Protection Of Soil Organic Carbon Research Articles

Soil Amendment Combining Bentonite and Maize Straw Improves Soil Quality Cropped to Oat in a Semi-Arid Region

Soil amendments have been proposed as an effective way to enhance soil carbon stocks on degraded soils, particularly in dryland farming areas. Soil organic carbon (SOC) plays an important role in improving soil quality, and soil aggregates are known to be crucial in sequestering and protecting SOC. However, how aggregation and protection of SOC by aggregates respond to a single application of bentonite combined with maize straw remains unknown, especially in the sandy soil of a semi-arid region. A three-year field experiment with four treatments [no amendment (CK), maize straw amendment addition only (T1, 6 Mg ha−1), bentonite amendment addition only (T2, 18 Mg ha−1), and maize straw combined with bentonite amendment (T3, 6 Mg ha−1 maize straw plus 18 Mg ha−1 bentonite)] was conducted in the Loess Plateau of China to assess the effects of bentonite and maize straw on aggregation and SOC. The results indicated that soil bulk density decreased by 2.72–5.42%, and soil porosity increased by 3.38–8.77% with three years of T3 application, especially in the 20–40 cm layer, compared with CK. T3 increased the amount of C input, SOC stock, and SOC stock sequestration rate by 1.04 Mg ha−1 y−1, 0.84–1.08 Mg ha−1, and 0.49 Mg ha−1 y−1, respectively, and it increased the mass proportions and aggregate-associated C stock of >0.25 mm aggregates by 1.15–2.51- and 1.59–2.96-fold compared with CK. Correlation analysis showed a positive correlation of total SOC stock with the C concentration of >2 mm, 0.25–2 mm, and 0.053–0.25 mm aggregates. Aggregates of various sizes in sandy soils have the potential for greater SOC stock. Our findings suggest that the application of maize straw (6 Mg ha−1) combined with bentonite (18 Mg ha−1) would be an effective management strategy to enhance the bulk soil C pools by improving the soil structure and thereby improving soil fertility.

Shining a Light on How Soil Organic Carbon Behaves at Fine Scales under Long-Term Elevated CO2: An 8 Year Free-Air Carbon Dioxide Enrichment Study.

Building and protecting soil organic carbon (SOC) are critical to agricultural productivity, soil health, and climate change mitigation. We aim to understand how mechanisms at the organo-mineral interfaces influence SOC persistence in three contrasting soils (Luvisol, Vertisol, and Calcisol) under long-term free air CO2 enrichment conditions. A continuous wheat-field pea-canola rotation was maintained. For the first time, we provided evidence to a novel notion that persistent SOC is molecularly simple even under elevated CO2 conditions. We found that the elevated CO2 condition did not change the total SOC content or C forms compared with the soils under ambient CO2 as identified by synchrotron-based soft X-ray analyses. Furthermore, synchrotron-based infrared microspectroscopy confirmed a two-dimensional microscale distribution of similar and less diverse C forms in intact microaggregates under long-term elevated CO2 conditions. Strong correlations between the distribution of C forms and O-H groups of clays can explain the steady state of the total SOC content. However, the correlations between C forms and clay minerals were weakened in the coarse-textured Calcisol under long-term elevated CO2. Our findings suggested that we should emphasize identifying management practices that increase the physical protection of SOC instead of increasing complexity of C. Such information is valuable in developing more accurate C prediction models under elevated CO2 conditions and shift our thinking in developing management practices for maintaining and building SOC for better soil fertility and future environmental sustainability.

Warming Leads to Changes in Soil Organic Carbon Molecules Due to Decreased Mineral Protection.

Climate change affects the content and composition of soil organic carbon (SOC). However, warming-induced changes in the SOC compounds remain unknown. Using nuclear magnetic resonance spectroscopy, molecular mixing models, and Fourier transform ion cyclotron resonance mass spectrometry, we analyzed the variations and relationships in molecular compounds in Mollisol with 10-56 g C kg-1 soil-1 by translocating soils under six climate regimes. We found that increased temperature and precipitation were negatively correlated with carbohydrate versus lipid and lignin versus protein. The former was consistent across soils with varying SOC contents, but the latter decreased as the SOC content increased. The carbohydrate-lipid correlations were related to dithionite-citrate-extractable Fe, while the lignin-protein correlations were linked to changes in moisture and pyrophosphate-extractable Fe/Al. Our findings indicate that the reduction in the mineral protection of SOC is associated with molecular alterations in SOC under warming conditions.

Fungi are more important than bacteria for soil carbon loss through priming effects and carbon protection through aggregation

Plant inputs from root exudates and litter can improve soil aggregation and enhance soil organic carbon (SOC) content, but they can also increase SOC decomposition referred to as the priming effect. While bacteria and fungi are considered as key microbes for organic matter decomposition, their role in decomposing plant inputs and SOC, and their contribution to forming aggregates and SOC protection is still not fully understood. We conducted a 16-day incubation study to investigate the role of bacteria and fungi on decomposition and protection of C derived from glucose (labile C as a surrogate for root exudates) and wheat root biomass added to soil. Bronopol and captan were used to suppress bacterial and fungal activity, respectively, in the soil. Because glucose and wheat root biomass were enriched in 13C, we were able to estimate their decomposition and priming effect, microbial C use efficiency (CUE), and recovery in different aggregate size classes. As expected, the decomposition of both substrates was reduced significantly when biocides were added, and the decomposition rate of glucose was significantly higher than of wheat root biomass. Fungi were more important than bacteria in causing a priming effect, as indicated by the reduced SOC decomposition in the presence of substrates when captan was added. The mean weight diameter of aggregates at the end of the incubation was significantly reduced when captan was added, either alone or in combination with bronopol, independent of substrate type, suggesting that fungi also played an important role in soil aggregation. However, recovery of C derived from wheat root biomass in macroaggregates was highest when both biocides were added, suggesting that decomposition by both bacteria and fungi may have outweighed the protection of wheat C in new macroaggregates. While we observed variation in the microbial CUE among substrate and biocide treatments, we found no relationship with soil aggregation. We conclude that both bacteria and fungi were important for decomposition of added substrates to the soil, but that fungi can play a larger role in both soil C loss through priming effects and C protection through aggregation.

Disentangle the drivers of soil organic carbon mineralization and their temperature sensitivity in both topsoil and subsoil: Implication of thermal stability and chemical composition

Information about the temperature dependence of soil organic carbon (SOC) mineralization is important to predict the possible carbon (C) release from the terrestrial ecosystem facing global warming. However, the way in which SOC quality and mineral protection of SOC affects mineralization rates and their response to increasing temperature remains poorly understood. Here, we focused on investigating thermal stability and chemical composition of soils which differed greatly with the type and extent of organo-mineral associations, and revealing their implications for SOC mineralization. Chemical composition and thermal stability of SOC were analyzed with 13C nuclear magnetic resonance spectroscopy (13C NMR) and simultaneous thermogravimeteric analysis and differential scanning calorimetry (TG-DSC), respectively. Soil mineralization and its temperature sensitivity (Q10) were assessed by incubating soils at 15 and 25 °C for 90 days.Our results showed that SOC of subsoil was more biologically stable, but exhibited higher temperature sensitivity than those of topsoil. Significant differences in chemical composition and thermal stability of SOC were detected across soils developed from four parent materials but not between two soil layers, and indicators obtained from the two techniques showed apparent associations with depth-specific SOC mineralization rates. Increase in SOC mineralization rates at two incubation temperatures and two soil layers were observed when the soils were characterized by higher percentage of labile SOC fractions (i.e., O-alkyl C and organic carbon oxidized during exothermic reactions). The Q10 values of topsoil were positively and mostly related to the percentage of Alkyl C. In addition to notable relationships with chemical composition, the Q10 values of subsoil were positively correlated with Exo1/Exo2 ratios and Energy density values, and negatively correlated with TG-50. It was interesting to note that thermal stability was possibly as a function of soil texture and total oxides. Results from VPA analysis further revealed that SOC mineralization rates at two soil layers and Q10 of topsoil were mainly driven by SOC quality, while it was related to both SOC quality and chemical protection for subsoil, implying that factors controlling the temperature sensitivity of SOC mineralization were depth-specific. Altogether, substrate accessibility as a function of chemical composition and chemical protection would play vital role in determining the feedbacks of the subsoil SOC pool to the future climate warming.

The Different Roles of Mineralogy in Soil Organic Carbon Accumulation in Northern and Southern China

The sequestration of soil organic carbon (SOC) through mineral protection is an important approach to mitigating climate change. However, the effect of mineral composition on SOC stability is unclear at regional scales. In this study, we investigated the relationship between mineralogy and SOC in Alfisol and Mollisol from southern and northern regions of China. We analyzed soil at two layers for its SOC fractions, mineralogical characteristics and functional groups. It was found that the majority of SOC was stored as mineral-associated organic C (MAOC), which had higher δ13C values and narrower C/N ratios compared to particulate organic C. In Mollisol, the proportion of MAOC and the abundance of aromatic C were higher than that in Alfisol, while polysaccharide C was lower. Compared to Alfisol, Mollisol was dominated by illite, and had significantly (p < 0.05) lower iron (Fe) and aluminum (Al) sesquioxides contents. The SOC content was positively correlated with illite in Mollisol, and with Fe and Al sesquioxides in Alfisol. The random forest model identified sesquioxides as the most important determinant of SOC accumulation (36%), followed by SOC fractions (18%) and functional groups (18%). In summary, our study suggests that SOC protection through mineralogy depends more on the composition of the host minerals, and not just on the clay content, and aromatic C is also important in the stabilization of SOC.

Long-Term Effect of Prescription-Based Fertilization on Culturable Soil Microorganisms and Carbon Dynamics in Northwest Himalayas

ABSTRACT The different approaches of fertilizer application can play an important role in altering soil biological properties, organic carbon retention, and its dynamics. The mechanisms implicit in the long-term accumulation and protection of soil organic carbon and improvement in soil biological environment, however, have not been well documented for maize crop cultivated in acid soils of the Northwest Himalayas. Based on a 13-year experiment, the effects of prescription-based fertilization on soil culturable microorganisms and soil carbon dynamics were investigated under a continuous maize cropping at Palampur, India. The experiment was initiated during 2007 in randomized block design (RBD) with 8 treatments which were replicated three times. The soil of the experimental site was acidic, having silty clay loam texture and classified taxonomically as “Typic Hapludalf.” The surface soil samples from 0.15 m depth were drawn after the harvest of maize crop in 2019 for estimation of culturable soil microorganisms and carbon dynamics. Based on soil-test crop response approach, the application of 110 kg ha−1 nitrogen and 82 kg ha−1 phosphorus with 5 Mg ha−1 farmyard manure (FYM) for attaining the target yield of 4.0 Mg ha−1 of maize recorded significantly highest population of soil bacteria (40.7 × 105 CFU g−1 soil), fungi (57.0 × 105 CFU g−1 soil), actinomycetes (38.2 × 105 CFU g−1 soil), microbial biomass carbon (147.2 µg g−1), dehydrogenase enzyme activity (4.3 µg TPF g−1 hr−1), different fraction of organic carbon, i.e. very labile (4.6 g kg−1), labile (2.60 g kg−1), less labile (2.70 g kg−1), non-labile (2.94 g kg−1), soil organic carbon (8.9 g kg−1), total soil organic carbon (11.8 g kg−1), total carbon stock (16.1 t ha−1), carbon sequestration (3.24 t ha−1) and carbon sequestration rate (1.24t ha−1year−1) when compared with control plot. Based on the data associated with microbial soil environment and carbon dynamics, it was inferred that application of prescription-based fertilizers along with farmyard manure for a longer period not only improved population of soil culturable microorganisms but also enhanced soil carbon sequestration and minimized carbon di-oxide (CO2) emission to atmosphere.

Perennial intermediate wheatgrass accumulates more soil organic carbon than annual winter wheat – a model assessment

PurposePerennial crops have been suggested as a more sustainable alternative to the currently most common cropping systems. Compared with annual plants, perennial plants produce more biomass and have deeper roots, and are expected to lead to higher soil organic carbon (SOC). This hypothesis, however, has not been well tested for grain crops.MethodsUsing perennial intermediate wheatgrass (IWG, Thinopyrum intermedium) and annual winter wheat (Triticum aestivum) as focal species, and native grassland as reference, we quantified the SOC accumulation via a process-based model, describing water and heat exchanges and carbon-nitrogen cycling in the canopy and soil to a depth of 2 m. The model includes C fixation via photosynthesis, plant biomass growth and litter production, physical protection of SOC, depolymerisation, C mineralisation, nitrification, denitrification, microbial growth, and necromass turnover in the soil. While of general applicability, we considered a sandy loam under warm-summer humid continental climate.ResultsFollowing a conversion from native grassland, IWG reduced SOC losses by at least 38%, especially in the particulate organic carbon (POC) pool, within the top 2 m of soil, compared with annual wheat. Soil microbial biomass and soil respiration were higher in IWG than annual wheat. Shifting from annual wheat to high photosynthetic capacity IWG increased SOC by about 33 g C m−2 y−1 (averaged over a 4-year continuous IWG cropping), with a large fraction of SOC gain stemming from restoring POC.ConclusionCompared with annual grains, perennial grains can increase soil carbon sequestration and maintain SOC at levels nearer to that of native grasslands.

Contribution of soil aggregate particle size to organic carbon and the effect of land use on its distribution in a typical small watershed on Loess Plateau, China

Soil organic carbon (SOC) is an important pool in the global carbon cycle, playing a vital role in moderating atmospheric CO2 concentrations. Soil is the largest carbon pool in terrestrial ecosystems and, as the basic unit of soil structure, soil aggregates are key to protecting soil carbon pools. However, the influence of soil aggregate particle size, SOC distribution, and the contribution of different particle sizes to SOC is still unclear, particularly under different land use types. In this study, soil samples were collected from five land use types (slope farmland (SF), forest (FL), grassland (GL), shrubland (SL), and terraced field (TF)) in a typical small watershed in the Loess Plateau, China. We analyzed the soil aggregate particle size, composition, and stability after dry and wet sieving, SOC content of different particle sizes in aggregates, and the effects of different aggregate particle sizes and land use on the distribution of SOC. The results showed that, the surface soil (0 ∼ 20 cm) water-stable aggregates were relatively stable, particularly under FL, the mean weight diameter (MWD) value was 2.16 mm. Deep soil (40 ∼ 60 cm) non-water stable aggregates were more stable, and GL was optimal, the MWD value was 3.94 mm. SOC and total nitrogen (TN) were significantly correlated with water-stable aggregate stability indicators (p < 0.01). The SOC content in the small aggregates (0.25 ∼ 2 mm) was the highest and lowest in the microaggregates (<0.25 mm) under different land use. The carbon/nitrogen (C/N) ratio of microaggregates was significantly higher in SF (the C/N ratio was 23.17) and GL (the C/N ratio was 31.04) than in other land uses (p < 0.01) in the 20–40 cm soil layer. In surface soil, small aggregates contributed>50% to SOC in SF and TF. In deep soil, small aggregates under all five land uses made the largest contribution rate to SOC at 57%. These findings indicate that carbon sequestration in the study area can be improved by a combination of appropriate soil management with ecological construction to increase the content of small aggregates, strengthen the fixation and protection of SOC, and reduce carbon emissions in the soil.

Combination of mineral protection and molecular characteristics rather than alone to govern soil organic carbon stability in Qinghai-Tibetan plateau wetlands

Wetlands in the Yarlung Tsangpo River Basin (YTR) on the Qinghai-Tibet Plateau provide immense soil organic carbon (SOC) storage, which is highly susceptible to climate warming and requires urgent deciphering SOC stabilization mechanisms of long-term protection of SOC against decomposition. Conflicting views exist regarding whether persistent SOC is controlled by molecular features or by mineral protection. As such, this study quantified SOC stability using two thermal indices (TG-T50, and DSC), described molecular features of SOC using pyrolysis-gas chromatography-mass spectrometry, and measured SOC protection by minerals using a chemical extraction method. Results indicated SOC of topsoils had higher thermal stability, with TG-T50 and DSC-T50 of 337.61 °C and 384.58 °C, than that of subsoils with TG-T50 and DSC-T50 of 337.32 and 382.67 °C, respectively. We found subsoils had significantly higher proportions of aliphatic and aromatic compounds, while existed higher SOC associated with minerals. It seemed SOC stabilization differed with soil depths, in which mineral protection dictated SOC thermal stability in topsoils while molecular features posed a more important constraint on SOC stabilization in subsoils. Overall, our findings support the hypothesis of physical and chemical protection but emphasized that SOC thermal stability largely depended on to extent of the combination between molecular features and mineral protection, which explained 55% in topsoils and 73% in subsoils, respectively.

Interactions of soil quality, ages of alluvial fans, and mechanisms controlling total soil organic carbon dynamics

So far, no studies have tested how alluvial fan aging and associated geomorphological differences can affect the mechanisms that control soil organic carbon (SOC) dynamics. In order to understand the SOC dynamics, we quantified the relationship between soil quality (SQ) indicators and alluvial fans aging over area of about 10,000 km2 in north-eastern Iran, using a minimum data set (MDS) and regression analyses. Twenty seven soil attributes and weathering indices were measured at 90 old and young fans. Total SOC and its fractions were found as the key indicators of the MDS. Despite the higher content of SOC in younger fans (6.25 – 7.11 g kg−1), they exhibited a lower value of SQ (0.35 – 0.42). Younger fans had a low content of fine-sized pedogenic oxides, and, thus, a lower sorption potential, giving rise to a lower ability for stabilising SOC. The higher content of SOC in younger fans was due to an accumulation of coarse particulate organic carbon. Long-term exposure of the older surfaces to weathering caused a statistically significant increase in the chemical index of alteration (57.94 – 72.32 %), chemical index of weathering (64.3 – 77.2 %), the carbon size fraction 53 – 250 µm (2.66 – 5.56 g kg−1), the dithionite-extractable Al (48.4 – 59.2 g kg−1) and Fe (21.5 – 25.7 g kg−1) oxalate-extractable Al (25.6 – 32.7 g kg−1) and Fe (9.5 – 13.0 g kg−1). These characteristics promote physical protection of SOC against microbial decomposition. Alluvial fan aging leads to geomorphological differences in terms of the weathering degree, processes of flooding, inundation, and erosion, contributing to high variability of the SOC dynamics. A proper understanding of the relationships between the age evolution of landforms and associated variations in mechanism regulating the preservation and stability of soil C can help to develop new perspectives for geo-conservation and restoration efforts.

Pore structure characteristics and organic carbon distribution of soil aggregates in alpine ecosystems in the Qinghai Lake basin on the Qinghai-Tibet Plateau

Soils in alpine ecosystems serve as important carbon sinks. Soil aggregates provide physical protection to soil organic carbon (SOC) and pore networks of them can greatly influence SOC sequestration. However, previous studies mainly focused on SOC dynamics at ecosystem or regional scale in cold alpine regions. The lack of quantification of alpine soil aggregate pore structure limits our understanding of SOC sequestration mechanisms of alpine soil. In this study, three typical alpine ecosystems in the Qinghai Lake basin of Qinghai-Tibet Plateau (QTP) were selected: Kobresia pygmaea meadow (KPM), Potentilla fruticosa shrubland (PFS), and Achnatherum splendens steppe (ASS). Soil pore structure, SOC and their relationships in aggregates were examined through sieving procedure and X-ray computed tomography (CT) scanning. The results showed that the mass proportion of small macroaggregates (SMA, 0.25–2 mm) was highest and they accounted for 36–51% of all aggregate fractions in the above three alpine ecosystems. The pores of soil aggregate were found to be dominated by micropores (<30 μm), which accounted for over 90% of the pore numbers. Aggregates of the ASS ecosystem had highest mean pore volume (7.761 × 10³ μm3 in average) while soil aggregates of the KPM ecosystem had the highest pore number density (4.137 × 10-5 no. μm−3 in average). The highest total organic carbon (TOC) content was mostly observed in the mA (microaggregates, 0.053–0.25 mm) fractions in the three ecosystems. Particulate organic carbon (POC) content was higher than mineral-associated organic carbon (MAOC) content of aggregates. Pores of < 15 μm served as indirect indicators for SOC protection in soil aggregates. Pores of 15–30 μm in aggregates might provide voids for SOC decomposition. TOC and MAOC content were positively correlated with pore surface area density while POC content was positively correlated with pore equivalent diameter and mean volume of aggregates. SOC was mainly affected by soil water content (SWC) in KPM and PFS ecosystems while it was mainly affected by soil particle compositions in the ASS ecosystems. Our results revealed the structural characteristics of aggregates of alpine soil and their relationships with the carbon storage function, which are helpful to understand the micro-scale mechanism of carbon sink of alpine soil.

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

AbstractMineral binding of organic carbon (OC) is one of the key mechanisms promoting soil organic carbon (SOC) persistence, which is vital for the long‐term sequestration of atmospheric carbon dioxide into soils. 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. Here, we analyzed OC bound to metal oxides (OCmetal) versus silicate clay (OCclay) in soils from contrasting environments (i.e., wetlands and uplands) using sequential dissolution by dithionite and hydrofluoric acid. We found that OCmetal% was higher than OCclay% in both wetlands and uplands, indicating the dominance of metal oxides in SOC protection. The sum of OCmetal% and OCclay% constituted a higher fraction of SOC in wetlands than uplands, suggesting an underappreciated role of mineral (in particular, metal oxide) protection in wetland SOC preservation. Furthermore, using lignin phenol analysis in tandem, ∼23% of lignin phenols were additionally released after the removal of silicate clay, providing a potential means to assess “hidden” lignin in mineral matrices. Given the wide use of lignin phenols as tracers for terrestrial plant‐derived OC, our results suggest that the contribution of terrestrial or plant‐derived carbon to sedimentary carbon stocks or mineral‐protected SOC deserves reassessment. These findings highlight the differential role of various soil minerals in the protection of SOC and its components in contrasting terrestrial environments, which warrants better recognition for understanding the distribution and dynamics of mineral‐protected SOC.

Relationship between carbon pool changes and environmental changes in arid and semi-arid steppe—A two decades study in Inner Mongolia, China

As the arid and semi-arid grassland with the most extensive distribution area in northern China, the carbon stored in Inner Mongolia (IM) grassland is highly susceptible to environmental changes. With the global warming and drastic climate changes, exploring the relationship between carbon pool changes and environmental changes and their spatiotemporal heterogeneity is necessary. This study estimates the carbon pool distribution of IM grassland during 2003–2020 by combining the measured below ground biomass (BGB) dataset, measured soil organic carbon (SOC) dataset, multi-source satellite remote sensing data products, and random forest regression modeling method. It also discusses the variation trend of BGB/SOC and its correlation with critical environmental factors, vegetation condition factors and drought index. The results show that the BGB/SOC in IM grassland was stable during 2003–2020, with a weak upward trend. The correlation analysis reveals that high temperature and drought environment were unfavorable for developing vegetation roots and would lead to a decrease in BGB. Furthermore, temperature rise, soil moisture decrease, and drought adversely effected grassland biomass and SOC in areas with low altitude, high SOC density, suitable temperature and humidity. However, in areas with relatively poor natural environments and relatively low SOC content, SOC was not significantly affected by environmental deterioration and even showed an accumulation trend. These conclusions provide directions for SOC treatment and protection. In areas where SOC is abundant, it is important to reduce carbon loss caused by environmental changes. However, in areas with poor SOC, due to the high carbon storage potential of grasslands, carbon storage can be improved through scientifically managing grazing and protecting vulnerable grasslands.

Land conversion impacts on soil macroaggregation, carbon sequestration and preservation in tree orchards located in Mediterranean environment (Spain)

Agricultural soils degradation is a global challenge that affects food security, climate change, environmental risks, and the loss of biodiversity and ecosystem services. In this on-farm study conducted in the Mediterranean mountain area of southern Spain, we used a natural area (NAT) as reference and compared the effect of three tree cropping systems – conventional olive (COL), organic olive (OLO) and organic almond (OAL)– on soil aggregation, aggregates-associated soil organic carbon and carbon preservation capacity. This was conducted to evaluate the hypothesis that the organic management system affects soil stability, soil organic carbon sequestration and soil organic carbon distribution among aggregate fractions. Soil samples were collected at five different depths (0–10, 10–20, 20–30, 30–40 and 40–50 cm depth) to analyse the management impacts on deeper soil layers. Aggregation indices showed an increase in the topsoil layers (0–10 and 0–20 cm depth) under organic managements with higher large macroaggregates (> 2000 µm) percentages in OLO (+10.9 % and 21.8 %) and OAL (+15.25 % and 28.5 %) respectively compared to COL. A significant decarbonization process was detected and the total carbon preservation capacity (0–50 cm depth) decreased from NAT (159.24 g kg—1) to cultivated plots, that stored a − 53.8 % OLO (73.45 g kg—1), − 66.3 % OAL (53.69 g kg—1) and − 70.4 % COL (47.22 g kg—1). In this regard, the management change from conventional to organic increased total carbon preservation capacity and caused a change in the distribution of soil organic carbon pool observed in a higher carbon content in large macroaggregates (+47.3 %). These findings indicate that organic farming affects not only to the soil organic carbon sequestration but also to the extent of soil organic carbon protection.

Greenhouse Gas Emissions from Soils Amended with Cornstalk Biochar at Different Addition Ratios.

Biochar addition has been recommended as a potential strategy for mitigating climate change. However, the number of studies simultaneously investigating the effects of biochar addition on CO2, N2O and CH4 emissions and sequentially global warming potential (GWP) is limited, especially concerning its effect on native soil organic carbon (SOC) mineralization. An incubation experiment was conducted to investigate soil physicochemical properties, CO2, N2O and CH4 emissions and GWP in the treatments with 0% (CK), 1% (BC1) and 4% (BC4) cornstalk biochar additions, and clarify the priming effect of biochar on native SOC mineralization by the 13C tracer technique. Generally, biochar addition increased soil pH, cation exchange capacity, SOC and total nitrogen, but decreased NH4+-N and NO3--N. Compared with CK, BC1 and BC4 significantly reduced CO2 emissions by 20.7% and 28.0%, and reduced N2O emissions by 25.6% and 95.4%, respectively. However, BC1 significantly reduced CH4 emission by 43.6%, and BC4 increased CH4 emission by 19.3%. BC1 and BC4 significantly reduced the GWP by 20.8% and 29.3%, but there was no significant difference between them. Biochar addition had a negative priming effect on native SOC mineralization, which was the reason for the CO2 emission reduction. The negative priming effect of biochar was attributed to the physical protection of native SOC by promoting microaggregate formation and preferentially using soluble organic carbon in biochar. The N2O emission decrease was rooted in the reduction of nitrification and denitrification substrates by promoting the microbial assimilation of inorganic nitrogen. The inconsistency of CH4 emissions was attributed to the different relative contributions of CH4 production and oxidation under different biochar addition ratios. Our study suggests that 1% should be a more reasonable biochar addition ratio for mitigating greenhouse gas emissions in sandy loam, and emphasizes that it is necessary to furtherly investigate nitrogen primary transformation rates and the relative contributions of CH4 production and oxidation by the 15N and 13C technique, which is helpful for comprehensively understanding the effect mechanisms of biochar addition on greenhouse gas emissions.

Aggregate-associated carbon contributes to soil organic carbon accumulation along the elevation gradient of Helan Mountains

Physically or biochemically protected soil organic carbon (SOC) can dampen microbial decomposition by reducing substrate availability, enhancing the stability of SOC. However, microbe-mediated changes in the physical and chemical compositions of SOC along an elevation gradient are poorly understood, especially in arid mountain environments. Here, soil samples from depths of 0–20 cm and 20–40 cm along five elevations ranging from 1380 to 2438 m in Helan Mountains were collected. We explored the effect of the soil microbial community and enzyme activities on the physical (via aggregate-associate C) and chemical compositions of SOC. The results showed that the amount of aggregate-associated C, the abundance of microbes and enzyme activities were significantly greater in the 0–20 cm than the 20–40 cm soil layer. The ratio of fungi to bacteria (F/B), aggregate-associated C, and cellobiohydrolase (CBH) activity increased with elevation. However, the highest proportion of aromatic C, total PLFA, β-1,4-glucosidase (BG), N-acetyl-β-glucosaminidase (NAG), leucine aminopeptidase (LAP), and alkaline phosphatase (AP) were found at the mid-elevation (2139 m), with a hump-shaped unimodal distribution pattern. This indicated that soil microbes at mid-elevation had the highest potential to decompose the relatively labile carbon compositions. CBH explained the most variations in the physical and chemical compositions of the SOC and had a significant effect on the macroaggregate- and silt and clay-associated C. Structural equation modeling (SEM) indicated that with an increase in elevation, F/B and the enzyme activities involved in C cycling (BG, CBH) decreased physical protection and recalcitrance of SOC. Collectively, our findings demonstrated that the primary mechanism for SOC accumulation in the Helan Mountains was the decrease in aggregate-protected C with an increase in elevation.

Edaphic controls of soil organic carbon in tropical agricultural landscapes

Predicting soil organic carbon (SOC) is problematic in tropical soils because mechanisms of SOC (de)stabilization are not resolved. We aimed to identify such storage mechanisms in a tropical soil landscape constrained by 100 years of similar soil inputs and agricultural disturbance under the production of sugarcane, a C4 grass and bioenergy feedstock. We measured soil physicochemical parameters, SOC concentration, and SOC dynamics by soil horizon to one meter to identify soil parameters that can predict SOC outcomes. Applying correlative analyses, linear mixed model (LMM) regression, model selection by AICc, and hierarchical clustering we found that slow moving SOC was related to many soil parameters, while the fastest moving SOC was only related to soil surface charge. Our models explained 78–79%, 51–57%, 7–8% of variance in SOC concentration, slow pool decay, and fast pool decay, respectively. Top SOC predictors were roots, the ratio of organo-complexed iron (Fe) to aluminum (Al), water stable aggregates (WSagg), and cation exchange capacity (CEC). Using hierarchical clustering we also assessed SOC predictors across gradients of depth and rainfall with strong reductions in Roots, SOC, and slow pool decay associated with increasing depth, while increased rainfall was associated with increased Clay and WSagg and reduced CEC in surface soils. Increased negative surface charge, water stable aggregation, organo-Fe complexation, and root inputs were key SOC protection mechanisms despite high soil disturbance. Further development of these relationships is expected to improve understanding of SOC storage mechanisms and outcomes in similar tropical agricultural soils globally.

Appropriate N addition improves soil aggregate stability through AMF and glomalin‐related soil proteins in a semiarid agroecosystem

AbstractSoil aggregation and structural stability play a crucial role in soil organic carbon (SOC) sequestration. However, the underlying mechanisms of arbuscular mycorrhizal fungi (AMF) and glomalin‐related soil protein (GRSP) responses to N addition and their impacts on soil aggregation and organic carbon stability remain unclear. Hence, a 16‐year field N addition experiment on winter wheat (Triticum aestivum L.) was conducted to investigate the effects on the stability of soil structure and SOC fractions via AMF and GRSP. Overall, N addition increased the soil aggregate mean weight diameter (MWD), which exhibited an increase in the proportion of large macroaggregates and a decrease in the proportion of silt‐clay fractions. Appropriate N (180 kg N ha−1) input increased SOC stability and total SOC stock, while excessive N (360 kg N ha−1) input increased labile organic carbon fractions, and active C index and decreased the C stock. The concentrations of SOC, total GRSP (T‐GRSP), and easily extractable GRSP (EE‐GRSP) showed the largest increases in small macroaggregates, and GRSP was significantly correlated with SOC, recalcitrant organic carbon, and MWD (p &lt; 0.05). These results indicated that appropriate N addition promoted AMF to secrete GRSP, which in turn favoured large macroaggregation and enhanced the physical protection of SOC. Meanwhile, the increased GRSP stimulated the accumulation of recalcitrant C, thus improving soil organic carbon stability and carbon sequestration capacity. The study suggested that appropriate N addition (180 kg N ha−1) should be used to improve the carbon sequestration potential of farmland on the Loess Plateau.

Fractions, stability, and influencing factors of soil organic carbon under different land-use in sodic soils

Salt-affected soils have considerable carbon sequestration potential in aboveground biomass and soil organic carbon (SOC). However, organic carbon pool characteristics and the significant important factors affecting the land use of sodic soils have not been clearly elucidated. In this study, 252 samples were collected from 20 typical sodic soil sites across the western Songnen Plain, China. This study investigated the effects of five land-use types, that is, saline wasteland (SWL), degraded grassland (GL), forestland (FL), upland (UL), and paddy fields (PF), on sodic soil SOC fractions and stabilities to find that UL and PF decreased salinity and alkalinity, but increased soil nutrient and water stability aggregate (WSA) contents and stability. Compared with degraded natural land-use types (SWL and GL), FL and croplands (UL and PF) increased the physical protection of SOC and aggregate-associated SOC contents. Furthermore, cropland, especially PF, increased nonlabile organic carbon (NOC) (7.47 g kg−1), labile organic carbon (LOC) (3.79 g kg−1), dissolved organic carbon (DOC) (0.16 g kg−1), and mineralizable organic carbon (MOC) (0.41 g kg−1) fractions. Furthermore, compared with degraded natural lands, PF increased NOC ratios (59.65%) and carbon management index (CMI) (126.1), thus increasing organic carbon content and stability. Structural equation modelling revealed that improvements in soil properties, total nitrogen (TN), WSA, electrical conductivity (EC), and pH were the crucial factors for increasing SOC stock in sodic soils. We concluded that the positive effect that PF had on SOC content and stability were much greater than that of the other land-use types, and that PF was the optimal management practice for increasing SOC sequestration capacity in sodic soils.