Organic Carbon Stability Research Articles

Progress on the Effect of Nitrogen on Transformation of Soil Organic Carbon

Carbon and nitrogen are the essential elements constituting living organisms and are closely coupled during biogeochemical cycles. Due to the atmospheric nitrogen deposition and increased agricultural nitrogen fertilizer input, the effect of nitrogen on the sequestration of soil organic carbon (SOC) is controversial. To facilitate a comprehensive understanding of this issue, the progress of recent studies on the different SOC stabilization mechanisms is reviewed. Based on the differences in the stability and fate mechanisms of particulate organic carbon (POC) and mineral-associated organic carbon (MAOC), nitrogen input can increase POC input and inhibit microbial decomposition of POC by increasing terrestrial biomass, changing the quality of litter and promoting the formation of aggregates. N input reduces the chemical stability of MAOC by altering the chemical bonding of mineral–organic complexes. This study has promising implications for understanding the effect of N on SOC transformation by different stabilization mechanisms to promote soil carbon sequestration.

Mean annual temperature and carbon availability respectively controlled the contributions of bacterial and fungal residues to organic carbon accumulation in topsoil across China's forests

AbstractAimSoil organic carbon (SOC) stabilization has become an important topic in recent years in the context of global climate change. Microbial residues represent a significant component of stabilized SOC pools. However, spatial variations in the contributions of bacterial and fungal residues to SOC and their determinants at a continental scale remain poorly understood. We aimed to evaluate the spatial variations and controls of the contributions of microbial residues to SOC in forest topsoil.LocationNorth–south transect in eastern China.Time period2014.Major taxa studiedForest ecosystems.MethodsA total of 195 surface (0–10 cm) soils were sampled from 28 forest sites across tropical and boreal forests in eastern China from July to August to assess how biotic and abiotic factors govern the geographic patterns of the contributions of soil microbial residues (indicated by amino sugars) to SOC.ResultsFungal residues (30.0%) had a greater average contribution to SOC than bacterial residues (15.5%). The contributions of bacterial (CBR) and total microbial residues (CMR) to SOC showed negative latitudinal patterns and were positively correlated with mean annual temperature (MAT). In contrast, the contribution of fungal residues to SOC (CFR) showed no clear geographic or climatic patterns. On average, the CBR (9.7%), CFR (21.1%) and CMR (30.8%) were lower in boreal forests than in other biome forests. SOC concentration negatively mediated CBR, CFR and CMR. The piecewise structural equation model results showed that MAT was the primary driver of the geographic pattern of CBR, whereas SOC and soil carbon : nitrogen ratio were more directly associated with the CFR. Additionally, plant factors and microbial properties (i.e., microbial biomass and composition) played relatively little roles in regulating CBR, CFR and CMR.Main conclusionsThese findings advance the current knowledge of the different geographic patterns of CBR and CFR regulated by different potential mechanisms in forest ecosystems. This highlights that the dynamics of microbial residues could potentially have unexpected consequences for topsoil SOC stocks under climate change.

Geochemistry of the Cretaceous Mowry Shale in the Wind River Basin, Wyoming

The siliceous nature of the Mowry Shale distinguishes it from many of the well-studied organic-rich mudstones of the Cretaceous Western Interior Seaway. Available models of organic enrichment in mudstones rarely incorporate detailed biomarker, bulk organic, inorganic, and mineralogy data. Here, we used these data to evaluate how variations in organic matter source, productivity, dilution, and preservation modulated organic matter accumulation during the deposition of the Mowry Shale, while also demonstrating the benefits of this integrated approach. An organic stable carbon isotope vertical profile for the Mowry Shale is presented to test whether the Mowry Shale was deposited during oceanic anoxic event 1d (OAE 1d), thereby contributing to organic enrichment in the Mowry Shale. Samples were analyzed from three thermally immature drill cores collected from the Wind River Basin, Wyoming to advance our understanding of the conditions that led to the formation of the Mowry Shale. Results from bulk organic and inorganic geochemistry and biomarkers show that redox-driven preservation is closely coupled with stratigraphic changes in organic matter content in intermediate to distal settings of the Mowry Shale. Biogenic silica dilution decouples productivity and organic enrichment, such that the interval that was deposited during the highest productivity is offset from the interval containing maximum organic content. These findings contrast with previous studies that identified productivity as the primary driver of organic enrichment in distal settings of the Mowry Shale. The middle and lower Mowry Shale contain primarily marine organic matter, whereas the relative contribution of terrestrial organic matter increases in the upper Mowry Shale and overlying Frontier Formation as relative sea level declined and the western shoreline prograded eastward. Finally, the organic stable carbon isotope profile of the Mowry Shale together with recent radioisotopic dating suggest that the Mowry Shale postdates OAE 1d by ∼1−2 million years (m.y.), providing another example of temporal offset between organic matter accumulation in the Cretaceous Western Interior Seaway compared to other regions that record global OAEs.

Distribution of Organic Carbon Fractions in Soil Aggregates and Their Contribution to Soil Aggregate Formation of Paddy Soils

ABSTRACT Different soil organic matter fractions play different roles in governing soil aggregation. Therefore, this study determined the distribution of labile organic carbon (OC) and stable OC fractions in soil aggregates and their contribution to the soil aggregation of paddy soils in the Central Plain of Thailand. Quantitative analysis of the OC fractions in soil aggregates was determined using wet oxidation method and their changes in the chemical composition of organic compounds were investigated using FTIR spectroscopy. The results showed that the large macroaggregate (LMA: 2–8 mm) content of studied soils generally increased with increasing soil organic carbon, clay, polyvalent cations and aluminum (Al) oxides contents. Generally, both the labile OC and stable OC fractions increased with increasing aggregate size classes, suggesting a hierarchical order of soil aggregation and physical protection of organic matter against microbial decomposition. The labile OC fraction in all aggregate size classes was positively correlated with the content of LMA (r = 0.54*–0.77**), suggesting that the labile OC fraction represented a major organic cementing agent that contributed to LMA formation. FTIR analysis revealed that the labile OC fraction mainly consisted of plant-derived and microbial-derived polysaccharides. Therefore, paddy soils with higher organic cementing agent (labile OC fraction) and inorganic cementing/flocculating agents may provide a stronger intimate association of these transient binding agents, particularly the microbial-derived polysaccharides with clay mineral surfaces and metal cations/Al oxides. In turn, the greater amounts of stabilized, microbial-derived polysaccharides also efficiently promoted the formation of LMA from a combination of microaggregates.

Size matters: biochemical mineralization and microbial incorporation of dicarboxylic acids in soil

The transformation and turnover time of medium- to long-chain dicarboxylic acids (DCA) in soil is regulated by microbial uptake and mineralization. However, the chain length of n-alkyl lipids may have a remarkable influence on its microbial utilization and mineralization and therefore on the formation of stable soil organic carbon from e.g. leave- needle- and root-derived organic matter during decomposition. To investigate their size dependent mineralization and microbial incorporation, four DCA of different chain lengths (12–30 carbon atoms), that were 13C labeled at each of their terminal carboxylic groups, were applied to the Ah horizon of a Fluvic Gleysol. Incorporation of 13C into CO2 and in distinct microbial groups classified by phospholipid fatty acid (PLFA) analysis was investigated. Mineralization of DCA and incorporation into PLFA decreased with increasing chain length, and the mineralization rate was highest during the first days of incubation. Half-life time of DCA carbon in soil increased from 7.6 days for C12 DCA to 86.6 days for C18 DCA and decreased again to 46.2 days for C22 DCA, whereas C30 DCA had the longest half-life time. Rapid and efficient uptake of C12 DCA as an intact molecule was observable. Gram-negative bacteria incorporated higher amounts of DCA-derived 13C compared to other microbial groups, especially compared to actinomycetes and fungi during the first phase of incubation. However, the incorporation of C12 DCA derived 13C into the PLFA of actinomycetes, and fungi increased steadily during the entire incubation time, suggesting that those groups take up the 13C label from necromass of bacteria that used the C12 DCA for formation of their lipids before.

Effects of exogenous organic/inorganic nitrogen addition on carbon pool distribution and transformation in grassland soil

AimsIncreases in nitrogen (N) deposition may significantly affect the organic carbon (OC) cycle in soil. The inconsistent findings of the influence of added N on soil OC pools highlight the need of quantifying responses of the OC pool distribution to N addition. Moreover, the influence of N addition with a mixture of organic and inorganic N on OC pool distribution and stabilization in grassland soil remains unclear. MethodsWe carried out a five-year field experiment with adding N to examine the effects of different types of N addition on soil OC pool distribution and transformation in a meadow steppe in Inner Mongolia. We applied N in the ratios of inorganic N (IN) and organic N (ON) at 10:0 (N1), 7:3 (N2), 5:5 (N3), 3:7 (N4), 0:10 (N5), and 0:0 (CK), respectively. We measured OC content in bulk soil, particulate organic matter (POM), and mineral-associated organic matter (MAOM) fractions. Additionally, a short-term soil incubation was conducted to assess potential OC mineralization. ResultsOur study showed no significant effect on soil organic carbon content of different ratios of IN/ON addition. N addition reduced microbial biomass C/N ratio, the fraction of mineral-associated organic matter, cumulative CO2 emission, and microbial metabolic quotient. Compared with ON addition alone, IN addition alone showed a stronger effect on the C in different soil fractions and soil OC mineralization. The particulate organic matter (POM) fraction was more sensitive to N addition than the mineral-associated organic matter (MAOM) fraction. ConclusionsOur results suggest that the contribution of N in organic and inorganic forms affecting OC pool distribution with different turnover rates should be considered when assessing the effects of N addition types on soil OC processes in grassland.

Particulate and mineral-associated organic carbon fractions reveal the roles of soil aggregates under different land-use types in a karst faulted basin of China

Soil aggregation has been recognized as the main mechanism of organic carbon (C; OC) stabilization, and OC dynamics within aggregates are closely linked to soil OC (SOC) sequestration. To unravel the roles of different-sized aggregates and the associated OC fractions in SOC accumulation, SOC stocks (SOCS), aggregate distributions, and OC fractions within aggregates were measured under five typical land-use types (cropland, grassland, shrubland, plantation forest, and natural forest) in a karst faulted basin, China. Land-use type had distinct effects on SOCS in the topsoil (0–10 cm) and along the soil profile (0–60 cm), and the primary factors influencing SOCS varied with the soil horizons. Plantation forest had the highest SOCS (51.2 Mg C ha−1) in the topsoil, whereas the SOCS in shrubland (182.7 Mg C ha−1) was distinctively higher than those of other land-use types across the soil profile. Soil microbial biomass C and mean weight diameter were the major factors driving SOCS variation in the topsoil layer and the entire soil profile, respectively. OC content within macroaggregates (>0.25 mm) was significantly positively correlated with the SOC content of bulk soil, whereas only the mass proportion of large macroaggregates (>2 mm) showed a positive relationship with SOC. Additionally, mineral-associated OC (MAOC) was the dominant fraction of SOC and was abundant in macroaggregates. However, particulate OC (POC) within aggregates was relatively enriched in the topsoil and microaggregates. Considering the decomposition and distribution characteristics of OC fractions in different-sized aggregates, we suggest that the POC/MAOC ratios of macro- and microaggregates could respectively reflect aggregate capacity to sequestrate MAOC and POC across different land-use types. Overall, shrubland is the optimal land-use type for rocky desertification control in the karst fault basin, due to the protection of POC and MAOC within different-sized aggregates.

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 < 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.

Soil organic carbon stabilization and associated mineral protection in typical coastal wetlands under different hydrologic conditions

The soil carbon sequestration largely depends on soil organic carbon (SOC) stability. However, the mechanism of SOC stabilization in coastal wetlands under different hydrologic conditions remains to be clarified. In this study, the effect of mineral protection on SOC stabilization was investigated in freshwater-flooded Phragmites australis wetlands (FPW), tidal P. australis wetlands (TPW), non-flooded P. australis wetlands (NPW) and tidal Suaeda salsa wetlands (TSW). Two stabilized SOC fractions (Na2S2O8 resistant SOC and H2O2 resistant SOC) and Al/Fe/Si oxides extracted by acid oxalate, dithionite–citrate and pyrophosphate, respectively, were determined in soil samples collected to a depth of 25 cm. The contents of soil Na2S2O8 resistant SOC and H2O2 resistant SOC were not significantly different among the four wetlands (p > 0.05), with the highest mean values occurring in FPW (1.44 ± 0.43 g kg-1) and TPW (1.79 ± 0.40 g kg-1), respectively. The contents of Al/Fe/Si oxides (except for Sip) and the values of mineral phase indicators were significantly lower in NPW than in TPW or FPW (p < 0.05). Linear regressions among Al/Fe/Si oxides, mineral phase indicators, and two stabilized SOC fractions showed that Na2S2O8 resistant SOC and H2O2 resistant SOC were positively and significantly affected by mineral contents (p < 0.05). Additionally, edaphic factors such as soil organic matter, total nitrogen, soil water content, clay and silt contents were identified as important factors influencing the two stabilized SOC fractions.

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.

Importance of soil labile organic carbon fractions in shaping microbial community after vegetation restoration

Studies have been increasingly focusing on soil carbon (C) pools to facilitate the sequestration and stabilisation of soil organic carbon (SOC). However, interactions between different SOC fractions and microbial communities have remained largely unexplored after vegetation restoration on the Loess Plateau. To address this gap, we analysed 16S and ITS rRNA gene sequencing, active SOC (Ca), slow SOC (Cs), passive SOC (Cp) and edaphic factors to decipher the importance of soil C fractions in shaping microbial communities after vegetation restoration. Compared to CK (Control, cropland), the average of SOC contents improved 70.52 % (p < 0.05), and the Ca, Cs and Cp improved 83.18 % (p < 0.05), 128.74 % (p < 0.05) and 18.69 % (p > 0.05). Under different land use types, the relative abundance of four bacterial phyla and two fungal phylum were > 80 % and 75 %, respectively. The Actinobacteria relative abundance in natural grassland and natural shrubland was higher than that in CK. The Shannon index, Chao index and OTUs of soil fungal and bacterial communities under CK were significantly lower than that of other land use types, except for artificial grassland (p < 0.05). The microbial communities transited from oligotrophic to copiotrophic groups according to the results of redundancy analysis (RDA), and the cumulative loads of two axes of RDA in bacterial and fungal communities approached 89.90 % and 88.19 %. The variation partitioning analysis showed that Ca and Cs exhibited large path coefficients in explaining the changes in soil microbial communities. And the microbial communities were mediated through change in labile organic C according to structural equation models, indicating that the structures and compositions of microbial communities were mainly under the control of labile SOC content after vegetation restoration. These results are referentially valuable for comprehending how to apply labile SOC in predicting variations of microbial communities and improving predictive ecosystem models for early-warning indicators of soil degradation.

Long-term partial substitution of chemical nitrogen fertilizer with organic fertilizers increased SOC stability by mediating soil C mineralization and enzyme activities in a rubber plantation of Hainan Island, China

The partial substitution of chemical nitrogen (N) fertilizer with organic fertilizers is widely used to maintain soil fertility and enhance crop yield, although its effects on soil organic carbon (SOC) composition, mineralization and stability are not fully understood. For this study, a 12-year field experiment was conducted in a rubber plantation field of Hainan Island, China. Three fertilizer treatments included no fertilizer application as control (CK), chemical fertilizer application (NPK), and half of the chemical N fertilizer plus manure application equivalent to half of chemical N fertilizer (NPKM). We determined the soil physicochemical properties, four labile SOC compositions (microbial biomass carbon (MBC), light fraction organic carbon (LFOC), dissolved organic carbon, dissolved organic carbon extracted by hot water (HOC), particulate organic carbon (POC)), four C-associated soil enzymes (β-1, 4-glucosidase (BG), polyphenol oxidase (POX), catalase (CAT) and cellulase), and SOC mineralization (from a 46-day aerobic incubation experiment) in two soil layers (topsoil layer (0–10 cm) and subsoil layer (10–20 cm)). Compared with NPK, NPKM significantly increased soil pH, total nitrogen, total phosphorus, available phosphorus and potassium, NH4+-N, and NO3−-N contents, and SOC, LFOC, POC, HOC, and MBC concentrations. NPKM had higher cumulative CO2 production but lower SOC mineralization potential (Cp) than NPK, although the difference was not significant. In both soil layers, NPKM significantly increased POX activity, but decreased BG and CAT activities. Soil pH can regulate enzyme activities and synthesis in acidic soil in a tropical region with a significantly positive correlation with POX activity. Compared with NPK, the relatively lower Cp/SOC and higher carbon quality index (CQI) indicated higher SOC stability (Cp/SOC) in NPKM. The redundancy analysis results revealed that the dominant factors affecting SOC stability were NH4+-N, pH, POC and MBC in NPK, and available phosphorus, BG, and pH in NPKM. In the three fertilization treatments, the POX was the dominant factor affecting the CQI. Conclusively, half of the chemical N fertilizer plus half of the manure application could facilitate SOC stability by mediating soil C mineralization and enzyme activities in the rubber plantation of Hainan Island, China.

A novel two-stage process for the effective treatment of swine wastewater using Chlorella sorokiniana AK-1 based algal-bacterial consortium under semi-continuous operation

This study aimed at developing an eco-friendly and effective treatment for swine wastewater (SWW) using a designer microalgae-bacteria consortium. A functional algal bacterial consortium was developed with SWW-derived bacteria and Chlorella sorokiniana AK-1. Light intensity (300 µmol/m2/s) and inoculum size (0.15 and 0.2 g/L for microalgae and bacteria) were optimized. Semi-batch operation treating 50 % SWW resulted in a COD, BOD, TN, and TP removal efficiency of 81.1 ± 0.9 %, 97.0 ± 0.7 %, 90.6 ± 1.6 % and 91.3 ± 1.1 %, respectively. A novel two-stage process with an initial bacterial start-up stage followed by microalgal inoculation was applied for attaining stable organic carbon removal, in addition to satisfactory TN and TP removal. Full strength SWW was treated with this strategy with COD, BOD, TN, and TP removal efficiencies of 72.1 %, 94.9 %, 88 %, and 94.6 %, respectively. The biomass consisted of 36 % carbohydrates, indicating a potential feedstock for biochar production. In addition, the effluent met the standards for effluent discharge in Taiwan.

Nano and sub-nano scale distribution of organic carbon species on soil particles revealed by Cs-STEM EELS

Understanding the heterogeneous distribution of soil organic matter (SOM) on soil particles is essential for predicting the stability of organic carbon (C) in soil, but direct visualization of the microscopic distribution of organic C in soil is still challenging due to the complexity of soil particles. In this study, a paddy soil was fractionated and spherical aberration corrected scanning transmission electron microscopy (Cs-STEM) coupled with electron energy loss spectroscopy (EELS) was employed to analyze the microscopic distribution of organic C species on clay-sized soil particles (<2000 nm) from the different size fractions (800–2000 nm, 100–800 nm and 0–100 nm) at the nano and sub-nano scale. The EELS results demonstrated that the relative abundance of both phenolic and aliphatic C was quite independent of the particle size fractions, while aromatic and carboxyl carbon demonstrated the largest variations between fractions. With the decrease in soil particle size from 800 to 2000 nm to 0–100 nm, the median abundance of carboxyl (oxidized) C increased from 23% to 35%, and aromatic (reduced) C decreased accordingly from 40% to 16%. The statistical analysis demonstrated that the local organic C concentration was the major factor accounting for the variations in oxidized and reduced C species in soil particles, in which selective sorption of the organic C abundant of acidic functional groups by reactive minerals was responsible for the enrichment of oxidized C in small clay size soil particles. Overall, the results of this study contribute to an improved understanding of the chemical diversity of SOM in organo-mineral interfaces and provide insights in the microscopic C stabilization mechanisms in natural soils.

Characteristics of Soil Organic Carbon Fractions and Stability along a Chronosequence of Cryptomeria japonica var. sinensis Plantation in the Rainy Area of Western China

Soil organic carbon (SOC) is critical for carbon cycling and sequestration in forest ecosystems. However, how stand age affects SOC components and stability still remains poorly understood. Here, soil samples (0–20 cm) were collected from Cryptomeria japonica var. sinensis (L. f.) D. Don plantations of seven stand ages (6, 12, 23, 27, 32, 46, 52 a) in the rainy area of western China. SOC fractions, including soil particulate organic carbon (POC), easily oxidizable carbon (EOC), labile organic carbon (LOC), recalcitrant organic carbon (ROC), and light fraction organic carbon (LFOC), were determined to explore the nature of carbon components and stability across a chronosequence of C. japonica plantation. Soil carbon fractions first increased and then trended to be stable with an increase in stand age. SOC concentrations were the largest in mature forests (27 or 32 a), but the concentrations of other carbon components often peaked in early over-mature forests (46 a). The concentrations of all carbon fractions were the lowest in the young forests (6 a). The ratios of ROC/SOC increased and LOC/SOC decreased with increasing stand age. Almost all carbon fractions were positively correlated with soil bulk density and negatively correlated with soil moisture. The allometric exponent of ROC or HFOC and soil physicochemical properties was higher as compared to LOC and LFOC. The results noted in this study indicate that SOC components often accumulate fast over the first 20 years of afforestation and SOC stability increases with increasing stand age for C. japonica plantation in this specific region.

Effect of Antibiotic-Degrading Bacteria on Maturity and Bacterial Community Succession During Pig Manure Composting

The inoculation of antibiotic-degrading bacteria into manure could promote the removal of antibiotics during composting. However, knowledge on the impact of inoculating these antibiotic-degrading bacteria on the composting process and indigenous microbial community succession is still limited. This study assessed the antibiotic removal efficiency in pig manure after inoculating a microbial inoculum with antibiotic-degrading bacteria as the key component. The effect of inoculating this microbial inoculum on the physicochemical dynamics and the succession of the manure bacterial community during composting was also analyzed. The results showed that the antibiotic degradation in pig manure reached 81.95% after inoculating the microbial inoculum. When compared with that in the control, the total concentration of antibiotic residues in manure with the microbial agent inoculated was decreased by 42.18%. During composting, inoculating the microbial inoculum accelerated the temperature rise of compost, favored water loss, and alleviated the release of NH3 and H2S. Moreover, the total nutrient content (nitrogen, phosphorus, and potassium) in the final compost and the germination index of radish seeds increased by 6.80% and 68.33%, respectively, after inoculating this microbial inoculum. Furthermore, inoculating the microbial inoculum increased the content of stable organic carbon in the final compost and decreased the content of recalcitrant substances such as cellulose and hemicellulose. The analysis of the manure bacterial community showed that inoculating the microbial inoculum increased the relative abundances of Actinomycetes and Firmicutes in the compost. In particular, the thermophilic bacteria that was positively related to the compost temperature was increased significantly (P<0.01) after inoculating the microbial inoculum, whereas the relative abundance of pathogenic bacteria was correspondingly decreased. Network analysis of the bacterial coexistence pattern showed that inoculating this microbial inoculum also changed the interaction pattern of indigenous manure bacterial communities, which greatly reduced the complexity and connectivity of the bacterial interaction and improved the ecological relationship between beneficial bacteria and other bacterial communities. The effect of this microbial inoculum on the interaction with manure bacterial community laid a foundation for the establishment of a new and healthier composting bacterial community. This study provides a scientific basis for the application and development of multifunctional antibiotic-degrading microbial agents in manure treatments.

Characteristics of Soil Organic Carbon Components and Their Correlation with Other Soil Physical and Chemical Factors in Cotton Fields with Different Continuous Cropping Years in the Oasis on the Northern Edge of Tarim Basin

The study of soil organic carbon components in continuous cropping cotton fields in oases is helpful to reveal the change characteristics of the soil organic carbon stability mechanism in arid areas under the effects of man-land relationships. In this study, the contents of soil organic carbon, easily oxidized organic carbon, dissolved organic carbon, and microbial biomass carbon in cotton fields with different continuous cropping years (2 a, 5 a, 12 a, 20 a, and 35 a) were collected and analyzed by using space instead of the time series method. Through redundancy analysis, the relationship between soil organic carbon components and other soil physical and chemical factors was discussed. The results showed that:① continuous cropping for different years had a significant impact on the content of soil organic carbon components in the study area. The contents of soil organic carbon, easily oxidized organic carbon, dissolved organic carbon, and microbial biomass carbon in continuous cropping cotton fields for 12 a, 20 a, and 35 a were higher than those in continuous cropping cotton fields and wasteland for 2 a and 5 a. ω(soil organic carbon) reached the peak value (7.06 g·kg-1) in the cotton field in 20 a, which was 76.91% higher than that in the wasteland. The content of soil organic carbon decreased with the deepening of the soil layer. ② Based on the redundancy analysis of soil organic carbon content and soil environmental factors, the results showed that the content of soil organic carbon was positively correlated with total nitrogen, available phosphorus, and water content and negatively correlated with pH value and bulk density. The importance of soil environmental factors on the interpretation of soil organic carbon content was as follows:total N>available P>pH value>bulk density>water content>available K>total salt.

Biogeochemical appraisal of carbon fractions and carbon stock in riparian soils of the Ganga River basin

The farmers are approaching river/reservoir beds to produce crops and vegetables during the lean periods, especially post-monsoon, winter, and summer, for their livelihood in changing climatic scenarios. Comparing C fractions, C stocks, and microbial indices between the terrestrial (conventional agricultural land: CAL) and riparian zones (reservoir riparian zones: RSRZ and river riparian zones: RRZ) reveals that cultivating riparian zones is environmentally stressful and climatically vulnerable to livelihood practices. The moist riverbed conditions for cultivation result in the accumulation of residual biomass and the burial of soil organic matter. The C fractions showed decreasing trends as CAL > RSRZ > RRZ. The mean TOC stock was found high in the CAL soils (45.04 Mg C ha−1) than in the RRZ (40.65 Mg C ha−1) and RSRZ soils (38.01 Mg C ha−1). The labile C fraction (KMnO4-C) varied from 2.34 to 3.29 % of TOC, and the RSRZ and RRZ soils showed 14.50 % and 40.32 % less KMnO4-C than the CAL soils. The relationship between KMnO4-C and mineralizable C (Cmin) showed high potential for organic carbon stabilization in riparian soils. The microbial biomass carbon (MBC) and basal soil respiration (BSR) values were nearly half of the CAL in the RRZ soils indicating limited carbon substrate availability to the microbial decomposition. Low mineralization quotient (qM) and high metabolic quotient (qCO2) indicated stressful microbial utilization of labile TOC in the RRZ soils. The high carbon management index (CMI) showed the potential to store and sequester TOC in riparian soils. The artificial neural networks (ANN) were used to examine the impact of soil properties on the prediction efficiency of TOC stocks in the three farming zones.

The effects of co-utilizing green manure and rice straw on soil aggregates and soil carbon stability in a paddy soil in southern China

The co-utilization of green manure (GM) and rice straw (RS) in paddy fields has been widely applied as an effective practice in southern China. However, its effects on soil aggregate and soil organic carbon (SOC) stability remain unclear. In the present study, the effect of GM, RS, and co-utilization of GM and RS on particle size distribution of soil aggregates and SOC density fractions were measured in a field experiment. The experiment included six treatments, i.e., winter fallow (WF) without RS return (Ctrl), WF with 50% RS return (1/2RS), WF with 100% RS return (RS), GM without RS return (GM), GM with 50% RS return (GM1/2RS) and GM with 100% RS return (GMRS). The results showed that the proportion of small macro-aggregates (0.25–2 mm) and the mean weight diameter (MWD) of aggregates in the GMRS treatment was greater (by 18.9 and 3.41%, respectively) than in the RS treatment, while the proportion of silt+clay particles (<0.053 mm) was lower (by 14.4%). The concentration of SOC in microaggregates (0.053–0.25 mm) and silt+clay particles was higher in the GMRS treatment than in GM and RS treatments individually. The concentration and proportion of free light organic carbon (fLOC) in aggregates of various particle sizes and bulk soil was greater in the GMRS treatment than the RS treatment, whereas the concentration and proportion of mineral-associated organic carbon in small macroaggregates, microaggregates, and bulk was lower in the GMRS treatment than in the RS treatment. The proportion of intra-aggregate particulate organic carbon (iPOC) was greater in the GMRS treatment than in GM treatment. The GMRS treatment had strong positive effects on iPOC in small macroaggregates, suggesting that SOC was transferred from fLOC to iPOC. In conclusion, co-utilizing green manure and rice straw cultivated the SOC pool by increasing the concentration of fLOC and improved soil carbon stability by promoting the sequestration of organic carbon in iPOC as a form of physical protection.

Influence of Organic Amendments on Soil Carbon Sequestration Potential of Paddy Soils under Two Irrigation Regimes

Soil organic carbon (OC) is one of the most important soil components regulating soil quality, fertility and agronomic productivity as well as the global carbon (C) cycle. Soil acts as a sink for global C, which can be influenced by the water regime and organic matter (OM) management in field. The aim of this study is to evaluate the effect of the application of different organic amendments on C sequestration in paddy soils under contrasting irrigation regimes. A 4-month pot experiment was conducted under net house conditions and the treatments were composed of two organic amendments: rice straw (RS) and poultry manure (PM); four application rates of amendment: 0 g (control), 2.5 g, 5.0 g and 15.0 g kg−1 soil; and two irrigation regimes: (i) continuous waterlogging condition (CWL) and (ii) alternate wetting and drying (AWD). After the incubation period, soil samples were collected from the pot and isolated into labile (&gt;53 µm) and mineral-associated (&lt;53 µm) OM. Bulk (before and after incubation) and fractionated soil samples were analyzed for OC, total nitrogen (N), C:N ratio; and C sequestration percentage was calculated. Relatively higher amounts of soil OC were present in CWL condition (1.23%) than AWD (1.13%). The C sequestration potential also showed the similar trend (CWL: 47% &gt; AWD: 35%). This was explained by the induced aerobic condition in between the anerobic condition in AWD and the continuous anaerobic condition in CWL which resulted in a difference in OM decomposition. The mineral-associated OM fraction (&lt;53 µm) was higher in the CWL condition than AWD condition which also indicated the importance of the chemical stabilization of OC (OC bound to minerals) in the CWL condition. The application of PM led to a significant increase (45%) in C sequestration potential than RS (37%). This could be attributed to C:N ratio and probable biochemical composition of amendments which resulted in lower decomposability of PM than RS, and also in line with the higher distribution of OC in mineral-bound OM than labile fraction. The application of higher organic amendments did not increase OC content, and declined C sequestration potential in soils as the microbial activity presumably did not match with the amendment amount. Overall, C sequestration potential was higher with 5 g PM kg−1 soil application under CWL-irrigated paddy soil. The findings indicated the need to pay more attention to the selection of the proper type and rate of organic amendments for higher C sequestration in soil under a specific irrigation system for sustainable agriculture.