Soil Carbon Mineralization Research Articles

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.

Effect of Wheat Straw Addition on Organic Carbon Mineralisation and Bacterial Community in Orchard Soil

Crop straw returning can stimulate organic carbon mineralisation and C sequestration simultaneously, which affects soil fertility. However, the effects of crop straw on organic carbon mineralisation and soil bacterial community in orchards are not fully understood. A 90-day incubation experiment was performed to investigate the effects of wheat straw (0, 1, 4, 6, 8, and 10 t·ha−1) on organic carbon mineralisation and bacterial community in orchard soil. Wheat straw addition enhanced the CO2 efflux rate and cumulative organic carbon mineralisation (Cmin), especially high level. The trend of CO2 efflux rate was increased sharply, especially during the early incubation stage (the first 13 days), and then decreased in the later phase. Furthermore, soil bacterial community structure displayed distinct changes in response to straw addition. Available nitrogen, potassium, organic carbon, β-glucosidase, and pH were the key factors driving soil bacterial community changes. The bacterial taxa in networks were significantly related to Cmin. The Proteobacteria, Actinobacteria, and Chloroflexi were positively related to Cmin; while Planctomycetes, Patescibacteria, and Gemmatimonadetes showed a negative relationship with Cmin by correlation and redundancy analyses. Co-occurrence network analysis showed a discrete bacterial network in 10 t·ha−1 of straw, while cohesive networks in others. Straw addition promoted organic carbon mineralisation by improving the soil biochemical properties, including enzymes activities, and nutrient contents, and regulating bacterial community composition. On the whole, 4 t·ha−1 of straw could be considered an economical level for improving soil organic carbon and bacterial community stability in orchards.

Influence of Poultry Litter Biochar on Some Properties and Carbon Mineralization in Acidic Soil

During the last years, biochar (BC) from various organic wastes and its application to soil to improve soil properties have been a very common treatment in agricultural soils. While many studies have been conducted on the effects of biochar on the improvement of alkaline soils, studies on acid soils are limited. An incubation experiment was conducted to investigate the effects of poultry litter biochar (PLBC) on acidic soil properties and C mineralization. Biochar derived from poultry litter (PLBC) through slow pyrolysis was mixed with soil in three different doses (0, 2, and 5%) and subjected to a 120-day incubation period. pH increased from 4.38 to 5.31 at the end of the incubation. Electrical conductivity (EC) values also increased. Carbon dioxide (CO2) emission reached its maximum on the 30th day of the incubation in control and with PLBC applied to the soil. PLBC increased the organic matter (OM) content of the soil. Values were 3.51%, 4.70%, 6.27% for control, PLBC 2% and 5% treatments, respectively. PLBC does have an increasing negative priming effect on the carbon (C) mineralization of the soil. Particulate organic matter (POM) increased the storage of organic carbon (OC) in the POM fraction for both PLBC applications. It is revealed that PLBC showed soil conditioning effect as well as C storage in the soil. This study was on the short-term incubation under controlled conditions, varying results would be obtained in field conditions.

Exploring the mystery of soil carbon mineralization: Insights from incubation experiments and kinetic modeling

Soil carbon mineralization is vital for carbon sequestration but affected by factors like soil type and residue quality. Understanding the process and factors is still incomplete, including the interplay between soil properties and organic residues and the need for accurate kinetic models. Research faces significant challenges in describing carbon mineralization dynamics. The present study aimed to investigate carbon mineralization in three soils located in Tamil Nadu, India (S1, S2 and S3) that possess distinct textures. The study also focused on the effects of five different plant residues (Rice, maize, sugarcane, cotton and turmeric) on carbon mineralization in these soils. Incubation experiments were conducted for 150 days, and CO2 evolution was measured at different time intervals of 7, 10, 15, 30, 60, 90, 120 and 150 days. The performance of three kinetic models (Zero order model, exponential kinetic model and first order model) was also evaluated in predicting carbon mineralization using experimental data. The results showed that the rate and extent of carbon mineralization varied significantly among the different soils and residues. The highest carbon mineralization was observed in rice (989.02 µg C/g/day) and maize (966.53 µg C/g/day) residue, while the lowest was in sugarcane (752.09 µg C/g/day) residue. Among the kinetic models, the first-order kinetic model provided the best fit for all treatments (R2=0.98). The findings suggest that soil texture and residue quality play crucial roles in carbon mineralization. The first order kinetic model can be useful for predicting carbon mineralization in different soil-residue systems. These results have implications for managing soil carbon sequestration and mitigating climate change.

Microsite Determines the Soil Nitrogen and Carbon Mineralization in Response to Nitrogen Addition in a Temperate Desert

Nitrogen deposition can change the soil in N and C cycling processes. However, a general understanding of how N deposition changes C and N mineralization has not yet been reached. Soil organic C and N mineralization beneath the dominant shrubs of Haloxylon ammodendron and between the shrubs in response to two levels of N addition (2.5 gN m−2 and 5 gN m−2 per year) were investigated in the 1st, 4th, and 9th year of N addition in a temperate desert of northern China. N addition promoted soil N mineralization (RmN), and the nitrification rate (RNN) increased C mineralization in the interplant and decreased it beneath shrubs. N addition increased soil microbial biomass C (Cmic), N (Nmic), and PLFAs in the interplant, and decreased it beneath shrubs. RmN and RNN were related to Nmic, and RCM was related to Cmic and the total PLFAs. N addition increased the fungal biomass alongside the ratio of fungal to bacterial PLFAs in the interplants while decreasing them beneath shrubs. Our results support how N addition can increase soil N mineralization and nitrification, but the effects on soil C mineralization are dependent on the amount of nitrogen addition, the soil’s available carbon content, and water. Finally, the divergent responses of microbial communities to N addition between microsites suggest that the “fertile islands” effects on nutrients and microbial biomass are important when estimating feedbacks of C and N cycling to projected N deposition in the desert ecosystem.

The Mineral Characteristic of Tropical Residual Soil using X-Ray Diffraction (XRD) and Scan Electron Microscopy (SEM)

Volcanic residual soil has unique characteristics due to weather and morphological influences. High temperatures and large amounts of rainfall made the rock weathering intense. Landslide events in volcanic residual soil of West Java are quite serious, more than 100 incidents in total a year. Landslides that occur due to unsaturated conditions on the top of the slope become saturated, so it is very important to conduct research on these tropical residual soil weathering zones to define its mineral characterization using Scan Electron Microscopy (SEM) and X-Ray Diffraction (XRD). From the research it was found that the dominant mineral types and contents were Halloysite and Kaolinite minerals. A typical mineral profile is found that is Goethite and Hematite minerals at the soil surface, Carbonate and Chlorite minerals in deeper soils and large amounts of Feldspar minerals in more deep layers. Because there are unique minerals at each depth of soil weathering, zone classification can be done easily starting from the Initial Leaching Zone at the deepest part where there is Feldspar, the Mineral Washing Zone there is Carbonate and Chlorite and the Oxidation Zone on the surface (there are Oxide and Hydroxide minerals). So that it can form a Residual Tropical Volcanic Weathering Profile.

Are carbon-storing soils more sensitive to climate change? A laboratory evaluation for agricultural temperate soils

A range of agroecological practices allow to increase soil organic carbon (SOC) stocks, which makes a positive impact on climate change mitigation and soil health, but the permanence of this additional SOC storage can be questioned, in particular in a climate change context. Increased temperatures, accentuated evaporation of terrestrial water and increased atmosphere moisture content are anticipated, resulting in more frequent droughts and heavy precipitation events. Understanding the SOC dynamics and assessing the sensitivity of carbon mineralization to these climatic events is necessary to anticipate future carbon losses in terrestrial ecosystems. To this respect, it seems relevant to investigate carbon-storing soils as increased carbon mineralization induced by climate change may limit the carbon storing potential in agricultural soils. Thus, we evaluated the sensitivity of SOC mineralization to increased temperature, decreased soil moisture and drying-rewetting cycles using soils from long-term field experiments. We performed an incubation experiment on topsoil (0–30 cm) samples from temperate luvisols that had been under 20 years under conservation agriculture (CA), organic agriculture (ORG) and conventional agriculture (CON-LC) at the La Cage experiment, and under organic waste products (OWPs) applications in QualiAgro experiment, including biowaste composts (BIOW), residual municipal solid waste composts (MSW), farmyard manure (FYM) and conventional agriculture without organic inputs (CON-QA). Soil samples were incubated in the lab for 3 months under different temperature conditions (20, 28 and 35 °C) or under different moisture conditions (matric potential: pF1.5; pF 2.5 and pF 4.2) or under several dry (pF 4.2)-wet (pF 1.5) cycles (DWC). The results shown that, whatever the agricultural practices, soil moisture regime and temperature significantly affect the SOC mineralization. Overall, the DWC did not stimulate soil carbon mineralization relative to wet controls (pF1.5 and pF2.5). Whatever the soil moisture regime and temperature, specific carbon mineralization was similar between agricultural practices at La Cage, while at QualiAgro, specific carbon mineralization was lower in soils receiving organic waste products (OWPs) compared to the baseline soil. These results suggest a strong carbon stabilization by OWPs in soils as assessed by laboratory incubation experiments. Within each long-term experiment, we observed no significant difference between the carbon-storing soils (CA, ORG, MSW, FYM and BIOW) and their respective baseline soils (CON-LC and CON-QA) in the delta SOC mineralized whatever the soil moisture regime. The Q10 also indicated no significant difference between carbon-storing soils and their respective baseline soils. These results indicate that the SOC mineralization in carbon-storing soils had a similar sensitivity to the soil moisture regime and temperature as the baseline ones. Hence, the implementation of these agroecological practices appears beneficial for climate change mitigation, even in the context of extreme climatic events.

The Contribution of Fe(III) Reduction to Soil Carbon Mineralization in Montane Meadows Depends on Soil Chemistry, Not Parent Material or Microbial Community

AbstractThe long‐term stability of soil carbon (C) is strongly influenced by organo‐mineral interactions. Iron (Fe)‐oxides can both inhibit microbial decomposition by providing physicochemical protection for organic molecules and enhance rates of C mineralization by serving as a terminal electron acceptor, depending on redox conditions. Restoration of floodplain hydrology in montane meadows has been proposed as a method of sequestering C for climate change mitigation. However, dissimilatory microbial reduction of Fe(III) could lead to C losses under increased reducing conditions. In this study, we explored variations in Fe‐C interactions over a range of redox conditions and in soils derived from two distinct parent materials to elucidate biochemical and microbial controls on soil C cycling in Sierra Nevada montane meadows. Soils derived from basalt showed greater rates of Fe(III)‐reduction at increasing soil moisture levels than granitic soils. Increases in Fe(III) reduction, however, were only associated with elevated rates of C mineralization in one basalt soil. Known Fe(III)‐reducing taxa were present in all samples but neither the relative abundance nor richness of Fe(III)‐reducers corresponded with measured rates of Fe(III) reduction. Under reducing conditions, Fe(III)‐reduction was only coupled to C mineralization in the soil with the greatest amount of Fe‐oxide bound C. However, Fe‐oxide ‐bound C was below theoretical limits for C sorption onto Fe‐oxides and not detectable in all soils. Overall, our results suggest that “what's there” in terms of soil chemistry may be a more important driver of C mineralization coupled to Fe(III) reduction than “who's there” in the microbial community.

Effect of Different Bacterial Fertilizers on Soil Carbon Mineralization

In this study, aimed to investigate the effect of bacterial fertilizer: A (Bacillus spp., Trichoderma spp. ), B (Azorhizobium, Azotobacter and Azospirillum) and C (Azotobacter spp., Bacillus spp. and Pseudomonas putida) on soil carbon mineralization. On the application of A, B and C bacterial fertilizers on the sterilized control soil, whose initial carbon mineralization rates is 1.1%, mineralization rates of 5.12%, 3.54%, and 10.78% were respectively recorded. According to these results, it was observed that the application of bacterial fertilizer increased the carbon mineralization rate of the sterilized control soil by 365.45%, 221.82% and 880%, respectively. A carbon mineralization rate of 7.03%, 6.15% and 12.95% was recorded in the non-sterilized soil sample whose initial carbon mineralization rate is 5.1%, thereby increasing the mineralization rate by 25.31%, 9.63% and 130.84%. The application of the bacterial fertilizer to the soil was found to increase the soil carbon mineralization rate. It is recommended to incorporate bacterial fertilizers with CO2- sequestering materials, such as biochar, to mitigate the fluctuations in the natural balance due to carbon release.

Variations in the soil micro-food web structure and its relationship with soil C and N mineralization during secondary succession of subalpine forests

The soil micro-food web is an important network of belowground trophic relationships and it participates directly and indirectly in soil ecological processes. In recent decades, the roles of the soil micro-food web in regulating ecosystem functions in grasslands and agroecosystems have received much attention. However, the variations in the soil micro-food web structure and its relationship with ecosystem functions during forest secondary succession remain unclear. In this study, we investigated how forest secondary succession affected the soil micro-food web (including soil microbes and nematodes) and soil carbon and nitrogen mineralization across a successional sequence of “grasslands – shrublands – broadleaf forests – coniferous forests” in a subalpine region of southwestern China. With forest successional development, the total soil microbial biomass and the biomass of each microbial group generally increased. The significant influences of forest succession on soil nematodes were mainly reflected in several trophic groups with high colonizer-persister values (particularly bacterivore3, herbivore5 and omnivore-predator5) that are sensitive to environmental disturbance. The increases in the connectance and nematode genus richness, diversity, and maturity index indicated an increasingly stable and complex soil micro-food web with forest succession, which was closely related to soil nutrients, particularly the soil carbon contents. Additionally, we found that the soil carbon and nitrogen mineralization rates also exhibited generally increasing trends during forest succession, which had significant positive correlations with the soil micro-food web composition and structure. The path analysis results indicated that the variances in ecosystem functions induced by forest succession were significantly determined by soil nutrients and soil microbial and nematode communities. Overall, these results suggested that forest succession enriched and stabilized the soil micro-food web and promoted ecosystem functions via the increase in soil nutrients, and the soil micro-food web played an important role in regulating ecosystem functions during forest succession.

Effects of warming on quantity and structure of litter-derived dissolved organic matter in subtropical natural Castanopsis kawakamii forests.

Litter-derived dissolved organic matter (DOM) is an important source of soil DOM, and the response of which to climate warming may change forest soil carbon and nitrogen dynamics, such as soil carbon and nitrogen mineralization. In this study, we conducted a field manipulative warming experiment in natural Castanopsis kawakamii forests. Combined with litter leaching solution collected in the field and ultraviolet-visible and three-dimensional fluorescence spectroscopy analyses, we explored the effects of warming on the content and structure of litter-derived DOM in subtropical evergreen broad-leaved forests. The results showed that litter-derived dissolved organic carbon and nitrogen content exhibited monthly dynamics, with the peak (in April) and the mean monthly content being 1.02 and 0.15 g·m-2, respectively. Litter-derived DOM had higher fluorescence index and lower biological index, indicating the microbial-origin of DOM from litter. The litter DOM mainly included humic-like fractions and tryptophan-like substances. Warming did not affect the content, aromaticity, hydrophobicity, molecular weight, fluorescence index, biological index and humification index of DOM, suggesting neutral effect of warming on the quantity and structure of litter DOM. Warming also did not affect the relative contribution of main components in DOM, indicating that the temperature variation exerted no effects on microbial degradation. In summary, warming did not change the quantity and quality of litter-derived DOM in subtropical evergreen broadleaved forests, indicating warming had little effect on litter-derived DOM input to soil.

Wollastonite addition stimulates soil organic carbon mineralization: Evidences from 12 land-use types in subtropical China

Enhanced rock weathering through adding silicate rock powder to soil has been increasingly considered as an effective means of removing CO2 from the atmosphere. However, the potential impact of silicate rock powder addition on the stability of soil organic carbon remains largely unknown, which adds an uncertainty to its effectiveness in mitigating atmospheric CO2. In this study, the response of soil CO2 efflux to wollastonite addition was evaluated for 12 land-use types in a subtropical region of China through an incubation experiment. Results showed that wollastonite addition significantly (P < 0.05) increased soil CO2 efflux over the control by an average of 330.97 ± 29.25% during the incubation period. Approximately 90% of the variance in soil CO2 efflux was explained by soil properties in this study. Increased soil pH, dissolved organic carbon and available silicon induced by wollastonite addition were the main reasons responsible for the increase in soil CO2 emission. Soils having lower pH values responded to wollastonite addition with a higher increase in CO2 emissions. Based on numerous land-use types, our study showed that wollastonite application will cause substantial increase in the mineralization of soil organic carbon in acidic soil, which may weaken the effectiveness of enhanced rock weathering strategies as a tool for CO2 sequestration.

New insights into carbon mineralization in tropical paddy soil under land use conversion: Coupled roles of soil microbial community, metabolism, and dissolved organic matter chemodiversity

Although the impact of land conversion on carbon mineralization in paddy soils has received increasing attention, the coupled roles of soil microdiversity and chemodiversity in these processes are largely unknown. To address this issue, the land use conversion from paddy fields (PF) to vegetable fields (VF), rice-vegetable rotation (RV), and abandoned land (AL), were investigated in this study. The relationships between soil mineralization characteristics and microbial community, metabolism physiology and dissolved organic matter (DOM) chemodiversity were analyzed. After the conversion, soil mineralization enhanced in AL and RV, which were 217.49% and 183.02% of that in PF. In contrast, no significant change was observed in VF, although the anaerobic environment was transformed into an aerobic one and the fungal richness/ diversity increased in the soil. This was because soil mineralization was directly regulated by DOM quantity and microbial metabolism of labile carbon, and indirectly by DOM chemodiversity and microbial community. Specifically, the largest mineralization in AL was attributed to the strongest microbial metabolism of labile carbon, as AL had the largest DOC contents, hydrophilic substances (e.g., carboxyl, carbohydrate, and amino), and abundant eutrophic taxa (e.g., Actinobacteria and Proteobacteria). In contrast, no significant change in VF was mainly related to more condensed aromatics and oligotrophic microbes, and fewer DOC in soil, resulting in the dominance of microbial metabolism of soil recalcitrant carbon. The recalcitrant carbon metabolism also prevailed in RV. However, RV showed moderate soil mineralization due to having the proper DOM with high bioavailability. Collectively, the results provide molecular insights into the impact of land conversion on soil mineralization from a micro-chemodiversity perspective, which highlights the importance of nutrient supply and microbial metabolism strategy.

Moisture-dependent response of soil carbon mineralization to temperature increases in a karst wetland on the Yunnan-Guizhou Plateau.

Wetlands are facing gradual drying, leading to large carbon loss due to the transformation from anaerobic to aerobic conditions, but the temperature and drought effects from the temperature and moisture fluctuation on soil organic carbon (SOC) mineralization remain uncertain. An incubation study with three moisture levels (100%, 60%, and 40% WHC, marked as W100, W60, and W40, respectively) and four temperature levels (5, 10, 15, 20°C, marked as T5, T10, T15, and T20, respectively) was conducted to determine the effect of temperature and moisture interactions on SOC mineralization in the karst wetland of the Yunnan-Guizhou Plateau. Compared with T5, the cumulative mineralization CO2 in T20 increased by 83.18% (W40), 154.63% (W60), and 148.16% (W100), respectively. The mineralized CO2 at W60 and W40 significantly decreased compared to that at W100 at the four temperature levels. Temperature, moisture and their interactions had significant positive effects on SOC mineralization rates and cumulative mineralized CO2. The temperature sensitivity of SOC mineralization rates (Q10) under W40 and W60 increased by 22.03% and 24.52%, respectively, compared to that under W100. The cumulative mineralized CO2 was positively related to soil urease activity and negatively related to soil pH, N-NH4+, SOM, and catalase activity. Temperature and moisture fluctuation and soil properties explained 85.40% of the variation in SOC mineralization, among which temperature and moisture fluctuation, soil properties, and their interactions explained 19.71%, 4.81%, and 60.88%, respectively. Our results indicated that SOC mineralization is influenced by the joint effect of temperature and drought, as well as their induced changes in soil properties, in which higher temperatures can increase soil CO2 emissions by enhancing the SOC mineralization rate, but the positive effect may be weakened from the drying wetland.

Effects of magnesium-modified biochar on soil organic carbon mineralization in citrus orchard.

In order to investigate the carbon sequestration potential of biochar on soil, citrus orchard soils with a forest age of 5 years was taken as the research object, citrus peel biochar (OBC) and magnesium-modified citrus peel biochar (OBC-mg) were selected as additive materials, and organic carbon mineralization experiments were carried out in citrus orchard soil. OBC and OBC-Mg were applied to citrus orchard soils at four application rates (0, 1, 2, and 4%), and incubated at a constant temperature for 100 days. Compared with CK, the cumulative mineralization of soil organic carbon decreased by 5.11% with 1% OBC and 2.14% with 1% OBC-Mg. The application of OBC and OBC-Mg significantly increased the content of soil organic carbon fraction, while the content of soil organic carbon fraction was higher in OBC-Mg treated soil than in OBC treated soil. Meanwhile, the cumulative mineralization of soil organic carbon was significantly and positively correlated with the activities of soil catalase, urease and sucrase. The enzyme activities increased with the cumulative mineralization of organic carbon, and the enzyme activities of the OBC-Mg treated soil were significantly higher than those of the OBC treated soil. The results indicated that the OBC-Mg treatment inhibited the organic carbon mineralization in citrus orchard soils and was more favorable to the increase of soil organic carbon fraction. The Mg-modified approach improved the carbon sequestration potential of biochar for citrus orchard soils and provided favorable support for the theory of soil carbon sink in orchards.

Conventional and Zero Tillage with Residue Management in Rice–Wheat System in the Indo-Gangetic Plains: Impact on Thermal Sensitivity of Soil Organic Carbon Respiration and Enzyme Activity

The impact of global warming on soil carbon (C) mineralization from bulk and aggregated soil in conservation agriculture (CA) is noteworthy to predict the future of C cycle. Therefore, sensitivity of soil C mineralization to temperature was studied from 18 years of a CA experiment under rice-wheat cropping system in the Indo-Gangetic Plains (IGP). The experiment comprised of three tillage systems: zero tillage (ZT), conventional tillage (CT), and strip tillage (ST), each with three levels of residue management: residue removal (NR), residue burning (RB), and residue retention (R). Cumulative carbon mineralization (Ct) in the 0-5 cm soil depth was significantly higher in CT with added residues (CT-R) and ZT with added residues (ZT-R) compared with the CT without residues (CT-NR). It resulted in higher CO2 evolution in CT-R and ZT-R. The plots, having crop residue in both CT and ZT system, had higher (p < 0.05) Van't-Hoff factor (Q10) and activation energy (Ea) than the residue burning. Notably, micro-aggregates had significantly higher Ea than bulk soil (~14%) and macro-aggregates (~40%). Aggregate-associated C content was higher in ZT compared with CT (p < 0.05). Conventional tillage with residue burning had a reduced glomalin content and β-D-glucosidase activity than that of ZT-R. The ZT-R improved the aggregate-associated C that could sustain the soil biological diversity in the long-run possibly due to higher physical, chemical, and matrix-mediated protection of SOC. Thus, it is advisable to maintain the crop residues on the soil surface in ZT condition (~CA) to cut back on valuable C from soils under IGP and similar agro-ecologies.

Assessment of soil carbon mineralization and stock in mineralogically different agricultural soils of India

Assessment of soil carbon mineralization and stock in mineralogically different agricultural soils of India

Effects of pyrogenic carbon addition after fire on soil carbon mineralization in the Great Khingan Mountains peatlands (Northeast China)

Wildfires play a critical role in regulating soil carbon (C) budgets in peatland ecosystems, and their frequency and intensity are increasing owing to climate change and human activities. Wildfires not only emit CO2 during the combustion process but also produce pyrogenic carbon (PyC), which accumulates in the soil C pool and influences soil C decomposition. However, the role of PyC after a fire in peatland soil C mineralization has rarely been examined. This study investigated the effects of PyC addition on peatland soil C mineralization and its potential driving mechanisms using an anaerobic/aerobic incubation experiment with peat soils collected from typical peatlands in the Great Khingan Mountains, Northeast China. The effect of PyC was more pronounced under aerobic conditions than under anaerobic conditions. The mean C- mineralization rates of soil were significantly increased by 45.2 ± 15.5 % and 87.6 ± 14.3 % with 10 % PyC250°C addition after the initial stage (D7) of aerobic and anaerobic incubation, but PyC600°C addition caused a to decrease. Compared with PyC600°C, PyC250°C addition significantly increased the available N content and altered the soil microbial activities, which may be the primary reason for the increase in C mineralization rates. Furthermore, adding a high concentration of PyC (10 %) reduced the concentration of phenolics but increased phenol oxidase activity, which promoted C mineralization rates. Thus, PyC250°C addition to peat soils mainly influences the microbial biomass C content through the accumulation of available N and phenolics, which ultimately positively affects C mineralization rates.

Drying-rewetting of permanent pasture and agricultural soils induces a shift towards microbial use of more C-rich organic matter

Rewetting dry soil induces enormous dynamics in microbial growth and biogeochemistry. The temporal dynamics of soil carbon (C) mineralization following drying-rewetting (D/RW) have been widely documented. However, there have been far fewer assessments of gross nitrogen (N) mineralization, and it remains unclear how C and N mineralization dynamics are linked following D/RW events. To address this, soils were sampled from permanent pasture and tilled-and-cropped agricultural fields at two depths (“shallow” soils from 0 to 5 cm depth and “deep” soils from >15 cm depth), with soil C mineralization and gross N mineralization, along with responses in bacterial and fungal growth, measured at high temporal resolution after D/RW. Although soil C mineralization and gross N mineralization were both stimulated by D/RW, the dynamics in C and N mineralization were transiently decoupled. In the cropland soils from both depths, C mineralization peaked immediately and then declined, while N mineralization was sustained at a high level. Similarly, in the deep pasture soil, N mineralization peaked immediately and then declined while C mineralization was maintained at a high level. The shallow pasture was the only soil where C mineralization and N mineralization dynamics were clearly linked after D/RW, both during the first 24 hours, and throughout the 7-day study. Interestingly, in all cases, the ratio of soil C mineralization to N mineralization after D/RW was higher than in moist control soils, suggesting a consistent shift towards microbial use of more C-rich organic matter. The shift was especially pronounced in the pasture soils, where the C-to-N ratio of substrate used after D/RW was more indicative of plant-residues than microbial necromass. The δ13C-signature of respired CO2 was also consistently lower after D/RW compared to that of the moist control – particularly for the pasture soils – providing further evidence that the organic matter used by microorganisms after D/RW was more recently plant-derived than that targeted by microorganisms under optimal moisture conditions. Together, these results highlight that while C and N mineralization are both stimulated by D/RW, changes in mineralization rates do not necessarily occur in parallel, with shifts in the ratio of C-to-N mineralization reflecting shifts in the source of organic matter being used by microorganisms.

Evaluating the Effect on Cultivation of Replacing Soil with Typical Soilless Growing Media: A Microbial Perspective

Bacteria and fungi are good indicators for soil health as well as soilless growing media (SGM) health. However, there is very limited information about the fungal and bacterial communities for SGM. In the present study, coir substrate and peat-based substrate were used as typical SGM under drip irrigation and tidal irrigation to understand the situation of fungal and bacterial communities by high-throughput sequencing technology. In this study, both environmental factors and microbial communities were significantly affected by SGM type and irrigation pattern, in which SGM type played a major role and irrigation pattern played a minor role. The bacterial phyla Actinobacteriota and Proteobacteria and the fungal phyla Ascomycota were more closely related to environmental factors including EC, pH, NO3−, NH4+ and ω as well as urease and phosphatase. The bacterial and fungal communities in the two SGM had some similarities with those in soil. In addition, the functions of the soil, including key soil organisms, carbon mineralization, wood decomposition, nitrification, denitrification, carbon fixation, nitrogen fixation and methanotrophy, could be basically performed by the two SGM. In general, the SGM should possess common soil capabilities according to bacterial and fungal analyses, but there are numerous fungi of unknown function that need be addressed in the future. Meanwhile, these results improve our understanding of the correlation between the environmental factors and the microbiome, and provide basic guidance for management and research on SGM in the future.