/10.1007/s11104-026-09126-x

Image Credits: AI Generated

DOI: 10.1007/s11104-026-09126-x

Keywords: lysogeny, soil viruses, bacteriophages, forest soils, microbial respiration, temperature sensitivity, Q10, carbon cycle, climate gradient, mitomycin C, bacterial life-history strategies, climate warming

The team collected soil samples from seven representative land uses in tropical Thailand and applied a technique known as density fractionation, which physically separates soil organic matter into pools of differing stability. Free particulate organic matter, the lightest fraction, represents fresh plant debris that decomposes rapidly. Occluded light organic matter is the same kind of material but physically sheltered inside soil aggregates, protected from microbes by architecture rather than chemistry. Weakly bound and strongly bound fractions, by contrast, represent organic matter attached to mineral surfaces, with the strongly bound pool generally considered the most persistent reservoir of carbon in soil.

When the researchers measured total soil organic carbon across the seven land uses, pasture emerged as the unexpected champion, holding 18.5 grams of carbon per kilogram of soil—more than forest, cassava plantation, or orchard. This result challenges the intuitive assumption that natural forest always stores the most carbon. Perennial grasses and their deep, dense root systems continuously deliver organic inputs below ground, where they are more likely to encounter minerals and become stabilized. The finding echoes a growing body of evidence that managed grasslands can be powerful allies in soil carbon accumulation, provided grazing and management pressures remain moderate.

Yet the distribution of carbon among fractions told a more nuanced story. Forest soils contained the highest carbon contents in the free particulate, occluded light, and weakly bound fractions, ranging from 1.26 to 2.37, 0.57 to 2.33, and 1.24 to 4.52 grams of carbon per kilogram of soil respectively. This pattern reflects the forest’s abundant litterfall and undisturbed aggregate structure, which together feed and shield organic matter across multiple protection mechanisms. In contrast, the strongly bound fraction—the long-term vault of soil carbon—was richest under pasture and cassava plantation, reaching between 6.66 and 10.63 grams of carbon per kilogram of soil. In these managed systems, carbon appears to be channeled preferentially into mineral associations, the pathway most likely to survive decades of microbial attack.

To understand the chemistry behind these patterns, the team turned to X-ray photoelectron spectroscopy, a surface-sensitive technique more commonly associated with materials science and catalysis research than with dirt. XPS bombards a sample with X-rays and measures the electrons ejected, revealing the elemental composition and chemical bonding environments of the outermost atomic layers. Applied to soil organic matter fractions, it allows scientists to distinguish aliphatic carbon—long hydrocarbon chains of the kind found in plant waxes, cutin, and suberin—from oxygen-rich functional groups such as ethers, alcohols, and carboxylic acids.

The spectroscopic results were striking. Across bulk soil and the free particulate, weakly bound, and strongly bound fractions, aliphatic carbon dominated the carbon signal. This is chemically significant because aliphatic compounds are notoriously resistant to decomposition; their waxy, hydrophobic structures make them poor food for microbes and help them persist in soil far longer than more labile, oxygen-rich molecules. The accumulation of aliphatic carbon in tropical soils is consistent with earlier observations that aliphatic compounds build up with increasing mean annual temperature, suggesting that in hot climates, chemical recalcitrance of these molecules becomes an especially important stabilizing force.

The occluded light fraction broke the pattern. Organic matter trapped inside soil aggregates was enriched in ether and alcohol carbon, and possibly carboxylic carbon—more oxidized, oxygen-bearing functional groups. The researchers attribute this to physical protection: sealed within aggregates, these otherwise decomposable compounds escape microbial enzymes not because of their chemistry but because of their address. The finding underscores that physical and chemical protection mechanisms operate on different subsets of the soil carbon pool, and that a complete picture of carbon persistence requires examining both.

For tropical agriculture, the practical message is provocative. Management practices that enhance inputs of aliphatic carbon-rich organic material—such as returning crop residues, applying organic amendments rich in waxes and suberin-like biopolymers, or maintaining deep-rooted perennial vegetation—may be particularly effective at boosting long-term carbon sequestration in tropical agricultural landscapes. Because tropical soils are warm and biologically active year-round, they rapidly consume labile organic matter; only chemically robust inputs and mineral-protected pools stand much chance of accumulating. The pasture result reinforces this logic, pointing to grassland restoration and improved pasture management as underappreciated climate tools in the tropics.

The study also carries a caution for land conversion. Forests excel at building the faster-cycling fractions—free particulate and occluded organic matter—that respond quickly to management and disturbance. When forests are cleared for intensive cultivation, these vulnerable pools are typically the first to be lost, releasing carbon within years to decades. The strongly bound mineral-associated pool, while more durable, depends on continuous replenishment and favorable mineralogy. Abandoned land, meanwhile, offers a natural experiment in recovery: as vegetation returns, carbon begins rebuilding through the particulate fractions before gradually transferring into more stable pools, a process that restoration initiatives worldwide hope to accelerate.

As nations refine their carbon accounting and pursue soil-based climate solutions under frameworks such as the 4 per mille initiative, studies like this one provide the mechanistic granularity needed to make those pledges credible. By pairing physical fractionation with X-ray photoelectron spectroscopy, the Thai team has shown that the fate of carbon in tropical soils is written in chemistry as much as in land management—and that the molecules farmers choose to leave behind may matter as much as the trees they choose to plant.

Subject of Research: Land use effects on soil organic matter stabilization and chemistry in tropical soils

Article Title: Land use shapes soil organic matter stabilization and chemistry in tropical soils: insights from density fractionation and X-ray photoelectron spectroscopy

Article References: Sonsri, K., Janplang, B., Phankamolsil, Y., Supruangnet, R., & Phankamolsil, N. (2026). Land use shapes soil organic matter stabilization and chemistry in tropical soils: insights from density fractionation and X-ray photoelectron spectroscopy. Environmental Science and Pollution Research. https://doi.org/10.1007/s11356-026-38210-z

Image Credits: AI Generated

DOI: 10.1007/s11356-026-38210-z

Keywords: soil organic matter, tropical soils, land use, carbon sequestration, density fractionation, X-ray photoelectron spectroscopy, aliphatic carbon, soil organic carbon, pasture, forest soils, mineral-associated organic matter, soil aggregates