Optimizing long-term soil organic carbon (SOC) sequestration requires a mechanistic understanding of spatial variability and drivers of stable carbon pools. This study quantified the responses of stable mineral-associated (MAOM) and labile particulate organic matter (POM) to contrasting management systems in a commercial agricultural setting, identified key environmental drivers, and developed predictive spatial models. The study was conducted on Chernozem soils (291 ha) in the Russian forest-steppe ecotone, comparing a conventional tillage (CT) system (sunflower-wheat) with two no-tillage (NT) systems (soybean-sunflower-wheat) established for 5 and 8 years. NT systems received moderate nitrogen inputs (21-34 kg N ha-1 annually), whereas CT received none. Ninety soil samples (0-10 cm) were analyzed using particle-size fractionation, microbial approach, X-ray diffraction and statistical modeling. NT had significantly increased MAOM (22-27 %) while decreasing POM (9-23 %) compared to CT. MAOM increased with MBC and dolomite content, but decreased with quartz content in silt-clay fraction (16 %, 8 % and 11 % of explained variance, respectively), underscoring microbial-mineral stabilization pathways. In contrast, POM variability was poorly predicted by soil microbial and mineral properties. Gradient boosting machine models integrating remote sensing indices with soil properties (SOC, MBC, quartz) achieved high predictive accuracy for both MAOM (R2 = 0.77) and POM (R2 = 0.73), enabling farm-scale mapping of these pools. Our results demonstrate that short-term NT, coupled with soybean inclusion and N fertilization can enhance SOC stability within a relatively short timeframe through microbial mediation. The integration of soil and remote sensing data offers a powerful framework for targeted SOC management and landscape-scale sequestration strategies in temperate agroecosystems, with potential relevance for other regions.

Adapting agriculture to long-term accrual of organic carbon (С) is beneficial both for ensuring food security and for mitigating climate change. This study quantified the responses of total soil C content and its constituent pools to implementing no-tillage (NT) versus conventional tillage (CT) on farms with contrasting water regimes. The farms were chosen at two sites in the Russian steppe zone: Rostov with non-waterlogged Calcic Chernozem (CCH; sunflower-wheat rotation) and Krasnodar with periodic waterlogged Stagnic Chernozem (SCH; maize-wheat rotation). At each site, we surveyed the 0–10 cm and 10–30 cm soil layers in one continuous CT field and two short-term NT fields (8–14 years). The average C content in CCH was higher than in SCH (22.5 vs 17.7 g kg–1). For both sites, NT showed the potential for an increase in C content (by 12–16%) relative to CT only in the 0–10 cm topsoil. Microbial-available C pool (mineralized for 180 days of soil incubation) was most sensitive to tillage systems, unlike unchanged particle-size pools. Specifically, it increased from CT to NT for CCH (by 7–16%), but it showed a decreased trend for SCH (by 11–29%), possibly due to the worsening of soil aeration in the periodically flooded regime. Gradient boosting machine models accurately predicted the spatial distribution of topsoil C content (R2 = 0.99) and its microbial-available pool (R2 = 0.78%) across the farmland area. The mutual drivers of both parameters were topography (elevation) and vegetation distribution (near-infrared surface reflectance). These outcomes are useful for developing site-specific management strategies to effectively restore C stocks in Chernozem soils.

Using the normalized difference vegetation index (NDVI) as a proxy for soil fertility would be highly useful for adapting no-tillage to specific environmental conditions and for monitoring soil quality. Therefore, our study aimed to evaluate the relationship between satellite-based NDVI (May-August 2022) and soil fertility under no-tillage in the forest-steppe of Russia, considering different Chernozems (Haplic and Luvic) and treatments (none / with microbial inoculation and irrigation). Among the soil fertility indices (0–10 cm), content of organic and in organic C (SOC and Cinorg), total N, available P and K, SOC:N, pH, microbial bio mass (MBC) and respiration were assessed. Overall, soil nutrient dependence of NDVI was found for Luvic Chernozem in both microbe-inoculated (SOC, N, K with R2 = 0.72 – 0.95) and untreated sites (SOC, SOC:N with R2 = 0.58 – 0.66). For Haplic Chernozem, only a negative relationship between NDVI and Cinorg was found (R2 = 0.47) at an untreated site, which was eliminated by using irrigation with microbial inoculation. Thus, NDVI can be a robust tool for predicting soil nutrient levels for no-tilled Luvic Chernozem, but not for Haplic Chernozem. At the same time, applied treatments can significantly change the specifics of this relationship, which is important to consider in remote sensing of soil fertility.

The equilibrium between energy persistence and microbial accessibility of soil organic matter (SOM) determines its contribution to climate mitigation and soil health. Labile SOM maintains the activity of soil microorganisms, which provide nutrients for crops and increase yields. Stable SOM is crucial to long-term carbon (C) storage and sequestration in soils. No-till and subsoiling combined with straw return increase SOM content and stocks, yet their specific impacts on the thermodynamic equilibrium between SOM stability and availability remain unclear. We studied the effects of 22 years of no-till and subsoiling with straw return on SOM thermal stability in loamy Calcaric Cambisols. SOM thermal stability was assessed based on the balance between the energy density (ED) in labile, stable, persistent, and refractory SOM and their activation energy (Ea) for thermal oxidation. The energy properties of SOM were evaluated via differential scanning calorimetry and thermogravimetry of soils from six treatments (3 tillage practices (no-till, subsoiling, and conventional tillage as a control) with 2 straw management practices (straw return and straw removal) at 0-12 cm, 12-30 cm and 30-35 cm depths. Compared with conventional tillage, long-term no-till and subsoiling increased the content and thermal stability of SOM, with these effects being amplified by straw return. Conservation tillage with straw return contrastingly affects SOM pools: 1) Ea of labile SOM decreased by 5 %, increasing energy availability for microorganisms; and 2) Ea of recalcitrant SOM increased by 10 %, which was sixfold higher Ea than thermally labile SOM. Subsoiling preferentially raised the content of energy-rich SOM pools, whereas no-till demonstrated superior efficacy in thermodynamic stabilization of SOM compared to subsoiling. Conservation tillage with straw return increased both highly stable organic C and energy-rich available C. Concluding, conservation tillage (no-till and subsoiling) increased content of available energy in soil via contribution to labile SOM, and intensified C stabilization through increased energetic constraints of persistent SOM. This makes conservation tillage with straw return a promizing strategy for climate-smart soil management.

Treelines are advancing upward on mountain slopes due to climate warming and reduced grazing intensity. However, the effects of initial vegetation changes on soil C, N, and P retention, microbial biomass, and catabolic diversity in the subalpine meadows during the early stages of treeline shifts remain poorly understood. This research aimed to better understand the direction and drivers of microbial processes related to C, N, and P cycles in the soil of subalpine natural and grazed meadows, with treatments involving meadow grasses alone (GR, control) and as a mixture with forest litter, specifically birch leaves (BLs), in a one-year microcosm experiment. The addition of BLs with GR resulted in a 12–67% decrease in the retention of C, N, and P in soil microbial biomass, but an 8–9% increase in catabolic diversity compared to the control. The most pronounced effect was observed in the N content of the soil microbial biomass (MBN) for both land uses. The increased proportion of recalcitrant plant residue fractions (acid-insoluble and non-polar extractables) contributed to the decrease in soil MBN content. This shift also reduced the microbial metabolic response to carbohydrates in total substrate-induced respiration, leading to a more balanced and catabolically diverse microbial community. These results improve our understanding of the early response of C, N, and P cycling in mountain soils to treeline shifts mediated by climate warming.

The increasing popularity and recognition of citizen science approaches to monitor soil health have promoted the idea to assess soil microbial decomposition based on a standard litter sample - tea bags. Although tea bag initiatives are expanding across the world, the global datasets remain biased in regard to investigating regions and biomes. This study aimed to expand the tea bag initiative to European Russia, which remains a "white spot" on the tea bag index map. We also added urban soils into the analysis, which were underestimated previously. We compared the standard and local tea brands to explore possible adaptations of the standard approach to regions with limited access to standard tea brands. The established monitoring network included natural and urban sites in six vegetation zones along a 3000 km latitudinal gradient. There was a very close linear relationship (R 2 = 0.94-0.98) in the mass loss of alternative and standard tea litter. The mass loss of green tea in soil along the latitudinal gradient showed an increasing trend from north to south. Variations in the microbial decomposition of green tea were mainly explained by the latitudinal gradient, with low soil temperature identified as key factors hampering decomposition. Mass loss of the more recalcitrant rooibos tea was mainly determined via land use, with decomposition rates on average 1.3 times higher in urban soils. This pattern was in line with higher soil temperatures and pH in urban sites compared to natural counterparts. The findings of our study could prove valuable in extending the tea bag network of soil decomposition assessment into broader territories, including urban areas. Additionally, they could facilitate the involvement of citizen science and complete the database for C cycle modeling depending on climatic conditions.

Climate and land use changes are causing trees line to shift up into mountain meadows. The effect of this vegetation change on the partitioning of soil carbon (C) between the labile particulate organic matter (POM–C) and stable mineral-associated organic matter (MAOM–C) pools is poorly understood. Therefore, we assessed these C pools in a 10 cm topsoil layer along forest–meadow ecotones with different land uses (reserve and pasture) in the Northwest Caucasus of Russia using the size fractionation technique (POM 0.053–2.00 mm, MAOM < 0.053 mm). Potential drivers included the amount of C input from aboveground grass biomass (AGB) and forest litter (litter quantity) and their C/N ratios, aromatic compound content (litter quality), and soil texture. For both land uses, the POM–C pool showed no clear patterns of change along forest–meadow ecotones, while the MAOM–C pool increased steadily from meadow to forest. Regardless of land use, the POM–C/MAOM–C ratio decreased threefold from meadow to forest in line with decreasing grass AGB (R2 = 0.75 and 0.29 for reserve and pasture) and increasing clay content (R2 = 0.63 and 0.36 for reserve and pasture). In pastures, an additional negative relationship was found with respect to plant litter aromaticity (R2 = 0.48). Therefore, shifting the mountain tree line in temperate climates could have a positive effect on conserving soil C stocks by increasing the proportion of stable C pools.

Mountains occupy almost a quarter of the land area and store significant pools of soil organic matter (SOM), which is a potential source of atmospheric CO2 under warming climate. However, carbon fluxes in mountain areas with high environmental heterogeneity remain poorly understood, in particular regarding the spatial variability of soil respiration (RS). The study was conducted on the northeastern slope of the Northwest Caucasus Mountains (1260-2480 m a.s.l.; Russia) that crossed five vegetation belts (i.e., mixed, fir and deciduous forests, subalpine and alpine meadows). RS was measured simultaneously (at 10 a.m. on 11 August 2018) across five vegetation belts (at 12 randomly distributed points per belt; totally n = 60) using the closed static chamber technique. As potential drivers of RS spatial variability, soil physico-chemical (temperature, moisture, total and dissolved C and N contents, C:N ratio, pH), soil microbial (microbial biomass C content, basal respiration, enzymatic activities: β-glucosidase, chitinase and leucine aminopeptidase) and vegetation properties (grasses projective cover, its species richness, Shannon-Wiener diversity index, abundance of graminoids and forbs) were assessed. The RS rate ranged from 1.3-12.7 µmol CO2 m-1 s-1, with average values of 3.7 and 7.3 µmol CO2 m-1 s-1 for forests and grasslands respectively. Stepwise regression and subsequent path analysis showed that key driver of RS spatial variability in forests was temperature-sensitive soil chitinase activity (explained variance 50%), while in grasslands it was graminoid abundance (explained variance 27%). The forest soils are mostly limited in N, therefore RS variability depends largely on SOM-derived CO2 sources, i.e. activity of the N-acquiring enzyme. In the grasslands, extensive network of fine roots and the associated considerable contribution of root-derived respiration to Rs, makes the flux more sensitive to vegetation composition and associated phenology and C allocation patterns. Thus, soil N availability and differences in plant cover play a crucial role in regulation of RS spatial patterns in mountains ecosystems.This study was financially supported by Russian Science Foundation, No 22-74-10124.

In six forest parks of Moscow and four rural forests (5 plots each, n = 50), soil physical, chemical and microbial properties of the upper 10 cm layer were assessed in combination to vegetation properties. The content of carbon (C), nitrogen (N), and phosphorus (P) in soil and microbial biomass was determined. It was revealed that soil density, pH value, content of N–\({\text{NO}}_{3}^{ - },\) Ca and heavy metals (Pb, Cu, Ni, Zn) increase in forest parks compared to rural forests. In the soil of the forest parks, a decrease in the content of microbial biomass C (Cmic), its basal respiration (BR), and microbial C- and N-availability (Cmic/C, Nmic/N, BR/C) was noted. The changes of soil microbial properties are mainly driven by the abundance of leaf litter and the content of available soil C (13–35% of the explained variance). The microbial response to the soil enrichment by low molecular weight organic substrates (carbohydrates, carboxylic and phenolic acids, amino acids, amino sugars) in forest parks and rural forests did not differ significantly. In the soils of forest parks, no changes in microbial mineralization and immobilization of P (Pmic, Pmic/P) were found as well. The impact of urbanization on the forest ecosystems has led mainly to a decrease in the intensity of processes associated with soil C and N cycles. Apparently, such changes are caused by the recreational activity and the management practice of green spaces in the city, which leads, in particular, to a decrease in the amount of forest litter in parks compared to rural forests.

The transition from conventional soil treatment technology to zero treatment technology contributes to an increase in carbon sequestration (Sorg) in the form of carbon dioxide (CO2) from the atmosphere into the soil and, as a result, a reduction in the adverse effects of the greenhouse effect on the ecological state of the environment. The effectiveness of the application of zero tillage is to a greater or lesser extent due to specific agro-climatic conditions, crop rotation systems, fertilizers and plant protection, soil quality and stability. The influence of zero tillage on the dynamics of sorghum reserves and greenhouse gas emissions (CO2, N2O, CH4) in the agro-climatic conditions of crop production (LLC “Orlovka AIC”, Samara region) was investigated. The study was conducted on agrochernozem heavy loam in September–November 2021 in conditions of an abnormally arid growing season and high summer temperatures. On plots with zero tillage, plant residues were received: 268–1720 kg С/ha, 3–66 kg N, 0.2–7.7 kg P and 12–44 kg K/ha. Based on the results obtained, recommendations are proposed for further improving the efficiency of zero tillage technology due, firstly, to reducing its adverse effect on the density of soil composition, and, secondly, taking into account the influence of underlying parent rocks and relief on water erosion of soil and redistribution of granulometric fractions of soil in the agricultural landscape, which will allow using this technology according to principles of adaptive landscape farming.

Canola cultivation at high latitudes is becoming more promising in terms of modern climate change. Sustainable crop production requires an understanding of yield-limiting factors, which need to be adjusted in agricultural management first. Therefore, our study was aimed at examining the effect of climate and soil fertility factors on the canola yield from 2012 to 2015 in northwestern Russia. Simultaneously, effectiveness of chemical fertilizer (N65P50K50 and N100P75K75) rates was tested. Studied soils had light texture, high acidity and severe sulfur deficiency. Canola yield (Y) varied from 0.81 to 1.60 t·ha−1 for the observed period. Applied fertilizer increased Y by around 30%, but this change was not significant. Climate effect testing with the FAO-AquaCrop simulation showed no noticeable water and heat stresses for the study period (0% to 20% reduction in potential Y). Among the tested soil properties, the content of organic carbon, available nitrogen and sulfur significantly correlated with Y (r = 0.58–0.66). Combining these factors together with soil pH in a path model explained 60% of variability in Y. Importantly, sulfur had the highest and most significant effect in this model. Thus, this soil parameter is the main yield-limiting factor in the study area, which must be the first to be adjusted in agricultural practice.

The patterns of change in bioclimatic conditions determine the vegetation cover and soil properties along the altitudinal gradient. Together, these factors control the spatial variability of soil respiration (R-S) in mountainous areas. The underlying mechanisms, which are poorly understood, shape the resulting surface CO2 flux in these ecosystems. We aimed to investigate the spatial variability of R-S and its drivers on the northeastern slope of the Northwest Caucasus Mountains, Russia (1,260-2,480 m a.s.l.), in mixed, fir, and deciduous forests, as well as subalpine and alpine meadows. R-S was measured simultaneously in each ecosystem at 12 randomly distributed points using the closed static chamber technique. After the measurements, topsoil samples (0-10 cm) were collected under each chamber (n = 60). Several soil physicochemical, microbial, and vegetation indices were assessed as potential drivers of R-S. We tested two hypotheses: (i) the spatial variability of R-S is higher in forests than in grasslands; and (ii) the spatial variability of R-S in forests is mainly due to soil microbial activity, whereas in grasslands, it is mainly due to vegetation characteristics. Unexpectedly, R-S variability was lower in forests than in grasslands, ranging from 1.3-6.5 versus 3.4-12.7 & mu;mol CO2 m(-1) s(-1), respectively. Spatial variability of R-S in forests was related to microbial functioning through chitinase activity (50% explained variance), whereas in grasslands it was related to vegetation structure, namely graminoid abundance (27% explained variance). Apparently, the chitinase dependence of R-S variability in forests may be related to soil N limitation. This was confirmed by low N content and high C:N ratio compared to grassland soils. The greater sensitivity of grassland R-S to vegetation structure may be related to the essential root C allocation for some grasses. Thus, the first hypothesis concerning the higher spatial variability of R-S in forests than in grasslands was not confirmed, whereas the second hypothesis concerning the crucial role of soil microorganisms in forests and vegetation in grasslands as drivers of R-S spatial variability was confirmed.

The introduction of resource-saving technologies into the practice of agriculture is one of the approaches to preserving soil fertility and increasing the reserves of organic carbon (Сorg). One of such technologies is zero tillage, which has been actively used all over the world since the middle of the twentieth century. However, there is still insufficient information about the effectiveness of this technology for the accumulation and preservation of Сorg in the agro-soils of our country. The paper estimates the rate of accumulation of Сorg by agrochernozems with zero tillage in the conditions of the Middle Volga region. On the territory of agricultural farms (Pokhvistnevsky district of the Samara region), 2 agricultural fields with 5- and 8-year zero tillage (88 and 161 hа, respectively) and a field with non-fallow plowing (42 hа) were selected. 30 study points were selected in each field, from which soil samples of the upper (0–10 cm) and lower (10–30 cm) layers of humus-accumulative and partially illuvial horizons were selected. The paper presents the main physic-chemical parameters of the soil and calculated the reserves of Сorg. A significant increase in sorghum reserves in the upper soil layer was shown at 5- and 8-year zero tillage (on average by 0.57 and 0.45 kg/m2) compared with those during plowing, but no significant differences were found for the lower layer. The total sorghum reserves for the 0–30 cm soil layer at zero tillage increased by 0.61 and 0.34 kg/m2 relative to those during plowing. Consequently, as a result of the application of zero processing, the rate of accumulation of Сorg reserves in the agrochernozems of the Middle Volga region can reach 1.22 and 0.43 t/ha per year, which is 1.3–41 times more than the recommended program “4 ppm” for agricultural lands of our country (from 0.03 to 0.33 t/ha per year).

Abstract Application of different types of feedstocks and conditions of their pyrolysis can result in different properties and sustainability of biochar during changes (aging) of its properties in soils. The aim of the studies was to assess the consequences of aging of biochar in soil for a content of adsorbed film water and a density of oxygen-containing functional groups on its surface. Sampling of soil and biochar was conducted in May and July of 2021 in a plot experiment with an applied rate of biochar of 20 t.ha−1 in 2016. WP4-T dew point potentiometer was used for measurements of relationships of potentials of adsorbed film water and its content in soil and biochar. Infrared Fourier FSM 2201/2202 spectrometer was applied for determination of densities of oxygen-containing functional groups on surface of biochar in a mid-infrared spectrum. Results showed that retention capacity of adsorbed film water by soil increased from May to July, possibly because of increasing content of hydrophilic organic compounds of plant origin. Aging of biochar in soil also resulted in an increase of retention capacity of adsorbed film water on its surface. The results of infrared Fourier spectroscopy confirmed that densities of oxygen-containing functional groups on the surface of biochar increased from May to July at spectra of wavenumbers of 1,600–1,400 cm−1 and 1,400–1,100 cm−1.

Rising air temperatures caused by global warming affects microbial decomposition rate of soil organic matter (SOM). The temperature sensitivity of SOM decomposition (Q10) may depend on SOM quality determined by vegetation type. In this study, we selected a long transect (3.6 km) across the five ecosystems and short transects (0.1 km) from grazed and ungrazed meadows to forests in the Northwest Caucasus to consider different patterns in Q10 changes at shift of the vegetation belts. It is hypothesized that Q10 will increase along altitudinal gradient in line with recalcitrance of SOM according to kinetics-based theory. The indicators of SOM quality (BR:C, respiration per unit of soil C; MBC:C, ratio of microbial biomass carbon to soil carbon; soil C:N ratio) were used for checking the hypothesis. It was shown that Q10 did not differ across vegetation types within long and short transects, regardless differences in projective cover (14–99%) and vegetation species richness (6–12 units per plot). However, Q10 value differed between the long and short transects by almost two times (on average 2.4 vs. 1.4). Such a difference was explained by environmental characteristics linked with terrain position (slope steepness, microclimate, and land forms). The Q10 changes across studied slopes were driven by BR:C for meadows (R2 = 0.64; negative relationship) and pH value for forests (R2 = 0.80; positive relationship). Thus, proxy of SOM quality explained Q10 variability only across mountain meadows, whereas for forests, soil acidity was the main driver of microbial activity.

An altitudinal gradient in the mountains constitutes a unique 'open-lab' to examine environmental hypotheses and analyse the expected effects of global warming. The distribution of carbon (C)-, nitrogen (N)-, and phosphorus (P)-acquiring enzyme activity, microbial catabolic activity as represented by a community-level physiological profile (CLPP), and microbial functional diversity (HCLPP) within mountainous ecosystems consisting of mixed, fir and deciduous forests, as well as subalpine and alpine meadows (1260-2480 m a.s.l., Mt. Tkachiha, the Northwest Caucasus, Russia) has been studied. Concerning potential drivers, vegetation (plant projective cover, plant functional group composition, plant richness and diversity) and edaphic (soil nutrients: total and available C and N, total P, pH, texture, temperature, microbial biomass C) and topographic (elevation, slope, mean annual temperature calculated using biannual monitoring data) properties have been considered. The distribution patterns of the studied hydrolytic enzymes along an altitudinal gradient cannot be explained solely by elevation change and soil nutrient content. The activity of soil leucine aminopeptidase depends on vegetation type and graminoid abundance. beta-D-glucosidase activity was mainly driven by the quality of soil organic matter (SOM), demonstrating a significant relation with the soil C:N ratio. The chitinase and phosphatase turned out soil temperature-sensitive enzymes. The CLPP depends on the available N content in the soil. The HCLPP distribution with altitude was driven by available N and forbs abundance represented by the widest spectrum of plant families and species. An altitudinal gradient determines the spread of the vegetation zone. In turn, vegetation properties, such as plant functional group composition, species richness and diversity, play a significant role in the distribution of soil microbial activity along an altitudinal gradient that controls the decomposition of SOM and nutrient cycling. Thus, the significant role of vegetation in the distribution of soil microbial activity across a wide range of natural ecosystems and in consideration of topographic and edaphic factors has been demonstrated.

In mountain areas, one of the noticeable results of modern climate change is rapid shift of treelines to subalpine and alpine meadows. Such vegetation shifts is associated with a change in quality of the plant residues entering the soils, which in turn can affect the mineralization activity (basal respiration) and functional diversity of the soil microbial community. Therefore, the study was aimed at assessing the soil microbial (basal respiration and functional diversity) and chemical (C, N, C/N, pH) properties (0-10 cm) along the reserved and grazed forest-meadow transects of the Northwestern Caucasus (Karachay-Cherkess Republic), as well as evaluating an effect of vegetation type and land use on variation of these soil properties. It was found that the C and N contents (for both land usees), pH and basal respiration (reserved slope) significantly increase from forest to meadow soils. In contrary, the microbial functional diversity decreased from forest to meadow soils, which might be due to less diverse organic compounds entering the soil only with grass residues than their combination with forest litter. Two-way ANOVA showed that soil microbial functional diversity, pH, C and N along the studied forest-meadow transects was mostly associated with vegetation type (1439 % of the explained variation), and C/N and basal respiration - with land use (3336 % of the explained variation). Thus, a land use change will have a more significant effect on the mineralization activity of soil microbial community than a treeline shifts.