Carbon Mineralization Potential Research Articles

Technology to Increase Carbon Mineralization Potential of Crop Residues under Cotton-Maize-Pulse Cropping System

Background: Cotton, maize and pulses are widely grown crops in the western zone of Tamil Nadu, resulting in a significant accumulation of crop residues throughout the year. The persistence of these crop residues after harvest can cause problems for farmers and the soil system. Therefore, the goal of the current study is to investigate the carbon mineralization process in these residues to enrich the soil’s nutrient content, turning waste into a valuable resource. Methods: The incubation experiment comprised 13 treatments, each with three replicates. These included a control, surface residue addition, buried residue addition and various combinations of soil, residue, microbial consortia, urea and jaggery, both on the soil surface (S) and incorporated into the soil (I). Result: The incorporation of crop residues into the soil, along with the addition of 1% microbial consortia, 2.0% jaggery and 1% urea, significantly enhanced carbon mineralization. Among the three crop residues, cowpea exhibited the highest performance, followed by cotton and maize, with values of 692, 564 and 522 µg C g-1 soil, respectively. This trend was further supported by the Michaelis-Menten model (V = 951.72 * x/22.13 + x), with a high goodness-of-fit represented by an R2 value of 0.95 for cowpea. The maximum Vmax (951.72 µmol/min) further substantiates the efficient carbon mineralization achieved by utilizing allocated resources in cowpea-incorporated crop residues (CWFI).

Long-term agro-management strategies shape soil bacterial community structure in dryland wheat systems

Soil microbes play a crucial role in soil organic matter decomposition and nutrient cycling and are influenced by management practices. Therefore, quantifying the impacts of various agricultural management practices on soil microbiomes and their activity is crucial for making informed management decisions. This study aimed to assess the impact of various management systems on soil bacterial abundance and diversity, soil enzyme activities and carbon mineralization potential in wheat-based systems. To accomplish this, soil samples from 0 to 15 cm depth were collected from ongoing long-term field trials in eastern Oregon region under wheat (Triticum aestivum L.)-fallow (WF), WF with different tillage (WT), wheat-pea (Pisum sativum L.) (WP), WF under different crop residue management (CR) and natural undisturbed/unmanaged grassland pasture (GP). These trials consisted of an array of treatments like tillage intensities, nitrogen rates, organic amendments, and seasonal residue burning. This study was a part of the Soil Health Institute’s North American Project to Evaluate Soil Health measurements (NAPESHM). Bacterial community structure was determined using amplicon sequencing of the V4 region of 16SrRNA genes and followed the protocols of the Earth Microbiome Project. In addition, extracellular enzyme activities, and carbon mineralization potential (1d-CO2) were measured. Among different trials, 1d-CO2 in WT, WP, and CR studies averaged 53%, 51% and 87% lower than GP systems, respectively. Enzyme activities were significantly greater in GP compared to the other managements and followed similar trend as respiration. We observed higher evenness in GP and higher richness in spring residue burning treatment of CR study. Our results indicated that species evenness is perhaps a better indicator of soil health in comparison to other indices in dryland wheat systems.

Carbon and Nitrogen Mineralization Kinetics in Soil Under Differential Nutrient Management Regimes in Inceptisols of Coastal India

ABSTRACT In intensive cropping systems, nutrient, and residue management techniques have a tendency to change the soil’s carbon (C) and nitrogen (N) cycle and, consequently, its potential for sequestration and loss. To understand the carbon and nitrogen mineralization kinetics, laboratory incubation studies were conducted with soils at variable depths from a long-term nutrient management experiment on cereal-vegetable-pulse cropping system. The experiment was laid out completely randomized design with 10 treatments replicated thrice. Long-term integrated application of inorganics with organics, biofertilizers, and amendment along with crop residues showed higher carbon and nitrogen mineralization potential and lower potential was observed in soils where crops were raised without application of any nutrient inputs (control) and uncultivated fallow. It was calculated that the potential for higher levels of carbon and nitrogen mineralization existed in the surface (0–15 cm) and subsurface (15–30 cm) layers, respectively, and was negligible in the deeper layer (30–45 cm). The mineralization rate was initially faster up to 42 days of incubation, indicating proper utilization of readily decomposable soil organic matter in the labile pools and thereafter found to slow down. Addition of lime along with the integrated use of organics and inorganics has found to raise the pH to a level that provides a suitable soil environment which affects the carbon and nitrogen mineralization kinetics resulting in buildup of total organic carbon and total nitrogen in the soils. The first-order kinetic model was the best fit in explaining the kinetic parameters of C and N mineralization. Soils under integrated nutrient management (INM) with farmyard manure (FYM) along with biofertilizers, amendment, and inorganic nutrients exhibited better carbon dynamics higher C mineralization (Cmin), potentially mineralizable C (C0), rate of C mineralization (dCmin/dt), and C mineralization quotient (qM), whereas soils applied with similar combinations with vermicompost was found effective for better nitrogen dynamics in terms of enhanced N mineralization (Nmin), potentially mineralizable N (N0), rate of N mineralization (dNmin/dt) and active N fraction over control and fallow soils. Integrated application of inorganic and organic inputs with crop residues over the years has shown beneficial impacts on soil carbon and nitrogen mineralization processes and their kinetics.

Potential carbon mineralization assays are confounded by different soil drying temperatures

Measuring carbon dioxide (CO2) produced after re-wetting previously dried soil is an increasingly popular soil health assay, but there is disagreement on the optimal soil drying temperature. We tested whether soil drying temperature impacts water-extractable organic carbon (WEOC) and soil CO2 emissions following rewetting. Soils were collected from corn/soybean croplands and adjacent perennial vegetation at four sites in Iowa, USA. Soil replicates were dried at 22 °C, 35 °C, 55 °C, 85 °C, and rewetted for incubation at 22 °C. Soil WEOC and CO2 emissions after re-wetting increased nonlinearly with drying temperature. Effects on CO2 were largest after four days of incubation, but cumulative differences persisted even after 42 days. Responses of CO2 and its stable isotope ratio (δ13C) to increased drying temperature varied among sites and vegetation types, indicating shifts in C sources. Soil health assays performed with different soil drying temperatures may not be directly comparable, effects of drying temperature may vary idiosyncratically among samples, and drying at 22 °C or 35 °C as opposed to higher temperatures may be preferable to avoid increasing C availability.

Linking soil phosphorus fractions to associated microbial functional profiles under crop rotation on the Loess Plateau of China

Crop rotation plays an essential role in maintaining soil fertility and is meaningful to soil health and sustainable agricultural management. However, the impact of crop rotational regimes on the soil phosphorus (P) fractions and associated phosphorus cycling (P-cycling) profiles driven by microbial communities are not well elucidated. Hence, we used metagenomics to comprehensively investigate the variations in soil microbial P-cycling functional genes and representative processes, as well their regulations for soil P fractions among distinct crop rotational regimes and complexity. Most soil properties, particularly P fractions, were significantly greater in corn rotations than other crop rotations. The composition of P-cycling functional genes and microbial communities was also distinctly clustered in accordance with crop rotational regimes to varying degrees. The potential of representative P-cycling processes was all significantly higher in the complex rotation. Notably, the key functional genes including phoD, ppx, pstB, ugpA were differently screened from each P-cycling process and assembled toward the middle of their networks. Furthermore, soil potential carbon mineralization as a dominant property regulated several P-cycling processes and was intimately associated with the key P-cycling functional genes. Crop rotational complexity and the P-uptake and transport process had profoundly total effects on soil P fractions. Overall, this study provides a deep insight into soil microbial P-cycling functional profiles for developing sustainable soil P management practices at crop rotational agroecosystems.

Maximizing soil organic carbon stocks under cover cropping: insights from long-term agricultural experiments in North America

Cover crops are widely advocated for increasing soil organic carbon (SOC) levels, thereby benefiting soil health improvement and climate change mitigation. Few regional-scale studies have robustly explored SOC stocks under cover cropping, due to limited long-term experiments. We used the unique experimental data from the North American Project to Evaluate Soil Health Measurements conducted in 2019 to address this issue. This study included 19 agricultural research sites with 36 pairs of cover cropping established between 1896 and 2014. Explanatory variables related to site-specific environmental conditions and management practices were collected to identify and prioritize contributing factors that affect SOC stocks with cover crops, by coupling the Boruta algorithm and structural equation modeling. Overall, cover crops significantly (P < 0.05) improved several indicators of soil health, including greater SOC (concentration: +8%; stock: +7%), total nitrogen (+8%), water-stable aggregates (+15%), and potential carbon mineralization (+34%), on average, compared to no cover crop control. Likewise, on average, cover crops sequestered SOC 3.55 Mg C ha-1 (0–15 cm depth), with a sequestration rate of 0.24 Mg C ha-1 yr-1. In addition, we found climate (Hargreaves climatic moisture deficit) was important in explaining the variation of SOC stocks with cover crops, followed by soil properties (e.g., soil clay content). In terms of management practices, cover crop type had a significant positive (0.36) effect on SOC stocks, with non-legumes showing a greater impact, compared to legumes and mixtures. Crop rotational diversity also had a positive (0.28) effect on SOC accumulation. Our findings suggested that integrating non-legume cover crops into diverse crop rotation is likely to be a promising strategy to maximize SOC stocks with cover crops across North America.

Differential Responses of Soil Microbial N-Cycling Functional Genes to 35 yr Applications of Chemical Fertilizer and Organic Manure in Wheat Field Soil on Loess Plateau

Fertilization changes nitrogen (N)-cycling processes and associated microbial communities in agricultural ecosystems. However, the long-term responses of N-cycling potential and microbial functional genes to different fertilization sources remain unclear. Soil samples were collected to a depth of 20 cm under winter wheat applied annually with N fertilizer (NF), organic manure (OM), N fertilizer plus organic manure (NM), and a control without fertilization (CK) for 35 yr, and they were analyzed for microbial functional genes involved in soil N cycling using metagenome sequencing in the Loess Plateau of China. Soil N fractions were greater with OM and NM than NF and CK. The total abundances of N-cycling genes were 9.3% (p &lt; 0.05) greater with NM than CK, and 8.2% (p &lt; 0.05) and 12.2% (p &lt; 0.01) higher with OM and NM than NF, respectively. Compared to CK, OM and NM increased the abundance of genes associated with nitrification, denitrification, dissimilatory nitrate reduction, and assimilatory nitrate reduction, but decreased the abundance of genes related to organic N metabolism. However, NF increased the abundance of genes involved in nitrification. Both OM and NM also enhanced the relative abundance of Proteobacteria carrying N-cycling genes but reduced those of Firmicutes and Cyanobacteria. Soil organic carbon, total N, and potential carbon mineralization were the dominant factors affecting the abundances of N-cycling genes. Long-term application of OM and NM can promote N cycling by enhancing gene abundance due to increased soil organic matter and microbial biomass compared to NF and CK.

Acid Mine Drainage Treatment by Potential Carbon Mineralization: A Step Toward a Circular Economy

Acid Mine drainage is produced mainly from the two sources such as mineral and mining industries and there are a factors to enhance the AMD formation: i) atmospheric moisture, ii) pH, iii)temperature, and iv) surface area of sulfide minerals exposed to the oxygen. Acid Mine Drainage (AMD) is formed with the outflow of extremely acidic water from the mine dumps or abandoned mine sites, which contains the dissolved heavy metals such as Copper (Cu), Lead (Pb), Mercury (Hg), Nickel (Ni), Arsenic (As), Cobalt (Co), Cadmium (Cd), and other some common metals are Manganese (Mn), Iron (Fe), and Zinc (Zn). AMD is a major pollutant that causes a severe threat to the aquatic and ecosystem. There are a few major issues associated with this AMD including contamination of drinking water, lowering the reproduction growth rate of plants and aquatic animals, etc. In this paper, we discussed a new technical solution carbon mineralization technology for the treatment of acid mine drainage, and also promoting the possible circular economy was proposed. A carbon mineralization technology was studied for the stabilization of heavy metals in soil and ashes as well as hardness removal of water. The proposed carbon mineralization is an alternative technical solution for the treatment of AMD which leads the AMD wastewater to be a resource to achieve a circular economy.

How soil carbon fractions relate to soil properties and crop yields in dryland cropping systems?

AbstractSoil labile C fractions have been proposed as promising soil health indicators, but they have not been related to extensive soil properties and crop yields. We evaluated the relationships among soil organic carbon (SOC), labile C fractions, 62 soil physical, chemical, biological, and biochemical properties, and mean crop yields in two long‐term (14‐ and 36‐yr‐old) sites (Froid and Sidney, eastern Montana) under dryland farming. Soil C fractions were SOC, soil inorganic carbon (SIC), water‐extractable carbon (WEC), KMnO4–extractable carbon (POXC), potential carbon mineralization (PCM), and microbially active carbon (MAC). Treatments were conventional till and no‐till spring wheat (Triticum aestivum L.)/barley (Hordeum vulgaris L.), pea (Pisum sativum L.), and fallow rotations without N fertilization in Froid and with and without N fertilization in Sidney. Carbon fractions were greater in no‐till continuous cropping than till crop–fallow, with no effect of N fertilization at both sites. The principal component analysis showed that PCM was strongly associated with most soil physical, chemical, biological, and biochemical properties, followed by SOC, POXC, WEC, MAC, and SIC at both sites. More C fractions were related to soil properties in longer than shorter duration of the experiment. All C fractions, except SIC, were also related to mean crop yields across years. Although SOC was related to soil properties and crop yields, PCM may be used as a promising soil health indicator because of its greater sensitivity to management practices and better relationship to soil properties and crop yields than other labile C fractions.

Linking soil microbial community structure to potential carbon mineralization: A continental scale assessment of reduced tillage

Potential carbon mineralization (Cmin) is a commonly used indicator of soil health, with greater Cmin values interpreted as healthier soil. While Cmin values are typically greater in agricultural soils managed with minimal physical disturbance, the mechanisms driving the increases remain poorly understood. This study assessed bacterial and archaeal community structure and potential microbial drivers of Cmin in soils maintained under various degrees of physical disturbance. Potential carbon mineralization, 16S rRNA sequences, and soil characterization data were collected as part of the North American Project to Evaluate Soil Health Measurements (NAPESHM). Results showed that type of cropping system, intensity of physical disturbance, and soil pH influenced microbial sensitivity to physical disturbance. Furthermore, 28% of amplicon sequence variants (ASVs), which were important in modeling Cmin, were enriched under soils managed with minimal physical disturbance. Sequences identified as enriched under minimal disturbance and important for modeling Cmin, were linked to organisms which could produce extracellular polymeric substances and contained metabolic strategies suited for tolerating environmental stressors. Understanding how physical disturbance shapes microbial communities across climates and inherent soil properties and drives changes in Cmin provides the context necessary to evaluate management impacts on standardized measures of soil microbial activity.

Carbon mineralization potential of non-edible oil-seed cakes at different composting stages in soil

Non-edible oil-seed cakes of neem, madhuca and simarouba were subjected to natural decomposition by simple pit method in CR design during 2020–21 at UAS, GKVK, Bangalore. The physicochemical parameters temperature, pH, EC, mineral nutrients, lignin contents and phytotoxicity of oil-seed cakes during decomposition were determined at 30 days intervals for 90 days. Simultaneously, samples were also studied for the C-mineralization pattern by measuring CO2-C evolution during 60 days of the aerobic incubation experiment. The first-order kinetic model was used to describe the C-mineralization and calculate potentially mineralizable C. The decomposition of oil-seed cakes led to an increase in mineral nutrients and a decrease in lignin content and toxicity. After 60 days of the addition of soil with oil-seed cakes at different stages of compost, the cumulative C-mineralization occurred in the order neem&lt;madhuca&lt;simarouba. The kinetic model suggested the presence of potentially mineralizable C (C0) in the undecomposed simarouba oil-seed cake than in the neem and madhuca. This C0 decreased at 90 days of composting in all oil-seed cakes. The NMC was high in undecomposed oil-seed cakes in the order S-0&gt;M-0&gt;N-0. The CMC value of mature compost (90 days) was lower in neem and simarouba (6%) than in madhuca oil-seed cakes (22%). The low C-mineralization potential of raw and composted neem oil-seed cake suggested its superiority in the improvement of SOC. However, complete composting of oil-seed cakes of madhuca and simarouba was necessary for C-sequestration.

Evaluating forest soil quality after deforestation and loss of ecosystem services using network analysis and factor analysis techniques

This study aimed to establish a soil quality index (SQI) using factor analysis (FA) and network analysis (NA) techniques for the assessment of soil quality after deforestation in Northern Iran. In this work, 16 soil properties from forest sites and adjacent cropland sites at two locations in the Hyrcanian forests of Northern Iran were used and analyzed. The minimum data set (MDS) indicators selected through the FA method were potential carbon mineralization (PCM), urease activity (URE), plant-available water and cation exchange capacity, which contributed to the SQI value by 39, 28, 19 and 13%, respectively. Soil quality indicators identified through the NA approach were URE, organic C (OC), PCM and microbial biomass C (MBC), contributing towards the SQI value by 34, 26, 23 and 17%, respectively. The PCM and URE, selected by both techniques, were the most significant indicators of soil quality to detect the deforestation impacts in Northern Iran. The computed SQIs were significantly correlated with OC stocks, validating the SQI models developed by both FA and NA methods. The SQI values computed through NA were more sensitive to deforestation than those computed through FA, suggesting the NA-screened SQI would represent changes in soil functions more adequately than the FA-screened SQI. Croplands were characterized by a lower value of SQI (62–79%), especially in the surface layer, indicating a loss of soil capacity to function well after deforestation for the expansion of farmlands. The current study shows that the SQI model developed by the NA approach would also be a useful, alternative technique for soil quality assessment after conversion of native forest ecosystems to agricultural lands. To conclude, our results confirmed a weighted correlation-based NA of the soil attributes can be used as a simple and robust tool for assessing soil quality following deforestation and loss of ecosystem services.

Factors controlling soil organic carbon stocks in hardwood floodplain forests of the lower middle Elbe River

We assessed key relationships of soil organic carbon (SOC) stocks to hydromorphic features, soil texture, C/N ratio, pH, and forest age in hardwood floodplain forests. Floodplain ecosystems play a significant role in the global carbon cycle, particularly due to their SOC storage potential. Interactions between heterogeneous micro-relief and anthropogenically affected vegetation and the hydrologic situation of floodplains make predicting SOC stocks difficult without field validation. Especially within hardwood floodplain forests, the controlling factors for SOC storage remain understudied, whereas these floodplain types can be the largest reservoir for carbon and have a substantial SOC sequestration potential. To determine the controlling factors for SOC storage, we selected 38 hardwood floodplain forest and 11 floodplain grasslands of the lower middle Elbe River and categorized them according to vegetation type (grassland, young forest, or old forest) and hydrologic situation (low-lying or high elevated and active or former floodplain). Profile SOC stocks were determined to a depth of 1 m, and topsoil SOC stocks were related to vegetation and soil characteristics, particularly pedological traits (e.g., hydromorphic features).Forest SOC stocks ranged between 99 and 149 t ha−1. SOC stocks decreased with depth throughout all categories and were unaffected by vegetation type within the same hydrologic situation. Vegetation parameters such as age, basal area, or leaf litter carbon stock had no direct effect on SOC stocks. An active connection to the river had the strongest effect on SOC stocks, with former floodplain sites storing 33% less SOC than the active sites. Within the active floodplains, low sites stored 50% more SOC than high sites. This effect was mainly controlled by relief-affected features such as flooding duration and fine texture, which also were the strongest univariate predictors for SOC stocks (R2 = 0.39 and 0.63). A multiple linear regression showed that fine texture, pH, C/N ratio and forest age can be used to explain 86% of variance in SOC stocks.We conclude that proxies for relief and sedimentation (i.e., hydromorphic features, flooding duration, soil texture, C/N ratio, and pH) are the strongest factors controlling SOC stocks in hardwood floodplain forests. Both can be related to allochthonous carbon inputs, increasing SOC stabilization through the accumulation of fine soil particles, and decreasing aerobic carbon mineralization potential through oxygen scarcity, while vegetation plays only a subordinate role.

Fertilization enhances mineralization of soil carbon and nitrogen pools by regulating the bacterial community and biomass

The stability of soil organic matter is a key predictor of changes in management practices due to the progressive decomposition of organic compounds. However, the dynamics of soil compounds and to what extent the composition of microbes controls the process are still unclear. Black soils from Northeast China without fertilizer (CK), soil treated with chemical fertilizer (NPK), NPK plus maize straw (NPKS), and NPK plus cattle manure (NPKM) were collected and separated into the labile fraction (macroaggregates > 150 μm) and the recalcitrant fraction (microaggregates 150 μm) for a 14-day incubation. The net carbon (C) and net nitrogen (N) mineralization potentials of the labile fraction were 15.87–26.11 and 0.74–1.48 mg kg−1 soil day−1, respectively, which were between 1.4 and 2.3 times higher than those of the recalcitrant fraction. Compared with CK, NPKS and NPKM significantly increased C and N mineralization in the labile fraction but not in the recalcitrant fraction. Boosting regression tree analysis suggested that total nitrogen (TN), microbial biomass nitrogen (MBN), and bacterial abundance accounted for 48.9%, 31.7%, and 14.0% of the total net C mineralization, respectively. Additionally, soil organic carbon (SOC), microbial biomass carbon (MBC), and bacterial abundance accounted for 39.4%, 37.3%, and 22.1% of the total net N mineralization, respectively. Path analysis showed that TN, MBN, and Brevundimonas positively influenced soil net C mineralization. SOC and MBC positively affected soil net N mineralization, whereas unclassified Comamonadaceae had a negative impact. The mineralization of soil C and N was affected by the inputs of external inorganic nutrients and organic materials and was attributed to the bacterial community, in which Brevundimonas positively responded and contributed to mineralization, while unclassified Comamonadaceae responded negatively.

Synergistic effects of antimony and arsenic contaminations on bacterial, archaeal and fungal communities in the rhizosphere of Miscanthus sinensis: Insights for nitrification and carbon mineralization

The impacts of metal(loids) on soil microbial communities are research focuses to understand nutrient cycling in heavy metal-contaminated environments. However, how antimony (Sb) and arsenic (As) contaminations synergistically affect microbially-driven ecological processes in the rhizosphere of plants is poorly understood. Here we examined the synergistic effects of Sb and As contaminations on bacterial, archaeal and fungal communities in the rhizosphere of a pioneer plant (Miscanthus sinensis) by focusing on soil carbon and nitrogen cycle. High contamination (HC) soils showed significantly lower levels of soil enzymatic activities, carbon mineralization and nitrification potential than low contamination (LC) environments. Multivariate analysis indicated that Sb and As fractions, pH and available phosphorus (AP) were the main factors affecting the structure and assembly of microbial communities, while Sb and As contaminations reduced the microbial alpha-diversity and interspecific interactions. Random forest analysis showed that microbial keystone taxa provided better predictions for soil carbon mineralization and nitrification under Sb and As contaminations. Partial least squares path modeling indicated that Sb and As contaminations could reduce the carbon mineralization and nitrification by influencing the microbial biomass, alpha-diversity and soil enzyme activities. This study enhances our understanding of microbial carbon and nitrogen cycling affected by Sb and As contaminations.

Carbon storage and mineralization potential of soils under major plantation crops in the Western Ghats region of Kerala

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Kinetics of Soil Carbon Mineralization Under Continuous Site-Specific Nutrient Management in Ultisols Under Cassava

ABSTRACT The present study focused on the effect of 10 years of continuous fertilizer trials on soil organic carbon (SOC) mineralization in cassava grown ultisols. The study determines the carbon (C) mineralization potential, dynamics, and kinetics of C mineralization by fitting five decay models, significance of various long-term fertilizer applications on C mineralization and the relationship between soil physico-chemical properties with carbon mineralization parameters derived from the best model. To determine the potential of the soil to mineralize organic C a short-term aerobic incubation procedure – alkali trap method – was used. The best model fitting first-order E (R2 = 0.994) was used to describe the dynamics and kinetics of C mineralization. Relationships between soil physico-chemical properties and C mineralization parameters of first-order E model were studied by using correlation analysis. The site-specific nutrient management (SSNM) treatment showed the highest carbon dioxide-carbon (CO2-C) evolution value (2049.61 mg of CO2-C kg−1 soil) while NPK omission treatment showed the lowest (1703.37 mg of CO2-C kg−1 soil). The initial potential rate of carbon mineralization (C0k) was highest for SSNM treatment (159.78 mg kg−1) and lowest for K omission treatment (123.25 mg kg−1) indicating that the organic matter quality has increased in continuous SSNM treatment for 10 years compared to all other treatments. Significant positive correlations were shown between cumulative C evolved (Cm) and SOC. Significant negative correlations were observed between size of the mineralization flush (C1) and silt as well as between potentially mineralizable carbon (C0K) and clay.

Variations in soil organic carbon decompositions of different land use patterns on the tableland of Loess Plateau.

Land use patterns are one of the critical factors affecting soil carbon sequestration or decomposition and greenhouse gas emissions. The accurate evaluation of its change is particularly crucial for the carbon cycle of the terrestrial ecosystem and global climate change. This paper examined the dynamic soil respiration by means of the indoor airtight culture method and static box-gas chromatography under the land uses of the farmland, natural grassland, shrub forestland, arbor and shrub mixed forestland, and arbor forestland on the tableland of Loess Plateau. The results showed that soil organic carbon mineralization and soil respiration rate were influenced by the land use type. (1) The content and rate of soil mineralizable carbon in grassland were significantly higher than that in forestland and farmland, and that in forestland significantly higher than that in the farmland (P < 0.05). The trend of organic carbon mineralization was rapid in the initial stage of culture (by the rate of 30.02~238.56mgkg-1h-1 in the first 0.5h) and slowed down in the later stage (by the rate of 1.07~1.95mgkg-1h-1 in 1575h). In the soil of grassland, the accumulation of mineralizable organic carbon in the 0-5-cm layer was 1.20~1.64 times that in the soil of forestland and 1.82 times that of farmland. Compared with the 0-5-cm soil layer, there were decreases in the 5-20-cm soil layer under all land uses, with a decline of up to 48% in farmland. (2) The soil carbon mineralization potential of different land use types ranged from 0.81 to 2.70mgkg-1, that of grassland was significantly higher than that of farmland (P < 0.05), and the soil organic carbon decomposition rate constant (k) under shrub forestland was significantly higher than that under other land use types (P < 0.05). The highest organic carbon mineralization capacity and the lowest sequestration were in the soil of farmland, while that in grassland had the lowest organic carbon mineralization capacity and the highest sequestration. (3) The cumulative amount of soil respiration was highest under the natural grassland, followed by the shrub forestland, and lowest under the farmland. The soil respiration rate was positively correlated with soil temperature, and its correlation with soil water content was positive in the wet season (May through October) and negative in the dry season (November through April in the following year). (4) The soil respiration rate showed obvious seasonal differences. After the conversion of farmland to forestland, it would be rising in the content of soil organic carbon and labile organic carbon, and be going down in the temperature sensitivity (Q10). In summary, by converting farmland to forestland or grassland, the sequestration of soil organic carbon had greatly been enhanced, and the possibility of soil greenhouse gas emissions had reduced on the tableland of Loess Plateau.

Analyzing vegetation cover-induced organic matter mineralization dynamics in sandy soils from tropical dry coastal ecosystems

To gain knowledge about carbon and nitrogen mineralization potentials and their interaction with sandy soil environment in tropical dry coastal ecosystems, we carried out a short-term laboratory incubation experiment. For this, soil surface (0–10 cm) samples were collected from tropical semi-deciduous forest (TSdF), secondary forest (SecF), coastal dune scrub_crest (DS_C), and coastal dune scrub_slack (DS_S). Soil samples were incubated at 25 °C with constant soil moisture (at field capacity) for 97 days, and over this time 10 and 11 sampling occasions were analyzed to determine carbon (CO2-C) and nitrogen (NH4+, NO3-) dynamics, respectively. We used a simple exponential model to estimate soil carbon and nitrogen mineralization pools. On average, soil organic carbon mineralization rates ranged between 0.017 and 0.053 mg CO2-C g−1 soil d−1 and varied in the following order: DS_S > SecF > TSdF > DS_C. Average net mineralization rates (mg N kg−1 soil d−1) ranged between 16.9 and 18.8 and varied in the following order: SecF > DS_S > TSdF, whereas in DS_C it was −0.44, indicating N immobilization. Co and No represented, on average, 1.08% and 5% of soil organic carbon and total organic nitrogen, respectively. On average, mineralization constants (k) for Co and No were 0.29 d−1 and 0.23 d−1, respectively, showing that SOM is easily mineralized. The proportion of NO3-/Nm was very high in SecF (89%) and TSdF (75%), while DS_C showed nitrate immobilization. The increase in NO3-/Nm ratio in SecF could be associated with legume species that have established in the nature restoration (SecF) on ex-grassland. Across all study sites, linear regression analyses suggested that soil physical and chemical properties may regulate SOM mineralization (p < 0.05).

Past aridity's effect on carbon mineralization potentials in grassland soils

Abstract. Mineralization potential is a key property for assessing carbon substrate's degradability and mineralization in biogeochemical models and studies. While mineralization potential is widely examined under controlled conditions, whether and how it is influenced by the past aridity of sample's origins remain poorly constrained, which is important for an accurate assessment and prediction of future CO2 emissions. Here we collect topsoils and subsoils from different aridity regimes along a 2100 km grassland transect of northern China and conduct a 91 d decomposition experiment with and without the addition of 13C-labeled leaf litter under controlled temperature and moisture. CO2 release from both soil organic carbon (SOC) and fresh litter is measured, along with microbial biomass, extracellular enzyme activities, and soil and mineral properties. We find that neither microbial carbon use efficiency nor biomass-normalized metabolic quotient (qCO2) is related to the aridity of sampling sites. However, both fresh litter and SOC display the highest mineralization potentials in soils originating from the driest site. Using pathway analysis, we demonstrate that past aridity's effect is mediated by differential mechanisms for substrates of varied complexity. While microbial biomass plays a more important role in the decomposition of fresh litter, enzyme-catalyzed extracellular reactions predominantly govern the mineralization of SOC. Our findings provide novel evidence on the mechanisms underlying past aridity's effect on the mineralization potentials of organic matter with different qualities, which has significant implications for assessing and modeling decomposition in different aridity regimes.