Soil Carbon Mineralization Research Articles

Effects of Agricultural Land Use on Desert Soil Classification in Holy Karbala Governorate

This study was conducted to evaluate physical, chemical, and morphological features to classify soils at the subgroup level. The research area, located west of Karbala, consists of three locations, each comprising pedons in both cultivated and uncultivated lands. GPS coordinates were recorded, and morphological descriptions of pedon horizons were made in accordance with the American Soil Survey Manual. This study investigates the effect of agricultural land use on the classification of desert soils in the Holy Karbala Governorate. The results revealed that the dry climate caused diversity in the morphological features of the soils, mainly in horizon type, thickness, and arrangement. Agricultural usage had an impact on diagnostic horizons, particularly the gypsic horizon, and features such as soil color, structure, organic matter, carbonate minerals, gypsum, and root distribution. However, there was no substantial impact on soil texture development, and soils did not show a consistent pattern of soil separation distribution with depth, indicating weak pedogenic processes. The most common texture classes were loamy sand, sandy loam, and sand, with sand contents ranged from 902.08 to 574.12 g kg. Soil bulk density differed from 1.67 to 1.30 Mg m³, with lower values in farmed areas. Chemical properties were influenced, with soil pH ranging from 8.36 to 7.54, electrical conductivity (EC) from 5.46 to 2.03 dS m, cation exchange capacity (CEC) from 15.25 to 2.05 meq.100g, organic matter from 43.51 to 1.18 g kg, carbonate minerals from 461.18 to 174.06 g kg, and calcium sulfate from 182 to 21 g kg. The soils were classed as Aridisols because they were found in a dry desert with an Aridic moisture regime. The presence of distinctive saline layers such as Calcic and Gypsic was discovered, resulting in the classification of cultivated soils as Typic Haplocalcids and uncultivated lands as Typic Calcigypsids.

Natural grassland restoration exhibits enhanced carbon sequestration and soil improvement potential in northern sandy grasslands of China: An empirical study

Vegetation restoration is an effective measure for restoring degraded ecosystems. Soil carbon mineralization, a crucial indicator for evaluating the effectiveness of vegetation restoration, is essential in soil carbon cycling. However, the response of soil carbon mineralization to different vegetation restoration types remains unclear. In this study, grassland (Leymus chinensis and Stipa bungeana), shrubland (Corethrodendron fruticosum), and forestland (Ulmus pumila) with 20 years of consistent restoration in the Xilingol sandy grassland were selected to determine the effects of vegetation restoration types on soil carbon mineralization. The results showed that the soil cumulative carbon dioxide emissions (CCE) and microbial respiration rate (SMR) in grassland and forestland were significantly higher than those in shrubland, while soil carbon mineralization efficiency (CME) and microbial metabolic quotient (MQ) were significantly lower than those in shrubland. Furthermore, soil organic carbon (SOC) and its fractions were influenced considerably by vegetation restoration types, with grassland exhibiting the highest SOC content. The ratios of soil total effective nutrients (C/N, N/P, and C/P) and the content of active organic carbon (DOC, MBC, EOC, and POC) can effectively reflect the changes in soil carbon mineralization and the stability of SOC pools. The variations in CCE were influenced by litter biomass, macroaggregates organic carbon, mineral-associated organic carbon (MAOC), and dissolved organic carbon (DOC), while the changes in SMR were affected by aboveground biomass (AGB), soil total nitrogen and phosphorus ratios (N/P), and microaggregate organic carbon and microbial biomass carbon. The changes in CME were affected by AGB, N/P, pH, MAOC, and DOC, while the changes in MQ were influenced by AGB, N/P, DOC, MAOC, and easily oxidizable organic carbon. Given the higher carbon sequestration benefits and soil quality improvement capability of naturally restored grassland, this study suggests that grassland could be considered the primary vegetation restoration type in the Xilingol sandy grassland.

Iron‑carbon complex types and bonding forms jointly control organic carbon mineralization in paddy soils

The crucial role of iron (Fe) oxides in stabilizing soil organic carbon (SOC) is well recognized, but their effects on SOC mineralization remain poorly understood. To address this knowledge gap, we evaluated the effects of four typical Fe-bound OC (Fe-OC) complexes including adsorbed ferrihydrite (Fh)- and goethite (Goe)- 13C, coprecipitated Fh/Goe-13C and 13C-glucose as the control, on OC mineralization during an 80-day anaerobic incubation in a paddy soil. 13C-tracing indicated that Fe-13C complexes significantly stimulated CO2 emissions from both the input 13C and SOC compared with glucose alone. In contrast, the addition of Fh- and Goe-C complexes consistently inhibited CH4 emissions by 72–91 % and 21–61 % compared with glucose addition, respectively. Fe-OC complexes reduced the CO2 equivalent by 62–71 % and 17–41 % in soils with Fh-C and Goe-C complexes, respectively. We concluded that Fe crystallinity and its bonding forms with organic carbon jointly control SOC mineralization. The coprecipitated Goe-C complexes had the lowest OC mineralization rate and highest OC residence time among four Fe-OC complexes. These findings highlighted that promoting the formation of coprecipitated well-ordered minerals would increase SOC sequestration by reducing OC mineralization and mitigating the global warming effect in paddy management.

Soil carbon mineralization decreased in desert steppe by light grazing but not fencing management

Fencing off grassland soils emits massive amounts of carbon into the atmosphere. Whether grazing management in desert steppes with fragile ecosystems can mitigate this trend remains highly uncertain. Here, we examined how soil carbon mineralization, as well as its underlying mechanisms, varied with grazing intensity by sheep in a long-term (17 − year) experiment in the desert steppe. Carbon mineralization decreased by 15 % − 55 % under different grazing intensities compared to fencing controls. Soil organic carbon (SOC) maintained high levels under light grazing, whereas it decreased with increasing grazing intensity. Reductions in plant carbon and absolute microbial abundance due to grazing, coupled with changes in soil carbon quality and the environment, drove the reduction in carbon mineralization. We suggest that mechanisms of carbon mineralization can be integrated into predictive modelling efforts to better understand the impact of grazing on carbon fluxes in ecologically fragile, but globally important, arid and semi-arid grasslands.

The effect of redox fluctuation on carbon mineralization in riparian soil: An analysis of the hotspot zone of reactive oxygen species production

Riparian zones are important depositional environments at the catchment scale and provide environmental services such as carbon sequestration. This zone is a highly dynamic interface for oxygen and electron exchange, which confers the basis for reactive oxygen species (ROS) production. However, the differences in soil ROS production and their impact on carbon turnover across various redox locations within the riparian zone remain to be fully elucidated. In this study, we investigated the distribution characteristics and generation mechanism of ROS in riparian soil based on soil samples collected in a three-month field monitoring experiment, with additional incubation experiments conducted to examine the effect of hydroxyl radical (•OH) on soil organic carbon (SOC) mineralization. The obtained results demonstrated that the riverine wetland was the hotspot zone for •OH production, with the production flux of 13.05 μmol kg−1 d−1, which was significantly higher than that in floodplain (7.29 μmol kg−1 d−1) and riverbank soils (8.61 μmol kg−1 d−1). Moreover, •OH levels displayed distinct rhythmic fluctuations, with significantly higher concentrations at low water levels compared to those at high water levels, and remained essentially flat over three cycles. The statistic analysis revealed that the ROS production was highly dependent on reduced species and microbial community structure, which function as biogeochemical batteries and electron shuttles under redox fluctuations. Furthermore, the generated •OH involved in the abiotic mineralization of SOC, contributing to 13.1‒21.8 % of total CO2 efflux. Compared to particulate organic carbon (POC), mineral-associated organic carbon (MAOC) fractions of SOC were more susceptible to •OH attacks. The findings provide a novel insight to comprehensively assess the redox process on riparian carbon turnover.

Forest soil carbon storage in 10‐year‐old Douglas‐fir plantations of western Oregon and Washington remains similar to pre‐harvest

AbstractForests around the world, and in the case of this study, the coastal Pacific Northwest United States, store large amounts of carbon, both above ground in the trees and below ground in soils. Understanding the effects of forest disturbance, including timber harvesting, is important in order to evaluate the role that forestry plays in the global carbon cycle. Soil carbon can be difficult to assess with enough precision to detect the kinds of changes that are expected, yet a series of small changes over time in the same direction could have important cumulative effects. In this study, eight randomly selected Douglas‐fir forest stands in Oregon and Washington were sampled at 300 points each using a fixed‐depth sampling approach to attempt to detect a 5% or higher change in soil carbon storage to 1 m, longitudinally from pre‐harvest to 10 years post‐harvest. There was moderate variability in results over time at individual sites, with some sites decreasing slightly and others increasing slightly. Only two sites achieved lower than the 5% minimum detectible difference target. The remaining six sites were able to detect 5.7%–10.7% differences. In one case, an unexpectedly large increase in mineral soil carbon 10 years post‐harvest occurred without clear explanation. On average, forest floor carbon stores were 20% larger 10 years post‐harvest than pre‐harvest. Even with the large increases excluded, both the fixed‐depth approach and equivalent soil mass correction showed there was no significant change in mineral soil carbon stores to 1 m at 10 years post‐harvest in the region.

Pore connectivity and anisotropy affect carbon mineralization via extracellular enzymes in > 2 mm aggregates under conservation tillage of Mollisols

Soil aggregates, which are the basic units of soil structure, play an important role in the carbon cycle of ecosystems. The pore characteristics of aggregates influence soil organic carbon sequestration. However, studies on SOC mechanisms in aggregates have been limited to Mollisols. This study was conducted as a long-term experiment established in 2004 with a corn-soybean rotation in Mollisols. There are three treatments, including rotary tillage without straw return (conventional tillage, CT), subsoiling without straw return (reduced tillage, RT), and no tillage with straw return (NT). The soil pore size distribution, shape parameters, extracellular enzymes activity, and carbon mineralization were measured. The results showed that 15-year no tillage and reduced tillage increased the total porosity and proportion of larger pores, but significantly decreased the proportion of smaller pores in situ soil columns. Conventional tillage exhibited the most complex pores because of the highest pore fractal dimension (2.75–2.90), anisotropy (0.366–0.516), and the lowest sphericity (5.1–28.7). As for the soil columns filled with > 2 mm aggregates, reduced tillage significantly increased the pore connectivity by 3.02–3.62 %, whereas no tillage had no effect. The structural equation modelling indicated that in soil columns filled with > 2 mm aggregates, pore shape parameters, particularly connectivity and anisotropy, positively influenced the activities of β-glucosidase and β-xylosidase directly, and positively affected soil carbon mineralization by influencing extracellular enzymes activity indirectly. The findings emphasize the importance of pore shape parameters effect on soil carbon sequestration, and will be helpful in comprehending the microscopic mechanisms of soil carbon sequestration in > 2 mm aggregates.

The response of soil carbon mineralization losses to changes in rainfall frequency is seasonally dependent in an estuarine saltmarsh

Altered rainfall distribution patterns resulting from climate change have substantial effects on soil carbon (C) cycling in terrestrial ecosystems particularly in water-limited regions. However, how rainfall redistribution affects soil C mineralization (CO2 and CH4 fluxes) in humid regions such as of the coastal saltmarshes remain unclear. We conducted mesocosm experiments in an estuarine saltmarsh in the Yellow River Delta of China, where we simulated three rainfall frequency scenarios (high-frequency, medium-frequency and low-frequency) with the same total rainfall amount in the dry and wet seasons, respectively. Soil CO2 and CH4 fluxes were measured before and after rain frequency treatment during a 40-day period for each season. The decrease in rainfall frequency significantly reduced the mean soil CO2 and CH4 fluxes during the dry season, but had no effect on either flux during the wet season. The seasonal variation in the response of soil C mineralization to rainfall frequency changes could be explained by the changes in antecedent soil water and salinity conditions, soil C substrate, microbial activities and diversity. Thus, the effects of changes in rainfall frequency on soil C mineralization are regulated by season, and should be considered when predicting the future C balance of coastal wetland ecosystems. Furthermore, the shift in precipitation frequency distribution towards increasing heavy rainfall events during the dry season in this region will have a great effect on soil C losses, potentially feeding back into the soil C budget and stability in this estuarine saltmarsh.

Soil fungal and bacterial communities reflect differently tundra vegetation state transitions and soil physico-chemical properties.

Strong disturbances may induce ecosystem transitions into new alternative states that sustain through plant-soil interactions, such as the transition of dwarf shrub-dominated into graminoid-dominated vegetation by herbivory in tundra. Little evidence exists on soil microbial communities in alternative states, and along the slow process of ecosystem return into the predisturbance state. We analysed vegetation, soil microbial communities and activities as well as soil physico-chemical properties in historical reindeer enclosures in northernmost Finland in the following plot types: control heaths in the surrounding tundra; graminoid-dominated; 'shifting'; and recovered dwarf shrub-dominated vegetation inside enclosures. Soil fungal communities followed changes in vegetation, whereas bacterial communities were more affected by soil physico-chemical properties. Graminoid plots were characterized by moulds, pathotrophs and dark septate endophytes. Ericoid mycorrhizal and saprotrophic fungi were typical for control and recovered plots. Soil microbial communities inside the enclosures showed historical contingency, as their spatial variation was high in recovered plots despite the vegetation being more homogeneous. Self-maintaining feedback loops between plant functional types, soil microbial communities, and carbon and nutrient mineralization act effectively to stabilize alternative vegetation states, but once predisturbance vegetation reestablishes itself, soil microbial communities and physico-chemical properties return back towards their predisturbance state.

Stand development reduces soil carbon mineralization in rubber plantations through regulating microbial metabolic strategy and substrate availability

Forest age, a critical variable for land-use decision makers, is known to change soil microbial communities. However, how such changes affect microbial metabolic strategy and the associated soil C mineralization processes in different forest ages remains unknown, especially in tropical region. To address this issue, three different aged rubber plantations, namely 4-year-old (Young, YRP), 15-year-old (Mature, MRP), and 31-year-old (Old, ORP), were studied to reveal the soil mineralization characteristics. Furthermore, to understand the mechanism from the coupled perspective of decomposers and substrate availability, the microbial metabolic strategy was deciphered by 2D-COS-Biolog assay, and linked with soil microbial composition and labile-/recalcitrant- organic pools. Results showed that YRP was characterized by having more copiotrophic taxa (e.g., actinobacteria) and the largest G(-)/G(+) ratio and invertase activity. Thus, YRP exhibited a preferential utilization for carbohydrate and the largest SOC mineralization rate. In contrast, regardless of abundant labile C and N pools in MRP, the soil microbial communities were shifted to oligotrophic taxa in utilizing resistant polymer, and MRP contained abundant G(+), fungi and arbuscular mycorrhizal fungi related to aggregate formation. As a result, the soil mineralization rate in MRP was reduced by 66 % compared with YRP. However, the SOC mineralization rate was unchanged from MRP to ORP, primarily because the increased proportion of recalcitrant nutrient pool, and soil microorganism had greater priority in utilizing relatively resistant amine. The structural equation modeling revealed that the variations in mineralization were mainly regulated by soil microbial composition and metabolic strategy, and partially affected by soil C and N pools. Furthermore, random forest model indicated that soil pH, NH4-N and C/N were also the crucial factor for mineralization by affecting soil microbial communities during stand development. In summary, these findings improve our understanding in soil C budget and contribute to the C accurate management during plantation development.

Maize straw increases while its biochar decreases native organic carbon mineralization in a subtropical forest soil

Organic soil amendments have been widely adopted to enhance soil organic carbon (SOC) stocks in agroforestry ecosystems. However, the contrasting impacts of pyrogenic and fresh organic matter on native SOC mineralization and the underlying mechanisms mediating those processes remain poorly understood. Here, an 80-day experiment was conducted to compare the effects of maize straw and its derived biochar on native SOC mineralization within a Moso bamboo (Phyllostachys edulis) forest soil. The quantity and quality of SOC, the expression of microbial functional genes concerning soil C cycling, and the activity of associated enzymes were determined. Maize straw enhanced while its biochar decreased the emissions of native SOC-derived CO2. The addition of maize straw (cf. control) enhanced the O-alkyl C proportion, activities of β-glucosidase (BG), cellobiohydrolase (CBH) and dehydrogenase (DH), and abundances of GH48 and cbhI genes, while lowered aromatic C proportion, RubisCO enzyme activity, and cbbL abundance; the application of biochar induced the opposite effects. In all treatments, the cumulative native SOC-derived CO2 efflux increased with enhanced O-alkyl C proportion, activities of BG, CBH, and DH, and abundances of GH48 and cbhI genes, and with decreases in aromatic C, RubisCO enzyme activity and cbbL gene abundance. The enhanced emissions of native SOC-derived CO2 by the maize straw were associated with a higher O-alkyl C proportion, activities of BG and CBH, and abundance of GH48 and cbhI genes, as well as a lower aromatic C proportion and cbbL gene abundance, while biochar induced the opposite effects. We concluded that maize straw induced positive priming, while its biochar induced negative priming within a subtropical forest soil, due to the contrasting microbial responses resulted from changes in SOC speciation and compositions. Our findings highlight that biochar application is an effective approach for enhancing soil C stocks in subtropical forests.

Effects of Winery Wastewater to Soils on Mineral Properties and Soil Carbon

Winery wastewater (WW) is a high-volume biowaste and, in the context of Marlborough and New Zealand wineries, there is a growing recognition of the need to improve current WW disposal systems to mitigate negative environmental impacts. The application of WW to land is a low-cost method of disposal, that could significantly reduce the environmental risk associated with WW directly entering surface and groundwater bodies. This study analysed elemental concentrations in WW and soils from three Marlborough vineyards across their annual vintage to determine the loading rates of nutrients into WW and the subsequent accumulation effects of WW irrigation on receiving soils. The findings showed loading rates of approximately 1.8 t ha−1 yr−1 of sodium within WW and a significant increase in soil sodium concentration and pH, attributed to sodium-based cleaning products. A loading rate of approximately 4 t ha−1 yr−1 of total organic carbon was also identified within WW, however, significant losses in soil carbon, nitrogen, magnesium and calcium concentrations were identified. Focusing efforts to retain key nutrients from WW within soils could provide benefits to New Zealand’s wine industry, facilitating increased biomass production in irrigation plots, thereby increasing biodiversity and potentially generating incentives for vineyard owners to contribute to increasing biomass carbon stocks and offset agricultural greenhouse gas emissions.

Aggregate stability and carbon and N dymamics in macroaggregate size fractions with different soil texture

Soil nutrient cycling, the distribution of soil aggregates, and their stability are directly influenced by soil texture. Different sizes of soil aggregates provide microhabitats for microorganisms and therefore influence soil carbon (C) and nitrogen (N) mineralization. The purpose of the present study was to assess the aggregate stability and dynamics of carbon and nitrogen in macroaggregate size fractions (1-8 mm) with different clay content from meadow soils. Surface soil samples (0-15 cm) were collected from 4- to 5-year-old forage crops. Four macroaggregate size classes were isolated by dry sieving and analyzed for their mass proportions: fine macroaggregates (FM) (less than 1 mm), medium-fine macroaggregates (MFM) (1-2 mm), medium-coarse macroaggregates (MCM) (2-4 mm), and large-coarse macroaggregates (LCM) (4-8 mm). The dry mean weight diameter (MWD), organic carbon (OC), total nitrogen (TN), carbon and nitrogen of microbial biomass (C-MB, N-MB) were determined. CO2 emission and net nitrogen mineralized (NM) were measured after 14 weeks of incubation. The amounts of FM were significantly lower than those of intermediate macroaggregates (MCM and MFM) and decreased markedly with increasing clay content within soil macroaggregates. In general, the amounts of macroaggregate size fractions were lowest in soils with high clay content. MWD exhibited a significant correlation with particle size distribution, OC, and MB-C. OC, TN, MB-C, and MB-N contents within macroaggregates increased with decreasing macroaggregate size and increasing clay content of macroaggregate fractions. The CO2 emission and NM content increased with increasing macroaggregate size, indicating higher organic C and N mineralization activity in larger macroaggregates. Mineralization of OC was lowest in macroaggregate fractions with the highest clay content. We conclude that clay content can increase the protection of microbial biomass in meadow soils. Small macroaggregates tend to contain more recalcitrant organic matter compared to larger macroaggregates.

Multi-scale analysis of carbon mineralization in lime-treated soils considering soil mineralogy

Mineral carbonation is emerging as a reliable CO2 capture technology that can mitigate climate change. In lime-treated clayey soils, mineral carbonation occurs through the carbonation of free lime and cementitious products derived from pozzolanic reactions. The kinetics of the reactions in lime-treated clayey soils are variable and depend primarily on soil mineralogy. The present study demonstrates the role of soil mineralogy in CO2 capture and the subsequent changes caused by carbon mineralization in terms of the unconfined compressive strength (UCS) of lime-treated soils during their service life. Three clayey soils (kaolin, bentonite, and silty clay) with different mineralogical characteristics were treated with 4% lime content, and the samples were cured in a controlled environment for 7 d, 90 d, 180 d, and 365 d. After the specified curing periods, the samples were exposed to CO2 in a carbonation cell for 7 d. The non-carbonated samples purged with N2 gas were used as a benchmark to compare the mechanical, chemical-mineralogical, and microstructure changes caused by carbonation reactions. Experimental investigations indicated that exposure to CO2 resulted in an average increase of 10% in the UCS of lime-treated bentonite, whereas the strength of lime-treated kaolin and silty clay was reduced by an average of 35%. The chemical and microstructural analyses revealed that the precipitated carbonates effectively filled the macropores of the treated bentonite, compared to the inadequate cementation caused by pozzolanic reactions, resulting in strength enhancement. In contrast, strength loss in lime-treated kaolin and silty clay was attributed to the carbonation of cementitious phases and partly to the tensile stress induced by carbonate precipitation. In terms of carbon mineralization prospects, lime-treated kaolin exhibited maximum carbonation due to the higher availability of unreacted lime. The results suggest that, in addition to the increase in compressive strength, adequate calcium-bearing phases and macropores determine the efficiency of carbon mineralization in lime-treated clayey soils.

Maize Straw and Nitrogen Fertilizer Alter Soil Carbon and Nitrogen Mineralization during the Fallow Period in the Oasis Farmland area

Maize Straw and Nitrogen Fertilizer Alter Soil Carbon and Nitrogen Mineralization during the Fallow Period in the Oasis Farmland area

Mineralization of microalgal carbon and nitrogen in sodic soils

Mineralization of microalgal carbon and nitrogen in sodic soils

Effects of freeze–thaw cycles on soil nutrients by soft rock and sand remodeling

Abstract To explore the mechanism of freeze–thaw cycles on the nutrient release of soft rock and sand-remodeled soils in Mu Us Sandy land of China, and to clarify the adaptation potential of remodeled soils with different proportions to extreme environment, indoor freezer simulation freeze–thaw experiments were carried out. The research results show that during the 2 cycles of freeze–thaw, the remodeled soil organic matter content and total nitrogen content (TNC) of the three treatments reached their peaks. Compared with that before freezing, T1, T2, and T3 treatments increased TNC by 40.9, 90.2, and 118.9%. The freeze–thaw cycle has a significant impact on the emergence rate of maize (P < 0.05). In the soil during the 2 freeze–thaw cycles, the seedling emergence rate of maize is the highest. Compared with non-freeze–thaw treatment, the maize emergence rate of T1, T2, and T3 treatments was increased by 2, 3, and 3 times, and the emergence rate of T2 and T3 treatments was higher than that of T1 treatments under different freeze–thaw cycles. In conclusion, short-term freeze–thaw cycles can promote soil carbon and nitrogen mineralization and improve nutrient availability in Mu Us Sandy land, and T2 and T3 treatments have better adaptability to the environment.

Effects of Land-Use Type and Salinity on Soil Carbon Mineralization in Coastal Areas of Northern Jiangsu Province

Sea level rise due to glacier melting caused by climate warming is a major global challenge, but the mechanism of the effect of salinity on soil carbon (C) mineralization in different land types is not clear. The pathways by which salinity indirectly affects soil carbon mineralization rates need to be investigated. Whether or not the response mode is consistent among different land-use types, as well as the intrinsic links and interactions between soil microbial resource limitation, environmental stress, microbial extracellular enzyme activity, and soil carbon mineralization, remain to be demonstrated. In this paper, three typical land-use types (wetland, forest, and agroforestry) were selected, and different salinity levels (0‰, 3‰, 6‰, and 32‰) were designed to conduct a 125-day laboratory incubation experiment to determine the soil CO2 release rate, soil physicochemical properties, and soil enzyme activities, and to correlate C mineralization with biotic and abiotic factors. A correlation analysis of soil physical and chemical properties, extracellular enzyme activities, and carbon mineralization rates was conducted to investigate their intrinsic linkages, and a multiple linear regression of C mineralization at different sites was performed to explore the variability of mineralization among different site types. Structural equation models were established in the pre- and post-incubation stages to study the pathways of soil C mineralization at different incubation times, and the mechanism of mineralization was further verified by enzyme stoichiometry. The results showed that, at the end of 125 days of incubation, the 32‰ salinity addition reduced the cumulative mineralization of forest and agroforestry types by 28.41% and 34.35%, respectively, compared to the 0‰ salinity addition. Soil C mineralization in the three different land-use types was highly correlated with the active C fractions of readily oxidizable C (ROC), dissolved organic C, and microbial biomass C (MBC) in the soil, with the standardized coefficients of multivariate linear regression reaching 0.67 for MBC in the wetland and −0.843 for ROC in the forest. Under long-term salinity additions, increased salinity would reduce the microbial respiratory quotient value by inhibiting β-glucosidase activity, thus indirectly affecting the rate of CO2 release. With added salinity, the mineralization of non-saline soil was more susceptible to the inhibitory effect of salinity, whereas the mineralization of salinized soil was more controlled by soil C pools.

Can soil health in degraded woodlands of a semi-arid environment improve after thirty years?

In natural habitats, especially in arid and semi-arid areas that are fragile ecosystems, vegetation degradation is one of the most important factors affecting the variability of soil health. Studying physicochemical and biological parameters that serve as indicators of soil health offers important information on the potential risk of land degradation and the progression of changes in soil performance and health during recovery periods. This study specifically examines the impact of vegetation degradation on soil health indicators and the duration needed to improve the physical, chemical, and biological parameters in a semi-arid mountainous area site types with the dominance of Quercus macranthera Fisch & C.A. Mey and Carpinus orientalis Miller in northern Iran. In different years (2003, 2013, and 2023), litter and soil samples (at depths of 0–10, 10–20, and 20–30 cm) were collected in different types of degraded sites. Additionally, in 2023, a non-degraded site was chosen as a control and similar samples were collected. A total of 48 litter (12 samples for each of the study site types) and 144 soil (4 study site types × 3 depths × 12 samples) samples were collected. In order to investigate the spatial changes of soil basal respiration (or CO2 emission), which is involved in global warming, from each site type, 50 soil samples were taken along two 250-meter transects. The findings showed that litter P and Mg contents in the non-degraded site were 1.6 times higher than in degraded site types (2003). Following vegetation degradation, soil fertility indicators decreased by 2–4 times. The biota population was lower by about 80 % under the degraded site types (2003) than in the non-degraded site, and the density of fungi and bacteria in the degraded site types was almost half that of the non-degraded site types. Geostatistics showed the high variance (linear model) of CO2 emissions in areas without degradation. In addition, vegetation degradation significantly reduced soil carbon and nitrogen mineralization. Although soil health indicators under the degraded vegetation have improved over time (30 years), results showed that even thirty years is not enough for the full recovery of a degraded ecosystem, and more time is needed for the degraded area to reach the same conditions as the non-degraded site. Considering the time required for natural restoration in degraded site types, it is necessary to prioritize the conservation of vegetation and improve the ecosystem restoration process with adequate interventions.

Millennial-aged pyrogenic carbon in high-latitude mineral soils

Wildfires in the Arctic are producing pyrogenic carbon as product of incomplete biomass combustion. The storage and distribution of pyrogenic carbon in soils is poorly known, especially in carbon rich permafrost-affected mineral soils. Here, we extracted pyrogenic carbon in mineral soils from eleven forest sites across the North Canadian permafrost regions by hydrogen pyrolysis. We found pyrogenic carbon with millennial-scale ages that were older in continuous (1960–12,690 calibrated years before present) than in discontinuous (510–3560 calibrated years before present) permafrost-affected soils. In all cases, pyrogenic carbon showed longer residence times compared to bulk soil organic carbon. The proportions of pyrogenic carbon on total soil organic carbon were consistent at 6.9 ± 0.5% of total soil organic carbon. Thus, pyrogenic carbon forms a significant component of the total soil organic carbon and climatic as well as soil factors control the long residence times of pyrogenic carbon in vulnerable high-latitude forest mineral soils.