Open research questions in Soil Carbon and Nitrogen Dynamics

What the literature leaves open

• ABSTRACT Conventional tillage in tropical and semiarid regions accelerates the degradation of soil functions, yet the cumulative impacts of Conservation agriculture on the physical, chemical, and biological dimensions of soil quality remain insufficiently integrated within unified analytical frameworks.

  Conservation Agriculture Improves Soil Resilience by Integrating Physical, Chemical, and Biological Pathways · 2026 · DOI

• Abstract Background Nitrogen deposition significantly alters carbon and nitrogen cycling in terrestrial ecosystems, yet how microbial network restructuring drives extracellular enzyme activity changes under continuous nitrogen input remains elusive.

  6-year nitrogen addition alters fungal network structure and extracellular enzyme activities in alpine grasslands: divergent responses between rhizosphere and bulk soils · 2026 · DOI

• Although biochar has been proposed as a potential approach to improve soil carbon storage, its effects on soil CO 2 efflux and associated soil–plant responses remain uncertain, especially in subtropical plantation forests and over longer observation periods.

  Contrasting first-year and tenth-year responses of soil CO2 efflux and soil carbon storage indicators to biochar addition in plantation forests · 2026 · DOI

• Acid-modified biochar offers a promising approach for improving the fertility of saline-alkali soils, yet the effects of its combined application with N fertilizer on SOC fractions and soil quality remain insufficiently studies.

  Acid-modified biochar combined with reduced nitrogen fertilizer improves soil organic carbon and cotton yield in saline-alkali soil · 2026 · DOI

• and mechanisms, Arch. Agron. Soil Sci., 65, 1446–1459, https://doi.org/10.1080/03650340.2019.1566713, 2019. in desert soils: Species, Autret, B., Mary, B., Chenu, C., Balabane, M., Girardin, C., Bertrand, M., Grandeau, G., and Beaudoin, N.: Alternative arable cropping systems: A key to increase soil organic carbon storage? Results from a 16 year field experiment, Agr. Ecosyst. Environ., 232, 150–164, https://doi.org/10.1016/j.agee.2016.07.008, 2016. Autret, B., Guillier, H., Pouteau, V., Mary, B., and Chenu, specific mineralization rates of organic car- C.: Similar bon and nitrogen in incubated soils under contrasted arable cropping systems, Soil Till. Res., 204, 104712, https://doi.org/10.1016/j.still.2020.104712, 2020. Bellone, D., Jeuffroy, M.-H., Bertrand, M., Mistou, M.-N., Barbu, C., Ballini, E., Morison-Valantin, M., Gauffreteau, A., and Pashalidou, F. G.: Are innovative cropping systems less dependent on synthetic pesticides to treat Septoria leaf blotch (Zymoseptoria tritici) than conventional systems?, Crop Prot., 170, 106266, https://doi.org/10.1016/j.cropro.2023.106266, 2023. Blanchy, G., Deroo, W., De Swaef, T., Lootens, P., Quataert, P., Roldán-Ruíz, I., Versteeg, R., and Garré, S.: Closing the phenotyping gap with non-invasive belowground field phenotyping, SOIL, 11, 67–84, https://doi.org/10.5194/soil-11-67-2025, 2025. Castellini, M. and Ventrella, D.: Impact of conventional and minimum tillage on soil hydraulic conductivity in typical cropping system in Southern Italy, Soil Till. Res., 124, 47–56, https://doi.org/10.1016/j.still.2012.04.008, 2012. Çelik, ˙I., Günal, H., Acir, N., Barut, Z. B., and Budak, to compare tillage systems M.: Soil quality assessment SOIL, 12, 703–714, 2026 https://doi.org/10.5194/soil-12-703-2026 O. Fülöp et al.: Electrical conductivity as proxy for soil microbial activity 713 in Cukurova Plain, Turkey, Soil Till. Res., 208, 104892, https://doi.org/10.1016/j.still.2020.104892, 2021. Chabert, A. and Sarthou, J.-P.: Conservation agriculture as a promising trade-off between conventional and organic agriculture in bundling ecosystem services, Agr. Ecosyst. Environ., 292, 106815, https://doi.org/10.1016/j.agee.2019.106815, 2020. Colas, E.: Impact de l’humidité et des solutions salines sur du Buntsandfrançaises, le comportement stein, Le moteur de https://doi.org/10.70675/96ade2f0z6a11z48faza984z3ae9b0ef3c0f, 2011. recherche des dimensionnel thèses grès de Cosentino, D., Chenu, C., and Le Bissonnais, Y.: Aggregate stability and microbial community dynamics under drying–wetting cycles in a silt loam soil, Soil Biol. Biochem., 38, 2053–2062, https://doi.org/10.1016/j.soilbio.2005.12.022, 2006. Crawford, R. L.: Microbial Diversity and Its Relationship to Planetary Protection, Appl. Environ. Microb., 71, 4163–4168, https://doi.org/10.1128/AEM.71.8.4163-4168.2005, 2005. Crowther, T. W., Van Den Hoogen, J., Wan, J., Mayes, M. A., Keiser, A.

  Electrical conductivity measurements as proxies for diffusion-limited microbial activity in soils under controlled laboratory conditions · 2026 · DOI

• Results demonstrate that the nutrient composition of organic materials varies widely, reflecting differences in source or origin of the material, feeding routines for animal-based organic materials, soil fertility status for plant-based materials as well as handling and storage practices (34).

  Nutrient composition and release patterns of selected organic materials: a guide for direct application and use in fertilizer formulations · 2026 · DOI

• However, the relative importance of biotic and abiotic drivers of CUE variations remains debated, resulting in large uncertainties in SOC predictions.

  Fungal community shifts driven by soil substrate availability govern microbial carbon use efficiency across an elevation gradient in the Qinling Mountains, China · 2026 · DOI

• This study had a two-year experiment period, which is insufficient to capture the long-term effects of conditioners (e.g., biochar, microbial fertilizer) on soil carbon pools and microbial communities. Moreover, the study focused only on wheat without incorporating the typical wheat–maize rotation system in southern Henan, limiting the generalizability of the conclusions. Future studies should implement long-term field experiments, include the rotation system, and expand to more regions and soil types to further validate the applicability of the conditioners, thereby enhancing the scientific rigor and generalizability of the findings. Author Contributions: Conceptualization and writing—original draft preparation, Xu Dongzhi; methodology, Zhang Weina; formal analysis, Wang Han and Jiang Bingshen; writing—review and editing, Liang Changli, Sun Hongmei, and Cao Lianbin; funding acquisition, Liu Junhe. All authors have ARTICLE IN PRESS ARTICLE IN PRESS ACCEPTED MANUSCRIPT read and agreed to the published version of the manuscript. Funding: This study was financially supported by the Key Research and Development Program of Henan Province (231111320300), National Natural Science Foundation of China (32301699), Joint Fund for Science and Technology Research and Development of Henan Province (242103810011). We also acknowledge the financial support from Huanghuai University Young Backbone-teacher funding program to Weina Zhang. Data Availability Statement: The datasets used and/or analyzed during the current study are available from the corresponding author upon reasonable request. Declaration of competing interest: The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper.

  Dual effects of soil conditioners on wheat yield and soil properties in southern henan · 2026 · DOI

• Biochar functions as a selective microbial habitat modifier offering new opportunities for precision microbiome engineering in saline-alkali agroecosystems, but specific strategies for such engineering require development.

  Contrasting acidic and alkaline biochar reprogram alfalfa metabolism and rhizosphere microbiomes in saline-alkali soils · 2026 · DOI

• The greater dosage sensitivity of AC-biochar producing inhibitory effects at higher addition rates is attributed to salt release, pH perturbation, or microstructural alterations, but the relative contribution of each factor remains unclear.

  Contrasting acidic and alkaline biochar reprogram alfalfa metabolism and rhizosphere microbiomes in saline-alkali soils · 2026 · DOI

• The quality–resilience trade-off observed with AC-biochar at higher doses suggests the need to optimize dosage to prevent diminished forage quality while maintaining stress defense activation.

  Contrasting acidic and alkaline biochar reprogram alfalfa metabolism and rhizosphere microbiomes in saline-alkali soils · 2026 · DOI

• The characteristics of ecoenzymatic stoichiometry exhibited dis- tinct patterns under different tree species plantations after the clear- cutting of E. robusta plantations. All data points positioned above the 1:1 line showed a pronounced P limitation in the microbial commu- nity (Figure 2A). The relative C and P limitation of microbes was quantified by calculating the vector lengths and angles. Linear- regression analysis revealed no significant correlation between C and P limitation in either the 0–10 cm surface (r2 = 0.01, p = 0.71) or the 20–30 cm subsurface soils (r2 = 0.04, p = 0.40; Figure 2B). Two-way ANOVA revealed that different tree species, soil depth and their interaction had significant effects on vector length and vector angle. Soil depth had a more pronounced effect on enzymatic vector characteristics, followed by tree species and their interaction effects (Table 1). The vector angles of all tree species plantations ranged from 76.17° to 85.36° in surface soils and from 79.91° to 86.47° in subsurface soils, all exceeding 45°, indicating pronounced P limita- tion. Compared with the six native tree species plantations, P limita- tion in Eucalyptus plantations was generally lower, with significant differences particularly compared with R. championii, M. laosensis and M. chapensis in surface soils, whereas no significant differences were observed in subsurface soils (Figure 2C). However, C limitation in Eucalyptus plantations was slightly higher than that of six native tree species plantations, but the difference were not statistically significant in surface soils, except for C. hystrix. Specifically, in subsurface soils, C limitation in Eucalyptus plantations was significantly higher than that in R. championii and M. chapensis plantations, but did not signifi- cantly differ from that in other native tree species plantations (Figure 2D).

  Effects of converting Eucalyptus plantations to six native tree species on microbial nutrient limitation in subtropical plantation soils · 2026 · DOI

• = Microbial metabolic limitation was quantified by calculating vector length and angle of enzymatic activity from untransformed proportional activities, e.g., (BG + CBH)/(BG + CBH + NAG+LAP). The vector length, representing microbial C limitation, was computed Length SQRT(x2 + y2), where x denotes the relative activity of Cas versus P-acquiring enzymes, and y represents the relative activity of C- versus N-acquiring enzymes (Moorhead et al., 2013, 2016). The vector angle, reflecting microbial N or P limitation, was calculated as the arctangent of the line extending from the origin to coordinate ( point (x, y), i.e., DEGREES ATAN x y. Microbial C 2 limitation increases with vector length. Vector angles >45° signify microbial P limitation, and vector angles <45° denote microbial N limitation. As the vector angle increases, microbial P limitation becomes more pronounced, while microbial N limitation diminishes.

  Effects of converting Eucalyptus plantations to six native tree species on microbial nutrient limitation in subtropical plantation soils · 2026 · DOI

• However, this influence is not satisfactorily understood due to contrasting data among literature for the cation exchange capacity (CEC) and the lack of standard analysis methods for CEC of biochar and soil-biochar mixtures.

  Identifying biochar production variables to maximise exchangeable cations and increase nutrient availability in soils · 2024 · DOI

• 5.1. Structure–property–activity relationship for the interactions between organic carbon and minerals Based on the proposed reaction mechanisms, the interaction route between the organic carbon and minerals is highly variable and mainly depends on the structure and characteristics of both minerals and organic carbon. Different interaction routes can lead to contrasting fate of soil carbon. Current studies mainly evaluate this impact by selecting specific natural organic carbon or minerals without a well-designed control on the properties, speciation, and composition. The currently available re- sults are essential for explaining the interaction mechanisms under spe- cific conditions in the soil environment, but they might be less instrumental in evaluating and predicting the potential interactions and long-term stability in a broad spectrum of soils. The impact of SOC composition, abundance of surface functionality, aromaticity, molecular weight distribution, and so on, on the interactions with soil minerals merits a more profound understanding based on the molecular and nano- sized scale design. Furthermore, the speciation, particle size, crystal- linity, and surface properties of the soil minerals will concurrently and significantly affect the interactions with SOC, which needs further exploration in mechanistic studies. 5.2. Variation of organic carbon-mineral interactions and carbon stability with time Many studies evaluated the interaction mechanisms between organic carbon and minerals in the soil environment, but most have only focused on one single snapshot rather than the entire timeline of the interaction process. These studies often span several months or years under relatively stable conditions, which may not always be guaranteed in the natural environment. The interactions between fresh organic carbon and min- erals at the initial stage will change their properties, leading to a different interaction route in later stages. Different alternations of the properties and compositions of SOC and minerals might occur in the second stage, causing distinctive interaction processes afterward. In other words, the primary interactions are variable with dynamic equilibrium, which is related to the changes in the environmental situations (e.g., variation of temperature or precipitation). The full-view findings across different stages can help to explain the past (formation route), the present (current content and existing forms), and the future (predicted transformation and long-term stability) of organic carbon and minerals. 5.3. Spatiotemporal variability of the interactions between organic carbon and minerals Many studies have investigated the interactions between organic carbon and minerals under specified conditions based on the studied soil, while its variation is widely overlooked. In addition to the compositions and properties of the organic carbon and minerals, other variability related to the site locations and weather conditions, e.g., soil pH, tem- perature, water content, co-existing moieties, and redox conditions, can 68 Z. Xu, D.C.W. Tsang Eco-Environment & Health 3 (2024) 59–76 also significantly affect the interaction processes. Linking the cross- linking properties of soils with the potential interactions between organic carbon and minerals can be a fundamental direction for more accurately evaluating soil carbon storage.

  Mineral-mediated stability of organic carbon in soil and relevant interaction mechanisms · 2024 · DOI

• However, the relative importance of two main types of soil minerals ‐ metal oxides and silicate clay—in SOC protection remains unclear, hampering our ability to predict and protect this important pool of persistent SOC.

  Organic Carbon and Lignin Protection by Metal Oxides Versus Silicate Clay: Comparative Study Based on Wetland and Upland Soils · 2023 · DOI

• Abstract Soil respiration—the flow of biologically‐generated CO 2 from the soil surface to the atmosphere—is a major component of global carbon cycling, but the long‐term response of this flux to altered precipitation regimes remains uncertain, due to different responses of soil respiration in distinct ecosystems with varying degrees of water limitation.

  Soil Respiration Response to Simulated Precipitation Change Depends on Ecosystem Type and Study Duration · 2022 · DOI

• n the Northeast Himalayas (NEH) region, four major conventional land-use types are forest, Jhum lands, fallow Jhum lands and plantations, but little is known about their sustainability and responses to changes.

  The impact of traditional land use management on soil quality in Northeastern Himalayas (India) · 2021 · DOI

• However, the relationship between the litter decomposition process and the decomposition stage, precipitation, and litter quality has rarely been addressed, precluding our understanding of how litter decomposition regulates nutrient cycling in various ecosystems and their responses to climate change.

  Mass loss and nutrient release during the decomposition of sixteen types of plant litter with contrasting quality under three precipitation regimes · 2020 · DOI

• Nevertheless, the influence of soil characteristics and climate parameters on microbial extracellular enzyme activity (EEA) performance at different water availabilities and temperatures remains to be detailed.

  Environmental factors affect the response of microbial extracellular enzyme activity in soils when determined as a function of water availability and temperature · 2020 · DOI

• 49‰) showing the same overall C source, 14 C‐ages varied widely from 1,170 ± 20 to 16,200 ± 55 years before present, indicating different deposition‐conditions and subsequent‐processes among the soil samples.

  Yields and Characterization of Dissolved Organic Matter From Different Aged Soils in Northern Alaska · 2018 · DOI

• SRCW was beneficial for the chickens, but the combination needs to be studied further with a focus on strategies for preventing nutrient leaching to groundwater.

  Interactions between broiler chickens, soil parameters and short rotation coppice willow in a free-range system · 2018 · DOI

• The volume of accumulated information on the distribution of micromycetes in soils in Kazakhstan atthe moment remains insufficient, which determines the value of the studies and obtained results aboutthe abundance and distribution of filamentous fungi and yeasts in uncultivated soil and agrocenosis soilsof the agro-industrial firm «Turgen».

  The quantitative composition of the complexes of micromycetes in soils of agrocenoses · 2017 · DOI

• Abstract In contrast to upland croplands, carbon dioxide (CO 2 ) emission from soils has rarely been investigated previously in fields with paddy rice cultivation.

  Seasonal and diurnal variations in net carbon dioxide flux throughout the year from soil in paddy field · 2014 · DOI

• However, we found limited evidence for interactions among elevated CO2, warming, increased precipitation, and enhanced N supply on the other N cycling processes examined: statistically significant interactions, when found, tended not to persist across multiple dates.

  Testing interactive effects of global environmental changes on soil nitrogen cycling · 2011 · DOI

Most-cited papers in Soil Carbon and Nitrogen Dynamics

• Soil organic matter priming: The <scp>pH</scp> effects · Global Change Biology · 2024 · 322 citations
• Role of Soil Microbiota Enzymes in Soil Health and Activity Changes Depending on Climate Change and the Type of Soil Ecosystem · Biology · 2024 · 280 citations
• Nutrient-induced acidification modulates soil biodiversity-function relationships · Nature Communications · 2024 · 222 citations
• Soil Microorganisms: Their Role in Enhancing Crop Nutrition and Health · Diversity · 2024 · 192 citations
• Global turnover of soil mineral-associated and particulate organic carbon · Nature Communications · 2024 · 169 citations
• Shifts in C-degradation genes and microbial metabolic activity with vegetation types affected the surface soil organic carbon pool · Soil Biology and Biochemistry · 2024 · 168 citations
• Biochar and organic fertilizer applications enhance soil functional microbial abundance and agroecosystem multifunctionality · Biochar · 2024 · 167 citations
• Microbially mediated mechanisms underlie soil carbon accrual by conservation agriculture under decade-long warming · Nature Communications · 2024 · 160 citations
• Global analysis of soil bacterial genera and diversity in response to pH · Soil Biology and Biochemistry · 2024 · 147 citations
• A global meta-analysis on the effects of organic and inorganic fertilization on grasslands and croplands · Nature Communications · 2024 · 139 citations

Most recent work

• Comparative effects of digestion residue-derived and corn straw biochar on free-living diazotrophs in nitrogen-deficient calcareous purple soil · Biology and Fertility of Soils · 2026
• Biochar orchestrates coordinated soil-microbe-metabolite responses in acidifying paddy soils: evidence from a 5-year field study · Biochar · 2026
• Effects of Fertilization and Ridge Furrow Planting Patterns on Soil Microbial Communities, Nutrient Dynamics, and Maize Productivity · Biology · 2026
• Differential Ecological Responses of Acidified Greenhouse Soils to Different Amendment Treatments · Agriculture · 2026
• Organic carbon pools and soil health indicators along a decadal mulching chronosequence in a tropical banana system: Implications for land management · Agriculture Ecosystems & Environment · 2026
• Depth-coupling pattern between forest soil microorganisms and carbon mineralization in southwestern China · CATENA · 2026
• Optimizing biochar selection for soil amendment: Unraveling the feedstock-texture interplay for enhanced crop performance · Bioresource Technology · 2026
• Spatiotemporal variation in soil carbon-to-nitrogen and carbon-to-hydrogen ratios: a case study from agricultural farmlands in Southern Texas, USA · Frontiers in Soil Science · 2026
• Effects of converting Eucalyptus plantations to six native tree species on microbial nutrient limitation in subtropical plantation soils · Frontiers in Microbiology · 2026
• Contrasting acidic and alkaline biochar reprogram alfalfa metabolism and rhizosphere microbiomes in saline-alkali soils · Biochar · 2026

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