Understanding soil organic carbon (SOC) distribution and its environmental controls in permafrost regions is essential for achieving carbon neutrality and mitigating climate change. This study examines the spatial pattern of SOC and its drivers in the Headwater Area of the Yellow River (HAYR), northeastern Qinghai-Xizang Plateau (QXP), a region highly susceptible to permafrost degradation. Field investigations at topsoils of 86 sites over three summers (2021-2023) provided data on SOC, vegetation structure, and soil properties. Moreover, the spatial distribution of key permafrost parameters was simulated: temperature at the top of permafrost (TTOP), active layer thickness (ALT), and maximum seasonal freezing depth (MSFD) using the TTOP model and Stefan Equation. Results reveal a distinct latitudinal SOC gradient (high south, low north), primarily mediated by vegetation structure, soil properties, and permafrost parameters. Vegetation coverage and above-ground biomass showed positive correlation with SOC, while soil bulk density (SBD) exhibited a negative correlation. Climate warming trends resulted in increased ALT and TTOP. Random Forest analysis identified SBD as the most important predictor of SOC variability, which explains 38.20% of the variance, followed by ALT and vegetation coverage. These findings likely enhance the understanding of carbon storage controls in vulnerable alpine permafrost ecosystems and provide insights to mitigate carbon release under climate change.

Permafrost degradation, driven by rising temperatures in high-latitude regions, destabilizes previously sequestered soil organic carbon (OC), increasing greenhouse gas emissions and amplifying global warming. In these ecosystems, interactions with mineral surfaces and metal oxides, particularly iron (Fe), stabilize up to 80% of soil OC. This study investigates the mechanisms of Fe solubilization and OC release across a permafrost thaw gradient in Stordalen, Abisko, Sweden, including palsa, intermediate, and highly degraded permafrost stages. By integrating geophysical measurements-including relative elevation, thaw depth, soil water content, and soil temperature with redox potential and soil pore water chemistry, we identify the environmental conditions driving iron and organic carbon release into soil pore waters with permafrost degradation. Our results show that combining relative elevation, thaw depth, soil water content, soil pore water pH, and soil pore water conductivity with shifts in vegetation species enables very-high-resolution detection of permafrost degradation at submeter scales, distinguishing intact from degraded permafrost soils. We show that small-scale changes in thaw depth and water content alter soil pH and redox conditions, driving the release of Fe and dissolved organic carbon (DOC) and promoting the formation of Fe-DOC complexes in soil pore water. The amount of exported Fe-DOC complexes from thawed soils varies with the stage of permafrost degradation, and the fate of Fe-DOC complexes is likely to evolve along the soil-stream continuum. This study highlights how environmental conditions upon thaw control the type of Fe-DOC association in soil pore waters, a parameter to consider when quantifying what DOC is available for microbial and photo-degradation in aquatic systems which are significant sources of greenhouse gas emissions across Arctic landscapes.

Simple Summary The enzymic latch and iron gate theories represent two prevailing and contrasting mechanisms governing ecosystem carbon stability: the former via a phenolics accumulation mediated biochemical cascade that suppresses hydrolytic enzyme activity, and the latter via an abiotic pathway where ferrous iron oxidation suppresses phenol oxidase activity and promotes iron-bound soil organic carbon formation. Therefore, deciphering the stabilization mechanisms for the vast carbon stocks in permafrost peatlands represents a central challenge for climate change projections. In this study, we assessed the spatial distribution and interrelationships of peatland soil extracellular enzyme activities, iron phases, and iron-bound soil organic carbon across three permafrost zones in the Great Hing'an Mountains. Contrary to the enzymic latch mechanism, our data revealed that hydrolytic enzyme activities (beta-glucosidase, cellobiohydrolase, and beta-N-acetylglucosaminidase) were neither negatively correlated with phenolics nor positively correlated with phenol oxidase activity. Instead, iron emerged as the central regulator, with a positive correlation between ferrous iron and phenol oxidase activity and with ferric iron stabilizing soil organic carbon through co-precipitation. Our results highlighted that permafrost degradation could poses a threat to the dominant iron gate carbon sequestration mechanism in peatlands, potentially triggering a positive climate feedback.Abstract Distinct paradigms, such as the enzymic latch and iron gate theories, have been proposed to elucidate SOC loss or accumulation, but their relative significance and whether they are mutually exclusive in permafrost peatlands remain unclear. To address this, we evaluated their relative importance and identified the dominant factors controlling SOC stability. Therefore, we employed a space-for-time substitution approach across a permafrost gradient (continuous, discontinuous, and isolated) by systematically quantifying extracellular enzyme activities, iron (Fe) phases, and iron-bound soil organic carbon (Fe-SOC) at various depths (0-10, 10-30, and 30-50 cm) in peatlands. Our results did not support the enzymic latch theory, with hydrolytic enzyme activities (beta-glucosidase (BG), cellobiohydrolase (CBH), and beta-N-acetylglucosaminidase (NAG)) showing positive correlations with phenolics but negative correlations with phenol oxidase (PHO) activity. However, ferrous iron (Fe(II)) was significantly positively correlated with PHO activity, and ferric iron (Fe(III)) stabilized SOC through co-precipitation with it to form Fe-SOC, supporting the iron gate theory. Moreover, Fe-SOC decreased from the continuous to the isolated permafrost zone, and with soil depth from 0-10 cm to 30-50 cm. Partial least squares path modeling (PLS-PM) analysis indicated that Fe(III) directly and indirectly (via Fe-SOC and phenolics) affected SOC. Our study demonstrated the primacy of the iron gate mechanism in controlling carbon stability in the Great Hing'an Mountains permafrost peatlands, providing new insights for projecting carbon-climate feedback.

Soil organic carbon (SOC) plays a critical role in global carbon cycling and climate regulation, particularly in high-altitude permafrost regions. However, the impact of altitudinal gradients of alpine shrubs on SOC fractions remains poorly understood. In this study, we evaluated the rhizosphere SOC fractions and microbial biomass of Potentilla parvifolia along an altitudinal gradient (3,204, 3,350, 3,550, and 3,650 m). Our findings revealed that P. parvifolia significantly increased gram-positive bacterial and fungal biomass at medium and low altitudes (3,204, 3,350, and 3,550 m), enhancing the contribution of mineral-associated organic carbon (MAOC) to total SOC compared to bare soil. Moreover, SOC accumulation was primarily driven by the buildup of microbial necromass carbon, particularly fungal necromass carbon, within the MAOC fraction. These results improve our understanding of how altitudinal gradients influence SOC dynamics and microbial mechanisms, providing a scientific basis for developing effective bioprotection strategies to conserve high-altitude ecosystems under global climate change.IMPORTANCEThis study addresses critical knowledge gaps in understanding how altitudinal variation of shrubs affects soil carbon dynamics in the Qilian Mountains' seasonal permafrost. Investigating the redistribution between particulate organic carbon and mineral-associated organic carbon, along with microbial necromass (fungal vs bacterial), is vital for predicting alpine carbon-climate feedbacks. Shrub encroachment into higher elevations may alter vegetation-derived carbon inputs and decomposition pathways, potentially destabilizing historically protected permafrost carbon stocks. The unique freeze-thaw cycles in seasonal permafrost likely modulate microbial processing of necromass into stable carbon pools, a mechanism poorly understood in cold biomes. By elucidating altitude-dependent shifts in carbon fractions and microbial legacy effects, this research provides mechanistic insights into vegetation-mediated carbon sequestration under climate change. Findings will inform models predicting permafrost carbon vulnerability and guide alpine ecosystem management strategies in this climate-sensitive headwater region critical for downstream water security.

Alpine tundra ecosystems, like their arctic counterparts, have historically been the sites of considerable soil organic carbon (SOC) storage due to climatic factors that suppressed microbial activity. While climatic factors are important, heterotopic soil respiration (and SOC storage) may be influenced by a range of soil characteristics. In this study, we measured soil respiration, soil temperature, soil moisture, soil nutrient concentrations, soil pH, and soil texture in 4 alpine tundra sites located in Rocky Mountain National Park, Colorado, USA from June 2015 - September 2021. We also used geospatial modeling to visualize predicted climate changes in this system over the 21st century. Finally, we measured SOC concentrations over the seven-year study. We found that soil respiration was significantly correlated with soil temperature, soil moisture, and soil texture. All other parameters were not significantly correlated with soil respiration. We also found that SOC concentrations did not change significantly over the course of the seven-year study. The predictive models show that by the end of the century, over the majority of the park, the mean maximum air temperature will increase, the amount of snowfall will decrease, soil moisture will decrease, and the number of snow-free days will increase. These results suggest that SOC is not currently being lost from this system at a high rate. In addition, it appears that with a changing climate, soil respiration may increase with warming, but the overall increase may be limited by decreased soil moisture and in some cases, high soil temperatures.

Southern boundary areas of high-latitude permafrost regions may represent the future permafrost temperature regimes; therefore, understanding the carbon stocks and their stability in these systems can shed light on the permafrost carbon cycle under a warming climate. In this study, we sampled soils at three sites representing three differing land covers (forest swamp, dry forest, and shrub swamp) located in the southern boundary area of a high-latitude permafrost region and investigated their carbon fractions and the relationships of these fractions with soil physicochemical parameters in the active and permafrost layers. The results show that the proportion of active carbon is higher in permafrost than in the active layer under forest swamp and dry forest, implying that carbon pools in the permafrost are more decomposable. However, in shrub swamp, the active carbon components in the permafrost layer are lower than in the active layer. Soil pH and water content are the most significant factors associated with soil organic carbon concentration both in the active layers and in the permafrost layers. Our results suggest that, although soil organic carbon concentrations largely decrease with depth, the proportion of the forest swamp, dry forest labile carbon is higher in the permafrost layer than in the active layer and that the vertical distribution of labile carbon proportions is related to land covers.

Uncertainties in carbon storage estimates for disturbance-prone dryland ecosystems hinder accurate assessments of their contribution to the global carbon budget. This study examines the effects of land-use change on carbon storage in an African savanna landscape, focusing on two major land-use change pathways: agricultural intensification and wildlife conservation, both of which alter disturbance regimes. By adapting tree inventory and soil sampling methods for dryland conditions, we quantified aboveground and belowground carbon in woody vegetation (AGC and BGC) and soil organic carbon (SOC) across these pathways in two vegetation types (scrub savanna and woodland savanna). We used Generalized Additive Mixed Models to assess the effects of multiple environmental drivers on AGC and whole-ecosystem carbon storage (C-total). Our findings revealed a pronounced variation in the vulnerability of carbon reservoirs to disturbance, depending on land-use change pathway and vegetation type. In scrub savanna vegetation, shrub AGC emerged as the most vulnerable carbon reservoir, declining on average by 56% along the conservation pathway and 90% along the intensification pathway compared to low-disturbance sites. In woodland savanna, tree AGC was most affected, decreasing on average by 95% along the intensification pathway. Unexpectedly, SOC stocks were often higher at greater disturbance levels, particularly under agricultural intensification, likely due to the preferential conversion of naturally carbon-richer soils for agriculture and the redistribution of AGC to SOC through megaherbivore browsing. Strong unimodal relationships between disturbance agents, such as megaherbivore browsing and woodcutting, and both AGC and C-total suggest that intermediate disturbance levels can enhance ecosystem-level carbon storage in disturbance-prone dryland ecosystems. These findings underline the importance of locally tailored management strategies-such as in carbon certification schemes-that reconcile disturbance regimes in drylands with carbon sequestration goals. Moreover, potential trade-offs between land-use objectives and carbon storage goals must be considered.

The economic benefits of rice-wheat (RW) and rice-oilseed rape (RO) rotation in China are low. By contrast, the rice-edible mushroom Stropharia rugosoannulata (RE) rotation yields significantly higher economic benefits than RW and RO rotations. Furthermore, RE rotation can avoid air pollution caused by rice straw burning and has been widely adopted in China. Nevertheless, it remains unclear how the rotation affects CH4 and N2O emissions and global warming potential. Herein, three rice-based rotations, including RW, RO and RE rotations, were conducted in central China. The RE rotation resulted in the lowest CH4 emission from the winter crop season as well as the lowest annual N2O emission from the rice seasons among the three rotations. Moreover, compared with the RW and RO rotations, the RE rotation significantly increased the soil organic carbon content by 30.2 % and 31.2 %, and the rice yield by 16.0 % and 17.0 %, respectively. Hence, the RE rotation significantly reduced the net global warming potential by 2008.4 % and 696.5 % compared with the RW and RO rotations, respectively. Furthermore, the RE rotation improved soil fertility compared with the other two rotations. Although the RE rotation required the highest agricultural input among the three rotations, it contributed to the highest net ecosystem economic profits owing to its highest agricultural income and lowest environmental damage cost. Thus, RE rotation is an effective rice-based rotation that can use rice straws to reduce the net global warming potential and increase economic benefits and soil fertility. Therefore, RE rotation may serve as an alternative strategy for achieving sustainable agricultural production in winter fallow areas of the rice-upland region in Yangtze River Basin, China.

Mucilage offers several beneficial functions for soils, yet its impact on soil mechanical behavior remains underexplored. This study investigated the effects of chia seed mucilage on the plasticity index (under normal conditions) and penetration resistance (under compaction) of sandy clay loam soils with differing soil organic carbon (SOC) levels from Akhtar Abad (SOC = 1.6%) and Najm Abad (SOC = 0.6%) in northern Iran. Four mucilage concentrations (0, 1 g kg-1, 3 g kg-1, 5 g kg-1) and three compaction pressures (100 kPa, 300 kPa, 600 kPa) were used. We found that mucilage significantly increased the plasticity index, with a 5.8% increase at 1 g kg-1 in the Najm Abad soil and 2.6%-3% increases at higher concentrations in the Akhtar Abad soil. At a concentration of 3 g kg-1, soil penetration resistance in the Akhtar Abad soil increased by 0.9 MPa and 1.6 MPa at compaction pressures of 300 kPa and 600 kPa, respectively. In the Najm Abad soil, a concentration of 5 g kg-1 led to increases of 0.7 MPa and 1.7 MPa at compaction pressures of 300 kPa and 600 kPa, respectively. No significant relationship was found between soil penetration resistance and soil plasticity index. The mucilage-induced increase in soil plasticity may hinder soil workability, especially when tillage occurs immediately after crop harvest. Mucilage can also increase soil resistance to root penetration in areas compacted by heavy machinery. To mitigate these risks, we recommend performing tillage and machinery operations in both agricultural and forest ecosystems during dry periods, when mucilage is less active, to minimize its negative impact on soil workability and compaction.

Straw return is widely acknowledged as a crucial strategy for enhancing soil fertility and increasing crop yields. However, the continuous addition of straw, its slow decomposition, and retention can hinder crop growth. Therefore, it is essential to elucidate the characteristics of the crop straw decomposition. This study aims to explore the alterations in straw decomposition rates, as well as the content and structure of organic components, under the combined application of swine manure and corn straw in the broken skin yellow soil of black soil over time. The findings revealed that the straw decomposition rates in all treatments increased rapidly in the early stage, gradually slowed down and stabilized in the later stage. The decomposition rates of cellulose and hemicellulose were generally consistent with those of straw, while lignin decomposed more rapidly in the middle and later stages. Notably, the decomposition rate of straw and its components was significantly higher under the combined application of swine manure and biochar compared to other treatments, with decomposition rates of straw, cellulose, hemicellulose, and lignin recorded at: 66.16%, 63.38%, 61.16% and 47.96%, respectively, after 360 days. This treatment exhibited the most substantial damage to the apparent structure of corn straw over time, and it resulted in lower C/N ratios and the most pronounced decrease in the intensity of absorption peaks. Among all the treatments, the alkyl carbon/alkoxy carbon ratio was highest in the SCZ treatment, indicating that the addition of swine manure and biochar can significantly enhance straw decomposition. Correlation analysis revealed that the decomposition rates of straw, cellulose, hemicellulose, and lignin were significantly and positively correlated with the rates of alkyl carbon, aromatic carbon, and phenolic carbon in the organic functional groups of straw residues, and significantly negatively correlated with alkoxy carbon. The study suggested that the combined application of straw, swine manure and biochar in the field can effectively promote the decomposition of corn straw. Our findings provided insights into the efficient utilization of various exogenous conditioners, serving as a scientific basis for accelerating straw decomposition and enhancing nutrient utilization.