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Particulate organic matter (POM) is a key component of soil organic matter (SOM), which is easily biodegradable and rich in organic carbon (OC) and heavy metals. However, the characteristics of C mineralization and the releases of cadmium (Cd) and zinc (Zn) during POM mineralization are still poorly understood. In the present study, a 90-day incubation experiment was conducted to study the releases of CO2-C and of Cd/Zn during POM mineralization with and without organic acids amendment. The results showed that 16.6%-26.6% OC, 17.0%-29.1% of Cd and 5.09%-14.3% Zn were stored in 2000–53 µm POM size fractions. Comparing with one-time amendment, frequent organic acids amendment caused 76.4%-83.7% decreases in C priming effects. The total amounts of CO2-C emissions in POM size fractions were lower in soil with high pollution level than with low pollution level, and lower in 250–53 µm POM size fractions than in 2000–250 µm POM size fractions, respectively. The two-compartment first-order kinetic model can better fit the CO2-C mineralization process, and organic acids amendment resulting in increase in mean residence time of labile C. After 90-day incubation, 8.58%-26.5% Cd and 10.38%-38.1% Zn in 2000–53 µm POM size fractions discharged into other phrases, and frequent organic acids amendment resulted more Cd/Zn release than that by one-time amendment in soil with high pollution level. Overall, frequent organic acids amendment facilitated C mineralization and Cd/Zn release of POM in comparison with one-time organic acids amendment in soil with high pollution level. [ABSTRACT FROM AUTHOR]

The input of exogenous organic matter could affect the transformation of soil carbon (C) and nitrogen (N), and their C- and N-priming effects (CPE and NPE) play a key role in the balance of soil C and N. However, little is known about how the interaction effect between straw and straw biochar regulates CPE and NPE. Therefore, we conducted a 90-day incubation experiment, which included five treatments: no straw and straw biochar (CK), 1.5% straw (S), 0.53% straw biochar (B), 1.5% straw + 0.53% straw biochar (SB), and 1.5% straw + 1.06% straw biochar (SB1). Our findings revealed that cumulative soil CO2 emissions were increased by 95.52–216.53% through the short-term input of exogenous organic matter input; however, this trend gradually weakened with decreasing dissolved organic C (DOC) content. The cumulative NPE generated by the addition of exogenous organic matter was much smaller than the cumulative CPE. Under the B and S treatments, the cumulative CPE and NPE were negative throughout the entire incubation period. The SB treatment remarkably boosted the microbial biomass nitrogen (MBN) content; however, the SB1 treatment was more effective in inhibiting soil C and N mineralization processes than SB treatment. Moreover, the cumulative CPE and NPE were mainly regulated by N. We conclude that the combination of straw and straw biochar preferentially stimulated soil C mineralization, but that this effect decreased with time, which may be due to the consumption of labile DOC caused by the initial positive CPE, while soil N mineralization had a lag effect. [ABSTRACT FROM AUTHOR]

Legume crops in rice cultivation are typically rotated and incorporated into the soil as green manure to improve soil fertility. Biochar has recently been co-incorporated with green manure to simultaneously stimulate soil organic carbon (SOC) mineralization and increase carbon (C) sequestration. However, few studies examine the effects of the co-incorporation of biochar and green manure on C cycling and the underlying microbial mechanisms in paddy fields. In this study, the effects of the co-incorporation of green manure and biochar on C mineralization, dissolved organic carbon (DOC) characteristics, and microbial community structures were investigated. A pot study was conducted with three treatments: inorganic NPK (NPK), inorganic NPK + green manure (GM), and inorganic NPK+green manure + biochar (GMC). Organic amendments significantly increased cumulative C mineralization, with amounts in the order GMC (3,434 mg⋅kg-1)> GM (2,934 mg⋅kg-1) > NPK (2,592 mg⋅kg-1). Fertilizer treatments had similar effects on DOC concentrations, with amounts in the order GMC (279 mg⋅kg-1) > GM (255 mg⋅kg-1) > NPK (193 mg⋅kg-1). According to fluorescence spectra, the highest microbial humic acid-like fraction and biological index were also in GMC. Co-incorporation of green manure and biochar shifted the composition of bacterial and fungal communities but more importantly, increased fungal network complexity and decreased bacterial network complexity. The increase in fungal network complexity with the increase in DOC concentrations and microbially derived components was the dominant factor in promoting C mineralization. Overall, this study reveals the underlying biochemical mechanism, the interaction between DOC and fungal network of C cycling in paddy soil under the co-incorporation of green manure and biochar management, and provides fundamental knowledge for exploring effective approaches to improve soil fertility and health in the future. [ABSTRACT FROM AUTHOR]

[Display omitted] • A new model for exogenous organic matter in soil is developed. • Two digestate incubations in soil were conducted and used as calibration datasets. • The model simulates accurately the main processes observed in soil. As its use in agriculture grows, the fate of digestate in soil raises concerns on many different levels. In particular, the degradability of its organic matter when spread on soil is still an ongoing topic. In an effort to better understand the processes and dynamics of digestate soil incubation, C and N mineralization kinetics obtained in 358 days long laboratory incubations during decomposition of digestates were simulated using a dynamic model. The model includes twelve compartments related through processes including 18 parameters. The main novelty of this model is the use of accessibility-related variables to describe the fate of exogenous organic matter in soil, thus enabling a detailed understanding of its outcome in soil. Model calibration on cattle manure digestate incubation resulted in the estimation of parameter values. The newly calibrated model was then tested on an energy crop digestate incubation experiment. The model was able to reproduce accurately the experimental behavior of most variables. [ABSTRACT FROM AUTHOR]

Soil carbon (C) and nitrogen (N) mineralization rates are critical indicators of ecosystem functioning in agricultural land. However, the effects of agricultural land use on the interactions between soil C and N mineralization at different soil depths, especially in tropical regions, are poorly understood. Here, a longan orchard (LO) was converted to a conventional tea plantation (CTP) and an organic tea plantation (OTP) in the tropical region of China, and the responses of fungal and bacterial communities to these changes were assessed. The characteristics of the microbial communities, enzyme activities, and N and C mineralization rates were evaluated in response to the changes in land use. It was found that LO and OTP had faster N and C mineralization rates than CTP in surface soil. However, in subsurface soil, LO and OTP showed a faster C mineralization rate and a slower N mineralization rate than CTP. Structural equation modeling revealed that pH and C/N were the most crucial factors affecting N and C mineralization rates in surface soil. In contrast,soil bacterial and fungal community structures were the principal drivers of both the C and N mineralization in subsurface soil. Although soil C and net N mineralization were positively correlated in surface soil, this was not seen in subsurface soil. Collectively, this study demonstrated that differential drivers and their effects on the interactions between soil C and N mineralization at different soil depths should be considered for more accurate prediction of soil C and N dynamics under land-use changes. [Display omitted] • Soil C and N mineralization were positively correlated in surface soil, but not in subsurface soil. • Bacterial and fungal communities' response to agriculture LUC depended on soil depth. • Abiotic soil factors primarily controlled C and N mineralization rates in surface soil. • Soil microbial community predominantly regulated C and N mineralization in subsurface soil. • The decoupling of C min and N min is attributed to the lower level of C/N in subsurface soil. [ABSTRACT FROM AUTHOR]

Earthworms are pivotal in shaping soil ecological processes through their bioturbation activity and organic matter consumption. Earthworm species are known to have different impacts on soil structure, but only a small number of species have been studied so far, and few studies have examined how earthworms simultaneously affect soil functions. Here, we measured the impact of different earthworm species on soil structure (bioturbation function), carbon (C) and nitrogen (N) dynamics and the microbial community (organic matter transformation function), while exploring the links between these functions, across distinct soil compartments (surface casts, below-ground drilosphere, and bulk soil). Six earthworm species (Lumbricus terrestris , Allolobophora chlorotica , Octolasion cyaneum, Octodrilus complanatus , Aporrectodea caliginosa meridionalis and Microscolex dubius) of different ecological categories and functional groups were incubated in soil cores with soil and alfalfa litter for 6 weeks. Our results on the bioturbation function illustrated a great diversity of behaviors and confirmed the relevance of a functional classification based on bioturbation metrics. The main microbial hotspots were surface casts, whose characteristics allowed to distinguish two groups of species. Octod. complanatus, L. terrestris and M. dubius induced high humidity (respectively, +57, +48, +74%), high C (respectively, 19.9, 24.8, 33.2 g kg⁻1 dry soil) and N (respectively, 2, 2.3, 3.2 g kg⁻1 dry soil) content and microbial community selection, promoting C and N mineralization. The three other species had a lower impact. The below-ground drilosphere only showed specific characteristics in the case of L. terrestris. The effects of the studied species on the organic matter transformation function did not align with their bioturbation activities nor with their ecological category. These findings show that the contribution of earthworms to C and N turnover is only partially dependent on their bioturbation effects and suggest the usefulness of developing distinct functional groups based on the specific soil functions under consideration. [Display omitted] • Earthworm effects on organic matter and bioturbation functions did not align. • Surface casts were the main microbial hotspots compared to below-ground drilosphere. • Microscolex dubius showed weak bioturbation but strong effects on C and N. • Only Lumbricus terrestris modified its below-ground drilosphere. [ABSTRACT FROM AUTHOR]

Purpose: In many ecosystems, the identity of the dominant plant is changing because of global change. If the new dominant species has different litter and root traits than the one it replaces, it is likely to have an influence on soil microbial communities and the functions they perform. We used a grass-encroached heathland, where dwarf shrubs are replaced by grasses with different ecological traits, as a case study to explore this question. We hypothesized that grass colonization of heathland would improve litter quality, which would favor soil copiotroph microbes and increase C mineralization rate. Methods: We established a 13-plot field observatory spanning across a 0-100% gradient of grass cover percentage. In each plot, we characterized plant, fungal and bacterial communities, using a combination of ARISA (taxonomic diversity), metabarcoding plus hierarchical modelling of species communities (community structure), FDA assay (metabolic activity) and Biolog ecoplates (functional diversity and rate of C mineralization). Results: Our results show that microbial taxonomic and functional diversities are not affected by grass colonization. Microbial communities were also similar at high phylogenetic level, including for ericoid mycorrhizas and typical oligo- and copiotrophic species. At a finer phylogenetic level, some abundant extremophilic OTUs (e.g Acidothermus bacteria) were progressively replaced by fungal black yeasts. Functional response of microbial communities was more obvious. The C mineralization potential significantly increased across the grass gradient. Conclusion: Change in dominant plant traits may induce drastic functional changes in microbial communities despite having only a very minor effect on their diversity or structure. [ABSTRACT FROM AUTHOR]

Due to the repeated applications of pesticides, the amount of the pesticides and their products by decomposition may accumulate in the soil ecosystems which are affected by abiotic and biotic factors. Soil microorganisms are the important players that are able to decompose and utilize these chemical waste materials as energy sources and regulate them in the cycling in the soil environment. One of the important insecticides for the control of insect pests including aphids is spirotetramat which can provide protection to plant roots from the attack of insects when it was sprayed on the crops. However, effects of high concentrations of spirotetramat on soil microbial respiration under different soil water contents are unknown. Recommended field dose (RFD) and its 5 (RFD × 5) and 10 (RFD × 10) folds of spirotetramat were mixed with a clay soil; these mixtures were humidified at 50% (50FC), 75% (75FC), and 100% (100FC) of field capacity and then incubated at 28 °C for 21 days. At the end of the incubation period, (1) in general, soil microbial respiration was significantly increased as soil moisture increased in all treatments (50FC < 75FC < 100FC, P < 0.05); (2) all concentrations of spirotetramat significantly decreased the microbial respiration under 100FC (P < 0.05); (3) only RFD × 5 significantly reduced this activity under 75FC (P < 0.05); (4) no significant differences between control and treatments were found under 50FC. In conclusion, high concentrations of spirotetramat insecticide had low toxic effects on soil microbial respiration while the soil moisture regulated the toxicity effects of this insecticide. [ABSTRACT FROM AUTHOR]

Drying-wetting cycles influence both soil organic matter (SOM) decomposition and rhizosphere processes. Rhizosphere processes also affect SOM decomposition through rhizosphere priming. However, little is known about how drying-wetting cycles regulate SOM decomposition with rhizosphere priming, because most previous studies incubated root-free soils and omitted the rhizosphere effect. To investigate the effect of drying-wetting cycles on SOM decomposition in the presence of plants, we grew sunflower (Helianthus annuus) and soybean (Glycine max) in a sandy loam soil under the treatments of either constant moisture or 12 drying-wetting cycles, and used a continuous 13C-labeling method to partition soil respiration into rhizosphere respiration and SOM decomposition. We found that compared to the constantly-moist treatment, the severe drying-wetting cycles in soils planted with sunflower significantly reduced shoot biomass (32%), root biomass (52%), rhizosphere respiration (29%), and SOM decomposition (22%), while the moderate drying-wetting cycles in soils planted with soybean did not significantly affect these variables. Moreover, SOM decomposition rates in the planted treatment subjected to constantly-moist or drying-wetting conditions were significantly higher compared with the constantly-moist unplanted treatment, indicating a positive rhizosphere priming effect under both soil moisture regimes. However, drying-wetting reduced the rhizosphere priming of sunflower (69% versus 33%) likely due to lower plant biomass and rhizodeposition, but produced similar rhizosphere priming of soybean (82% versus 85%). Overall, drying-wetting cycles significantly modulated rhizosphere respiration and SOM decomposition, with the magnitude depending on soil drying intensity and plant growth performance. © 2013.

Drying-wetting cycles influence both soil organic matter (SOM) decomposition and rhizosphere processes. Rhizosphere processes also affect SOM decomposition through rhizosphere priming. However, little is known about how drying-wetting cycles regulate SOM decomposition with rhizosphere priming, because most previous studies incubated root-free soils and omitted the rhizosphere effect. To investigate the effect of drying-wetting cycles on SOM decomposition in the presence of plants, we grew sunflower (Helianthus annuus) and soybean (Glycine max) in a sandy loam soil under the treatments of either constant moisture or 12 drying-wetting cycles, and used a continuous 13C-labeling method to partition soil respiration into rhizosphere respiration and SOM decomposition. We found that compared to the constantly-moist treatment, the severe drying-wetting cycles in soils planted with sunflower significantly reduced shoot biomass (32%), root biomass (52%), rhizosphere respiration (29%), and SOM decomposition (22%), while the moderate drying-wetting cycles in soils planted with soybean did not significantly affect these variables. Moreover, SOM decomposition rates in the planted treatment subjected to constantly-moist or drying-wetting conditions were significantly higher compared with the constantly-moist unplanted treatment, indicating a positive rhizosphere priming effect under both soil moisture regimes. However, drying-wetting reduced the rhizosphere priming of sunflower (69% versus 33%) likely due to lower plant biomass and rhizodeposition, but produced similar rhizosphere priming of soybean (82% versus 85%). Overall, drying-wetting cycles significantly modulated rhizosphere respiration and SOM decomposition, with the magnitude depending on soil drying intensity and plant growth performance. © 2013.

Aims: As woody plants encroach into grassland ecosystems, we expect altered plant-soil interactions to change the microbial processes that affect soil carbon storage and nutrient cycling. Specifically, this research aimed to address how (1) soil chemistry, (2) microbial nutrient demand, and (3) the rate and source of potential soil C mineralization vary spatially under clonal woody shrubs of varying size within a mesic grassland. Methods: We collected soil samples from the center, the midpoint between the center and edge, the edge, and the shrub-grass ecotone of multiple Cornus drummondii shrubs across a shrub-size gradient in infrequently burned tallgrass prairie. Results: Total soil carbon and nitrogen increased with shrub size at every sampling location but the edge. Microbial demand for nitrogen also increased as shrubs increased in size. Across all shrub sizes and sampling locations, potential soil carbon mineralization rates were higher when microbes broke down proportionally more shrub-derived (C3) organic matter than grass-derived (C4) organic matter. Conclusions: Our results suggest that the spatio-temporal context of woody encroachment is critical for understanding its impact on belowground microbial processes. In this ecosystem, a longer period of occupancy by woody plants increases potentially mineralizable soil carbon. [ABSTRACT FROM AUTHOR]

Biochar is a chemically recalcitrant carbon-rich solid material used in soil for its potential to improve soil quality and sequester carbon. While the rate of application has implications for soil carbon dioxide (CO2) emission and the overall benefits of biochar, its effects are yet to be fully understood. To evaluate the effect of application rates of rice husk biochar on CO2 emissions, 91-day field experiments were conducted on three soil types (Anthraquic Ustorthent, Grossarenic Kandiustalf, and Ustic Quartzipsamment) in the southern Guinea Savannah of Nigeria, using three biochar application rates of 5, 15 and 25 t h−1, and control.A two-way ANOVA showed that cumulative CO2 emissions were significantly (p < 0.01) different between soil types and treatments, and soil type/treatment interactions were also significant at p = 0.05. The highest cumulative CO2–C emission of 2.77g/m2 was recorded in the Grossarenic Kandiustalf, while the least value of 2.11g/m2 was recorded in the Ustic Quartzipsamment. CO2 emission increased with increasing biochar application rates, with the highest (3.06 CO2–C g/m2) value recorded at 25 t/ha compared to 2.78 g/m2 and 1.52 g/m2 values recorded for 5 t/ha and control treatments respectively. While CO2 emissions increased with biochar application rate however, the percentage of biochar-C mineralized was higher at lower biochar rates, and differences were significant at p = 0.01. While 0.63 % of biochar C was mineralized under 5 t/ha biochar treatment, 0.15 % was recorded for 25 t/ha treatment. Factors that had significant correlation with CO2–C emission in the soils were biochar addition rate, soil pH, N, P, Ca, Mg and K. At day 91, there were no significant differences in CO2 emissions between amended treatments and control, and only a small percentage (

ABSTRACT Maintaining stability of ecosystem functions in the face of global change calls for a better understanding regulatory factors of functionally specialized microbial groups and their population response to disturbance. In this study, we explored this issue by collecting soils from 54 managed ecosystems in China and conducting a microcosm experiment to link disturbance, elemental stoichiometry, and genetic resistance. Soil carbon:nitrogen:phosphorus (C:N:P) stoichiometry imparted a greater effect on the abundance of microbial groups associated with main C, N, and P biogeochemical processes in comparison with mean annual temperature and precipitation. Nitrogen cycling genes, including bacterial amoA-b, nirS, narG, and norB, exhibited the highest genetic resistance to N deposition. The amoA-a and nosZ genes exhibited the highest resistance to warming and drying-wetting cycles, respectively. Soil total C, N, and P contents and their ratios had a strong direct effect on the genetic resistance of microbial groups, which was dependent on mean annual temperature and precipitation. Specifically, soil C/P ratio was the main predictor of N cycling genetic resistance to N deposition. Soil total C and N contents and their ratios were the main predictors of P cycling genetic resistance to N deposition, warming, and drying-wetting. Overall, our work highlights the importance of soil stoichiometric balance for maintaining the ability of ecosystem functions to withstand global change. IMPORTANCE To be effective in predicting future stability of soil functions in the context of various external disturbances, it is necessary to follow the effects of global change on functionally specialized microbes related to C and nutrient cycling. Our study represents an exploratory effort to couple the stoichiometric drivers to microbial populations related with main C, N, and P cycling and their resistances to global change. The abundance of microbial groups involved in cellulose, starch, and xylan degradation, nitrification, N fixation, denitrification, organic P mineralization, and inorganic P dissolution showed a high stoichiometry dependency. Resistance of these microbial populations to global change could be predicted by soil C:N:P stoichiometry. Our work highlights that stoichiometric balance in soil C and nutrients is instrumental in maintaining the stability and adaptability of ecosystem functions under global change.

Carbon (C) mineralization of crop residues is an important process occurring in soil which is helpful in predicting CO2 emission to the atmosphere and nutrient availability to plants. A laboratory experiment was conducted in which C mineralization of residues of rice (Oryza sativa), wheat (Triticum aestivum), maize (Zea mays), mungbean (Vigna radiata) and their mixtures was applied to the soil surface or incorporated into an Alfisols from Northwest India. C mineralization was significantly affected by residue placement and type and their interactions. Rice residue had a higher decomposition rate (k = 0.121 and 0.076 day−1) than wheat (0.073 and 0.042 day−1) and maize residues (0.041 day−1) irrespective of placements. Higher decomposition rates of rice and wheat were observed when placed on soil surface than incorporated in the soils. Additive effects of the contribution of each residue type to C mineralization of the residue mixture were observed. When mungbean residue was added to the rice/wheat or maize/wheat mixture, decomposition of the residue mixture was enhanced. Crop residues with low N and high C/N ratio such as maize, wheat, rice and their mixtures can be applied on the soil surface for faster C and N mineralization, thereby helping to manage high volumes of residues under conservation agriculture-based practices in northwest India.

Interactions between tephra deposits from volcanic eruptions and peatland carbon (C) dynamics are poorly understood despite the significant extent of peatlands influenced by tephra worldwide. Tephra falls can affect peat accumulation within a radius of at least 1,000 km. In Iceland, volcanic activity is amongst the highest in the world and it might even increase due to pressure release on subglacial volcanoes. A potent combination of sparse vegetation, low cohesion of Andosols, and frequent strong winds, facilitates the regular input of mineral aeolian material from eroded areas into peatlands in Iceland, in addition to tephra deposits. We present results of a study on the impact of a major tephra deposit, the Hekla 4 tephra, on C dynamics in Icelandic peatlands. We investigated three sites at differing distances from the active volcanic zones and major erosion areas in the interior of the country. A combination of variables was applied, including laboratory C mineralization at 5, 15 and 25°C and C structure obtained by solid‐state 13C NMR spectroscopy. Tephra deposits seem to affect C dynamics. Differences in C mineralization can only be partially explained by C structure. The C mineralization from soils with conspicuously similar C structure differs by a factor of up to 2.7. Temperature sensitivity of decomposition after the tephra deposition increases by a factor of up to 2.2. Changes in inorganic matter and the ratio of soil organic matter to soil organic carbon by a factor of up to 1.3 and 1.4, respectively, were also observed. [ABSTRACT FROM AUTHOR]

Nitrate (NO 3 --N) accumulation in soils resulting from excessive nitrogen (N) fertilization increases risks of N loss to the environment. Microbial NO 3 --N immobilization (I NO3) can be stimulated by adding high-organic carbon (C) materials to soils and has potential to control N loss from agricultural soils during periods of NO 3 --N accumulation. It is therefore important to screen for such organic materials that show a rapid and high capacity of I NO3. The C/N ratio of organic materials is considered a primary factor controlling soil I NO3 , but this is challenged for high-organic C soil amendments that have similar C/N ratios but contain components with very different microbial degradability. Our objective was to identify better predictors of the I NO3 potential of high organic C materials with comparable C/N ratios. Using a 15N-tracing laboratory experiment on one nitrate-rich agricultural soil with and without 11 types of organic C materials, we observed that those with similar C/N ratios (>18) increased the I NO3 to varying degrees. Once organic amendments exceed a C/N ratio of 18, this ratio may no longer be an ideal index for estimating rapid I NO3 potential. We provide evidence that the C mineralization of high-organic C soil amendments, determined as CO 2 emission over 12 days, more accurately predicts the potential for rapid I NO3 in soil. [Display omitted] • High-organic C materials with similar C/N differ in microbial nitrate immobilization (I NO3). • C/N was a poor predictor of I NO3 for organic materials exceeding the threshold of 18. • CO 2 -derived C mineralization of these materials was a better predictor of the rapid I NO3. [ABSTRACT FROM AUTHOR]

• Drying-rewetting had no effect on soil respiration when straw was absent. • Drying-rewetting had a strong legacy effect on SOM mineralization when straw was added. • Drying-rewetting cycles reduced cumulative straw decomposition. • Drying-rewetting effect on PE diminished with the increase in the number of drying-rewetting cycles. Soil moisture serves as a pivotal environmental variable that governs the cycling of soil carbon (C). Although numerous studies have been conducted to evaluate the impact of drying-rewetting cycles on soil organic matter (SOM) mineralization, the dynamic changes in SOM priming effect (PE, i.e. the change in SOM mineralization after the addition of an exogenous substrate) under frequent drying-rewetting cycles remain unknown. Here, we conducted a 209-day incubation experiment utilizing 13C-labeled maize (Zea mays L.) straw to investigate how repeated drying-rewetting events influence straw decomposition, SOM mineralization, PE, and soil net sequestration of straw-C. The experimental design involved two contrasting soil moisture conditions (constant vs. varying water content) with or without maize straw amendment. Results showed that, in the absence of maize straws, drying-rewetting cycling did not significantly alter the cumulative SOM mineralization throughout the incubation period. Conversely, in the presence of maize straws, the cumulative decomposition of straws under drying-rewetting cycles was diminished by 9.8% compared to the constant water conditions. Moreover, a notable increase of the cumulative PE by 19.3% under recurrent drying-rewetting events resulted in a substantial reduction of soil net C sequestration of straw-C (straw-derived C incorporated into the soil minus the C loss primed by straw) by 22.3% compared to the constant water conditions after 209-day incubation, suggesting that frequent drying-rewetting might diminish the function of soil as a C sink. Overall, drying-rewetting cycles generally decelerated straw decomposition and reduced the recovery of straw-C in microbial biomass C and soil matrix, indicating that enhanced frequency and intensity of drying-rewetting cycles in future climate scenarios may have detrimental effects on soil C sequestration. [ABSTRACT FROM AUTHOR]

While litter traits have been used for decades to predict decomposition rates through the Leaf Economics Spectrum (LES) acquisitive to conservative trait lens, litter trait and litter mixture effects on soil carbon (C) priming effects (PE) is less known. To assess whether the LES can predict soil C PE during the decomposition of litter mixtures from complex ecosystems, a 99-day incubation experiment was conducted. The experiment involved soil and leaf litter from three Canadian riparian land uses (grasslands, deciduous agroforests, and coniferous agroforests), incubated as single plant species, and as plant species mixtures in their natural proportions. Natural abundance δ13C-isotopic analysis was used to assess the proportion of CO 2 derived from leaf litter versus soil C mineralization at initial (0–21 days, stage I) and later (22–99 days, stage II) stages of decomposition. Single species positions on the LES mirrored litter-C mineralization dynamics, yet PE emissions remained harder to predict with LES traits. Nonetheless, higher PE emissions relative to litter-C mineralization were observed with litter from LES species expressing conservative traits compared to LES species expressing acquisitive traits. Leaf litter mixtures from both agroforests, expressing high leaf litter trait functional dissimilarity, resulted in synergistic, non-additive effects on soil PE. These findings contribute to our understanding of the effects of leaf litter functional traits and trait mixing on soil PE, highlighting that mixed-species litter decomposition can lead to non-additive effects on soil C dynamics in forested riparian ecosystems. • Leaf traits along the Leaf Economics Spectrum predict litter carbon mineralization. • Leaf traits do not predict soil carbon priming. • High trait dissimilarity resulted in synergistic, non-additive effects on soil PE. • Soil priming varies across diversified riparian land uses. [ABSTRACT FROM AUTHOR]

The interactive effect of biochar, cattle manure and nitrogen (N) fertilizer on the dynamics of carbon (C) mineralization and stabilization was investigated in a sandy soil amended with three sole biochar (0, 20 or 40 t ha−1) or manure (0, 13 or 26 t ha−1) and four combined biochar-manure levels (20 or 40 t ha−1 biochar plus 13 or 26 t ha−1 manure) with or without N fertilizer (0 or 90 kg ha−1) and CO2-C evolution measured over 54-d incubation period. Biochar application, solely or combined with manure resulted in lower applied C mineralized (ACM), indicating C sequestration in the soils. Negative attributable effect (AE) of co-application of biochar and manure on C mineralization was observed relative to the sole treatments. Both ACM and AE were negatively correlated with C/N ratio and mineral N content of the soil-mixtures (r ≥ – 0.573; p ≤ 0.01), indicating microbial N limitation. The double first-order exponential model described CO2-C efflux very well and indicated that ≥94% of C applied was apportioned to stable C pools with slower mineralization rate constant and longer half-life. Cumulative C mineralized and modeled C pools were positively correlated with each other (r ≥ 0.853; p ≤ 0.001) and with readily oxidizable C of soil-amendment mixtures (r ≥ 0.861; p ≤ 0.001). The results suggested that co-application of biochar and manure can promote initial rapid mineralization to release plant nutrients but sequester larger amounts of applied C in refractive C pool, resulting in larger C sequestration in sandy soils. [ABSTRACT FROM AUTHOR]

Abstract The development of soil sustainability is linked to the improved management of soil biota, such as earthworms, and crop residues to improve soil physical structure, enhance microbial activities, and increase nutrient cycling. This study examined the impacts of maize residue (65.8C/N ratio, dry biomass 0.75 kg m−2) incorporation and earthworms (70 g Metaphire guillelmi m−2) on the resistance and resilience of soil C and N cycling to experimentally applied stresses. Field treatments were maize residue incorporation, maize residue incorporation with earthworm addition, and an unamended control. Resistance and resilience of C mineralization, ammonia oxidation, and potential denitrification were investigated over 28 days following a persistent stress of Cu (1 mg Cu soil g−1) or a transient heat stress (50 °C for 16 h). The results indicated that C mineralization was more resistant and resilient than ammonia oxidation and denitrification to either a persistent Cu or a transient heat stress. The application of maize residues significantly increased soil microbial biomass, C mineralization, ammonia oxidation and potential denitrification compared with the unamended control. Maize residues significantly improved the resistance and resilience of N processes to Cu and heat stress. The presence of earthworms significantly increased potential denitrification but had limited positive effect on functional resistance and resilience. This study suggested crop residue incorporation would strongly increase soil functional resistance and resilience to persistent and transient stresses, and thus could be a useful agricultural practice to improve soil ecosystem sustainability. Highlights • C cycling is more resistant and resilient to Cu and heat than N cycling • Resistance and resilience are primarily improved by the addition of crop residues • C and N processes can recover from heat rather than Cu [ABSTRACT FROM AUTHOR]

Epichloë coenophiala forms aboveground symbiotic relationships with tall fescue (Festuca arundinacea) and provides the host with better fitness. This study investigated the effects of endophyte symbiosis on carbon mineralization in soil. Two soils were amended with endophyte-infected (E+) or endophyte-free (E−) residues of two tall fescue genotypes. At the end of the experiment, CO 2 evolution rates were monitored to quantify the mineralized carbon. The indices of carbon mineralization were significantly greater (LSD, P < 0.05) in the E−compared to E+ plant residue treated soils. Cellulose, hemicellulose, lignin contents, C:N and lignin:N ratios were significantly greater (LSD, P < 0.05) in soils with the E+ residues than in those with E− residues. Additionally, the E+ plant residues consistently contained significantly less N (LSD, P < 0.05). Overall, it is concluded that grass-endophyte symbiosis results in the production of less biodegradable plant residues, in turn reducing the residue biodegradability and promoting greater C accumulation in the soils. • Endophyte symbiosis increases cellulose, hemicellulose and lignin contents. • Endophyte-infected plants possess lower N and higher C:N and lignin:N ratios. • Endophyte-infected tall fescue plants are less biodegradable. • Degradation kinetic parameters were lower in endophyte-infected plants. [ABSTRACT FROM AUTHOR]

Fruit orchards are a major part of agricultural production, and planting cover crops (CCs) in the row middles of these agroecosystems can increase soil nutrient availability. However, it is largely unknown how different mixtures of CCs may impact soil carbon (C) and nitrogen (N) concentrations, greenhouse gas emissions (GHG), and the soil microbiome at different soil depths, which is important for understanding the contribution of CCs to these agroecosystems. We examined how CC composition (legumes and non-legumes vs. non-legumes only compared to a grower-standard treatment) affects soil properties, nitrification rates and gene abundances, N and C mineralization rates, denitrification gene abundances, and emissions of nitrous oxide (N 2 O) and dinitrogen (N 2) at different soil depths (0- to 10-cm, 10- to 20-cm, and 20- to 30-cm soil layers) in the row middles of a Florida (USA) commercial citrus orchard after 30 months of CC treatment. We found that CC impacts on soil N and C concentrations and mineralization rates, emissions of N 2 O and N 2 , and the abundance of N-cycling genes mainly occurred in the top 0- to 10-cm soil layer whereas differences in these variables in deeper layers were not statistically significant. The combined use of legumes and non-legumes led to significantly greater soil NH 4 + concentrations, net nitrification and N mineralization rates, and lower N 2 O emissions. Lower N 2 O emissions with legumes were linked to a greater abundance of N 2 O reducers vs. N 2 O producers compared to non-legumes alone and the grower-standard treatment in the topsoil layer. This study shows that CC impacts on soil nutrient cycling and microbial communities occur primarily in the topsoil of citrus orchards and that planting diverse CC mixtures is important to enhance soil-microbe interactions to diminish GHGs. • Cover crops primarily impacted soil nutrient cycling in the 0- to 10-cm soil layer. • Abundance of N-cycling genes and gas emissions impacted only in the top soil. • Legume + non-legume cover crops reduced N 2 O emissions more than non-legumes. • Legume + non-legume cover crops increased net nitrification and N mineralization. • Soil moisture and cover crop composition impacted N 2 O production and reduction. [ABSTRACT FROM AUTHOR]

Mineral nitrogen (N) availability to heterotrophic micro-organisms is known to impact organic matter (OM) decomposition. Different pathways determining the N accessibility depend to a large extent on soil structure. Contact between soil mineral and OM substrate particles can facilitate N transport toward decomposition hot spots. However, the impact of soil structure on N availability to microbes and thus heterotrophic microbial activity and community structure is not yet fully understood. We hypothesized that carbon mineralization (Cmin) from low-N substrate would be stimulated by increased N availability caused by closer contact with soil particles or by a higher moisture level, enhancing potential for N-diffusion. Under opposite conditions retarded heterotrophic activity and a dominance of fungi were expected. A 128-days incubation experiment with CO2 emission monitoring from artificially reconstructed miniature soil cores with contrasting soil structures, viz. high or low degree of contact between soil particles, was conducted to study impacts on heterotrophic activity. The soil cores were subjected to different water filled pore space percentages (25 or 50% WFPS) and amended with either easily degradable OM high in N (grass) or more resistant OM low in N (sawdust). X-ray μCT image processing allowed to quantify the pore space in 350 μm around OM substrates, i.e., the microbial habitat of involved decomposers. A lower local porosity surrounding sawdust particles in soils with stonger contact was confirmed, at least at 25% WFPS. Mineral N addition to sawdust amended soils with small particle contact at 25% WFPS resulted in a stimulated respiration. Cmin in the latter soils was lower than in case of high particle contact. This was not observed for grass substrate particles or at 50% WFPS. The interactive effect of substrate type and soil structure suggests that the latter controls Cmin through mediation of N diffusion and in turn N availability. Phospholipid fatty acid did not reveal promotion of fungal over bacterial biomarkers in treatments with N-limited substrate decomposition. Combining X-ray μCT with tailoring soil structure allows for more reliable investigation of effects on the soil microbial community, because as also found here, the established soil pore network structure can strongly deviate from the intended one.

Carbon (C) mineralization of crop residues is an important process occurring in soil which is helpful in predicting CO2 emission to the atmosphere and nutrient availability to plants. A laboratory experiment was conducted in which C mineralization of residues of rice (Oryza sativa), wheat (Triticum aestivum), maize (Zea mays), mungbean (Vigna radiata) and their mixtures was applied to the soil surface or incorporated into an Alfisols from Northwest India. C mineralization was significantly affected by residue placement and type and their interactions. Rice residue had a higher decomposition rate (k = 0.121 and 0.076 day−1) than wheat (0.073 and 0.042 day−1) and maize residues (0.041 day−1) irrespective of placements. Higher decomposition rates of rice and wheat were observed when placed on soil surface than incorporated in the soils. Additive effects of the contribution of each residue type to C mineralization of the residue mixture were observed. When mungbean residue was added to the rice/wheat or maize/wheat mixture, decomposition of the residue mixture was enhanced. Crop residues with low N and high C/N ratio such as maize, wheat, rice and their mixtures can be applied on the soil surface for faster C and N mineralization, thereby helping to manage high volumes of residues under conservation agriculture-based practices in northwest India. [ABSTRACT FROM AUTHOR]

Abstract Agro-industrial systems provide large quantities of organic wastes that could imply an important environmental risk. While manures can be easily treated by anaerobic digestion, horticultural fruit wastes generally cannot be processed alone and should be treated by co-digestion. To use organic wastes as fertilizers is fundamental to improve understanding of their impact on soil-plant systems. In this research, cattle manure, poultry litter, pig slurry and onion waste were collected. Animal manures were studied without treatment, treated by anaerobic digestion alone and in co-digestion with onion wastes. To study their effect on soil-plant systems, chemical and spectroscopic characterization of manures and their transformed products were combined with soil biological activity and growth dynamic of lettuce following wastes incorporation to the soil. Anaerobic digestion decreased the C/N ratio, whilst there was an increase in NH 4 +-N/N ratio and short-chain organic acids. The magnitude of these changes varied depending on the type of organic matter present in each material and the incorporation of onion wastes intensified them. However, the digestates presented similar structural characteristics to each other, independently of the material of origin. Digestate soil application produced a fast and short microbial stimulation (18–34 and 7–11 mg CO 2 during the first 6 h, digestates vs. rest of treatments). The digestate dosage should be done according to the content of NH 4 +-N given that the vegetal growth is related to it. Soils amended with digestates showed less CO 2 emission than soils amended with manures improving overall C balance. Graphical abstract Unlabelled Image Highlights • Anaerobic digestates showed similar organic structural characteristics. • Digestate soil application improved the overall C balance with respect to manures. • Co-digestion with onion wastes improved nutrient availability for lettuce plants. • The larger part of yield is the result of the initial content of inorganic nitrogen. • The digestate dosage should be done according to the content of NH 4 +-N. [ABSTRACT FROM AUTHOR]

The adoption of conservation agriculture (CA) in the intensive triple-cropping, rice-based systems of the Eastern Gangetic Plain (EGP) alters the dynamics of carbon (C) in the soil, but the nature of these changes is poorly understood. Our aim was to determine whether CA in these systems involving non-puddled transplanting of wetland rice and strip planting of dryland crops plus increased residue retention would increase the C storage in soils relative to conventional crop establishment practices. Long-term field experiments were studied in two locations of northwestern Bangladesh to determine C turnover as well as examining C cycling under three levels of soil disturbance (conventional tillage (CT), strip planting (SP) and bed planting (BP)) in combination with low residue (straw) retention (LR, the current practice) and increased residue retention (HR) in Calcareous Brown Floodplain soil (Alipur) and Grey Terrace soil (Digram). The total nitrogen (N), organic C, microbial biomass C (MBC) and water-soluble C (WSC) values were measured in soil samples from 0 to 10 cm depth collected at different stages during the growth of the 13th and 14th crops at Alipur and the 12th and 13th crops at Digram since the treatments commenced. At each location, SP and BP with either LR or HR retained more soil organic C (0–10 cm) from C inputs than CT with HR and LR. In general, the CO 2 emissions relative to the stored soil organic C in the soils (0–10 cm) under SP with LR and HR were approximately 13 to 59% lower than those under CT and BP with LR and HR. The higher levels of C mineralization were associated with higher WSC contents in the soil. In contrast, the MBC contents in the HR treatments followed the order SPHR > BPHR > CTHR. Similarly, in SPLR and SPHR, the potentially mineralizable C (PMC) was higher, while the decay rate constant was lower. Increased residue retention with minimal soil disturbance practices (SP and non-puddled transplanting) after 14 crops at Alipur and 13 crops at Digram modified the C cycle by decreasing C emissions and increasing the levels of total organic C in the soil. The application of both minimal soil disturbance and increased residue retention enhanced soil organic C (0–10 cm) concentrations in the two soils under intensive rice-based cropping systems on the EGP. [ABSTRACT FROM AUTHOR]

The Arctic is the world’s largest reservoir of soil organic carbon and understanding biogeochemical cycling in this region is critical due to the potential feedbacks on climate. However, our knowledge of carbon (C) and nitrogen (N) cycling in the Arctic is incomplete, as studies have focused on plants, detritus, and microbes but largely ignored their consumers. Here we construct a comprehensive Arctic food web based on functional groups of microbes (e.g., bacteria and fungi), protozoa, and invertebrates (community hereafter referred to as the invertebrate food web) residing in the soil, on the soil surface and within the plant canopy from an area of moist acidic tundra in northern Alaska. We used an energetic food web modeling framework to estimate C flow through the food web and group-specific rates of C and N cycling. We found that 99.6% of C processed by the invertebrate food web is derived from detrital resources (aka ‘brown’ energy channel), while 0.06% comes from the consumption of live plants (aka ‘green’ energy channel). This pattern is primarily driven by fungi, fungivorous invertebrates, and their predators within the soil and surface-dwelling communities (aka the fungal energy channel). Similarly, >99% of direct invertebrate contributions to C and N cycling originate from soil- and surface-dwelling microbes and their immediate consumers. Our findings demonstrate that invertebrates from within the fungal energy channel are major drivers of C and N cycling and that changes to their structure and composition are likely to impact nutrient dynamics within tundra ecosystems. [ABSTRACT FROM AUTHOR]

Mineral nitrogen (N) availability to heterotrophic micro-organisms is known to impact organic matter (OM) decomposition. Different pathways determining the N accessibility depend to a large extent on soil structure. Contact between soil mineral and OM substrate particles can facilitate N transport toward decomposition hot spots. However, the impact of soil structure on N availability to microbes and thus heterotrophic microbial activity and community structure is not yet fully understood. We hypothesized that carbon mineralization (Cmin) from low-N substrate would be stimulated by increased N availability caused by closer contact with soil particles or by a higher moisture level, enhancing potential for N-diffusion. Under opposite conditions retarded heterotrophic activity and a dominance of fungi were expected. A 128-days incubation experiment with CO2 emission monitoring from artificially reconstructed miniature soil cores with contrasting soil structures, viz. high or low degree of contact between soil particles, was conducted to study impacts on heterotrophic activity. The soil cores were subjected to different water filled pore space percentages (25 or 50% WFPS) and amended with either easily degradable OM high in N (grass) or more resistant OM low in N (sawdust). X-ray μCT image processing allowed to quantify the pore space in 350 μm around OM substrates, i.e., the microbial habitat of involved decomposers. A lower local porosity surrounding sawdust particles in soils with stonger contact was confirmed, at least at 25% WFPS. Mineral N addition to sawdust amended soils with small particle contact at 25% WFPS resulted in a stimulated respiration. Cmin in the latter soils was lower than in case of high particle contact. This was not observed for grass substrate particles or at 50% WFPS. The interactive effect of substrate type and soil structure suggests that the latter controls Cmin through mediation of N diffusion and in turn N availability. Phospholipid fatty acid did not reveal promotion of fungal over bacterial biomarkers in treatments with N-limited substrate decomposition. Combining X-ray μCT with tailoring soil structure allows for more reliable investigation of effects on the soil microbial community, because as also found here, the established soil pore network structure can strongly deviate from the intended one. [ABSTRACT FROM AUTHOR]

Peat wetlands are of major importance for ecosystem services such as carbon storage, water regulation and maintenance of biodiversity. However, peat drainage for farming leads to CO 2 emission, soil subsidence and biodiversity losses. In the peat areas in the Netherlands, solutions are sought in reducing drainage, adapting farming to wetter soils, and converting productive dairy grasslands to less intensively managed semi-natural grasslands. Our objective was to compare the soil ecology and related ecosystem services of dairy and semi-natural grasslands on peat soils (Terric Histosols). Soil biotic and abiotic parameters were measured in twenty dairy and twenty semi-natural sites, with particular focus on (i) soil faunal diversity (ecosystem service “maintenance of biodiversity”), (ii) CO 2 emission (“climate regulation”), (iii) water infiltration (“water regulation”) and (iv) soil fertility (“grass production”). Mean soil faunal taxonomic richness per site (alpha diversity) was higher in dairy grasslands compared to semi-natural grasslands. However, the total observed number of taxa (gamma diversity) in dairy grassland was 13% lower for soil fauna and 21% lower when including plant species. Potential C mineralization rate in the topsoil – used as a proxy for CO 2 emission – was not influenced by land use but was limited by drought. Additionally, potential C mineralization depended on different C sources and microbial groups in the two grassland types. Water infiltration rate differed by a factor of five between land use types (dairy > semi-natural), and correlated with soil porosity. As expected, soil fertility was higher in dairy than in semi-natural grasslands. However, potential N mineralization was similar in dairy and semi-natural grasslands and was correlated negatively with bacterial biomass apparently indicating N immobilization, and positively with bacterial growth that depended on labile C and N in soil. Our study on peat soils shows that dairy versus semi-natural grassland use influences biodiversity, climate regulation, water regulation and (potential for) grassland production. We conclude with recommendations for land management to optimize the delivery of those ecosystem services. [ABSTRACT FROM AUTHOR]

ABSTRACT Isotopic labeling of plants is useful in tracking the fate of carbon (C) from different plant parts in a soil-plant system when these parts decompose simultaneously. Pulse labeling is a relatively simple technique and is amenable for use in the field. Therefore, we evaluated a 13CO2 pulse-labeling method to label crop plants under subtropical field conditions for simultaneous root and shoot decomposition studies. Wheat (Triticum aestivum L.), pea (Pisum sativum L.), and vetch (Vicia sativa L.) plants were grown inside polyvinyl chloride (PVC) cylinders and pulse labeled once a week for a total of 11 times. After harvest, “paired” treatments were designed by combining 13C-labeled shoots with unlabeled roots and unlabeled shoots with 13C-labeled roots, resulting in six treatments (2 combinations × 3 species), plus an unamended control treatment. The 13C enrichment of plant parts, chemical fractions, 13C recovery, and distribution in roots, shoots, and soil were determined. Soil CO2 emissions were measured continuously by the alkaline trap method for 180 days. Plant dry matter production and chemical composition were not modified by 13C labeling. The maximum level of 13C enrichment (δ13C) in plants was +495 %o in wheat, +426 %o in pea, and +378 ‰ in vetch plants. All three crops showed similar patterns of 13C distribution in the following order: shoots > roots > soil. On average, 81 to 89 % of the recovered 13C was in the shoots, 7 to 14 % was in the roots, and 2.7 to 4.3 % was in the soil. The rate of C mineralization and cumulative C mineralization were not different between “paired” treatments of the three crops, showing that the paired treatments were equally degradable. The pulse-labeling technique used under field conditions allowed for production of sufficiently labeled wheat, pea, and vetch plants. Therefore, it is a practical approach with respect to resource demand (tracer and labor costs), and it is suitable for in situ labeling.

The study of soil C dynamics and factors controlling this important soil process in rangeland ecosystems may provide an insight into understanding and evaluating changes in the global C cycle. The primary objective of this study was to quantity the effects of pasture management (i.e., grazing, controlled grazing and ungrazing) on soil C levels and mineralization in three natural rangeland sites of Chaharmahal Va Bakhtiyari province. Three range management regimes including: (a) long-term ungrazed, (b) controlled grazed and (c) free (over) grazed in close vicinity were selected at three sites including SabzKouh (protected from grazing for 18 years), Boroujen (protected from grazing for 23 years) and Sheida (protected from grazing for 2 years). Soil samples were collected from 0-15 cm depth and organic C, total N and C mineralization were measured using standard methods. Results show that SabzKouh and Sheida sites had the highest (14.6 mg g-1) and the lowest (4.80 mg g-1) soil organic C contents, respectively. Soil total N and organic C contents at SabzKouh were significantly higher when compared to other sites, probably due to more rainfall and humid climate. The effect of range management on soil C mineralization was evident at two of the three sites. Results indicate that the exclusion of grazing animals resulted in an increase in soil C mineralization at SabzKouh and Boroujen sites, probably through the addition of plant residues and animal excrements to the soil. However, ungrazed management did not improve plant cover and soil properties in Sheida area, due likely to dry climate conditions, less biomass production and the history of cultivation and agricultural uses. It is, therefore, concluded that the effect of grazing on soil C mineralization depends primarily upon the plant community and climatic conditions and also upon the type of rangeland management and even land use history involved.

Agricultural production in Malaysia has been continually growing. Most of the agricultural waste has been discarded or burnt on land; however, these agricultural wastes can serve as a feedstock for biochar production, which contributes an insignificant net amount of carbon dioxide to the atmosphere after soil incorporation. Three kinds of primary biochar were used in this study: empty fruit bunch biochar (EFB), wood biochar (WB), and rice husk biochar (RHB). EFB and WB were produced by slow pyrolysis, whereas RHB was produced by gasification. This study aimed to understand how pyrolysis technologies of native feedstocks impact the chemical characteristics and short-term soil stability of biochar. The kinetic parameters of C-mineralization suggested a tri-phasic C-mineralization process (labile, unstable, and recalcitrant carbon). The estimates indicated the existence of a very labile C-fraction in RHB with a very small decay constant K3. Fourier transform infrared spectroscopy and X-ray diffraction showed the three phases of the biochar, from the microcrystalline C of the labile fraction to the largely amorphous intermediate C of the unstable fraction, and lastly the formation of turbostratic crystallite C in the recalcitrant fraction. It has been concluded that RHB had a higher degree of aromaticity and greater stability, and therefore should be more recalcitrant to biological and chemical degradation.

The disposal of crude glycerol, the biodiesel by-product, may become an economic or environmental problem in cases where no trading of this material is possible. This study aimed at evaluating the decomposability in soil of the unpurified glycerol fraction taken after the transesterification of oil using sodium hydroxide as a catalyst. The immediate effect of glycerol incorporation was a considerable increase in soil pH. In soil samples characterized by low biological activity this pH increase did not permit microbial development although the time lag before the growth of microorganisms feeding on glycerol was shortened after the addition of a nitrogen inorganic source. On the contrary, in soils with higher organic matter content and active microbial communities, excess alkalinity was rapidly eliminated and glycerol C mineralization progressed with a relatively high rate reaching 53% of initial C added after 2.5 months of incubation when an inorganic nitrogen source was available. It is concluded that results allow for further consideration of the possibility of spreading glycerol on soil or including it in compost piles.

Conversion from agriculture to forestry is considered a measure for mitigation of atmospheric CO 2 but the impacts on soil C and N processes remain still unclear. We investigated heterotrophic respiration (R H ), specific carbon mineralization (C MIN ) and nitrogen mineralization (N MIN ) in Norway spruce ( Picea abies (Karst.) L.) and oak ( Quercus robur L.) chronosequences on former cropland by laboratory incubation. The R H was estimated as the release of C per gram soil and C MIN as the release of C per gram of soil organic matter (SOM). Seven Norway spruce stands (16–44 years), eight oak stands (4–43 years), a cropland, a 35 years old permanent pasture and a 200-year-old oak-dominated forest were sampled (0–5 cm and 5–15 cm soil layers) in early spring. The SOM content gradually increased with stand age in 0–5 cm but remained the same in the 5–15 cm soil layer. The R H in the 0–5 cm layer gradually increased with time since afforestation in both tree species while there was no change in C MIN. In 5–15 cm, neither R H nor C MIN changed significantly after afforestation, but oak stands had significantly higher R H than Norway spruce. The N MIN and nitrification in 0–5 cm significantly increased with stand age and only nitrification was higher in oak. In 5–15 cm, only N MIN in oak increased with stand age, but both N MIN and nitrification were significantly higher in oak than spruce. Cropland R H , C MIN and N MIN rates were comparable to those found within the first decades of afforestation, whereas the 200-year-old forest and the pasture generally had R H and N MIN rates similar to the older chronosequence stands. We conclude that potential R H and soil N mineralization increased with time since afforestation and were tree species specific. Soil organic C stock gains observed in this area during the first 45 years after afforestation were not driven by decreased SOM decomposability, leaving increased litter C inputs as a more likely explanation. The lower C MIN in the 200-year-old forest suggests that future studies should include older forests to assess if the stability of C and the retention of N may increase in a longer term perspective. [ABSTRACT FROM AUTHOR]

Temperature response quotient ( Q 10 ) is a critical parameter for evaluating global additional carbon (C) release with climate change. However, its value is usually derived from time span or instantaneous rate or cumulative amount of C flux, giving a very one-sided account of thermal sensitivity of C cycling. Through a 117-day laboratory incubation study, we estimated Q 10 values simultaneously with the labile (a 0 ) and recalcitrant C proportions and their rate constants, and then tested for any variances of these kinetic properties in different vegetation stands, soil horizons, aeration statuses, and thermal settings (i.e., diurnally-varying, constant low and constant high temperatures). A regularly varying temperature regime increased the exploitation of labile C resources (i.e., high a 0 ) and required longer time spans (i.e., low rate constants). The constant high temperature induced the exhaustive depletion of the labile C pool and motivated a very rapid and short-term C mineralization process. The constant low temperature treatment was characterized by the lowest a 0 but by medium rate constants because low temperature slowed the C mineralization processes but retained high level of the original C processing diversity. Therefore, a 0 and the rate constants showed discrepancies in their temperature sensitivities as revealed by pairwise comparisons of temperature regimes. Such discrepancies were also supported by pairwise comparisons of aeration statuses, forest stands and soil horizons. The Q 10 bias between C mineralization a 0 and rate constants in this laboratory experiment is attributed to the inherently distinct properties of these two parameters, as a 0 and its Q 10 are closely correlated with the sizes of the easily available C pool, while rate constants and their Q 10 variances explain the temporal scale of the same C mineralization process. Our findings suggest a combined application of a 0 and rate constants for exploring the temperature sensitivity of C mineralization in future studies. [ABSTRACT FROM AUTHOR]

Although soil Collembola are known to contribute to soil carbon (C) cycling, their contribution to the mineralization of C sources that differ in bioavailability, such as soil organic C (SOC) and leaf litter, is unknown. Stable C isotopes are often used to quantify the effects of both soil C and litter C on C mineralization. Here, C-labeled litter was used to investigate the effects of Collembola ( Folsomia candida) on the mineralization of both SOC and litter C in laboratory microcosms. The three microcosm treatments were soil alone (S); soil treated with δC-labeled litter (SL); and soil treated with δC-labeled litter and Collembola (SLC). The presence of Collembola did not significantly affect soil microbial biomass or litter mass loss and only had a small effect on CO release during the first week of the experiment, when most of the CO was derived from litter rather than from SOC. Later, during the experiment (days 21 and 63), when litter-derived labile C had been depleted and when numbers of Collembola had greatly increased, Collembola substantially increased the emission of SOC-derived CO. These results suggest that the effect of Collembola on soil organic C mineralization is negatively related to C availability. [ABSTRACT FROM AUTHOR]

Nitrogen (N)-rich vegetable crop residues left in the field may result in a high risk for N losses during autumn. Removal and conservation of these residues followed by reuse in the field could contribute to improved recycling of nutrients, but some form of processing is required to allow storage before re-application. We have compared co-ensiling, co-composting and anaerobic co-digestion as conservation and valorization options for fresh crop residues. We studied (1) the product quality and stability and (2) the short-term effects of application of these silages, composts and digestates on soil C and N mineralization and N 2 O emissions. Ensiling resulted in highly biodegradable products with a low pH (4.2-5.2) and more NH 4 + -N compared to composts. Consequently, soil incorporation of silages resulted in higher net C mineralization (up to 47% after 82 days) and microbial biomass C (up to 93 μg C g −1 soil after six weeks), and temporary N immobilization (up to 42 mg kg −1 soil). Digestates and composts led to lower C mineralization rates (between 2 and 27%) and microbial biomass C (max. 51 μg C g −1 soil) and no net N immobilization nor mineralization. Application of digestates resulted in high mineral N contents (47–192 mg kg −1 soil) and a decrease of the soil pH. In all three treatments, short-term N 2 O losses after soil application were very small (<0.11 kg N ha −1 after 12 days). Growers can choose the most appropriate treatment option and application moment and location, depending on the local soil and crop requirements and the on-farm facilities. Furthermore, we conclude that the parameters biodegradation potential (based on the biochemical composition) and oxygen uptake rate have potential as less time-consuming proxies for C mineralization to assess the product stability. [ABSTRACT FROM AUTHOR]

Understanding the interactions among organic manure chemical composition, decomposition and nitrogen (N) fertilization is critical for sustainable agriculture management. Six organic manures were incubated in a cultivated black soil with or without N addition for one year, and carbon dioxide (CO 2 ) emissions from these organic manures were monitored. Chemical compositions of the organic manures were determined by elemental analysis, proximate chemical analysis, and carbon (C)-13 nuclear magnetic resonance spectroscopy, and evaluated after cupric-oxide oxidation for lignin biomarkers. During the experimental period, 19–44% of manure C was decomposed without N addition, which decreased to 17–35% with N addition, except for the composted furfural residue with rice dregs. However, during different decomposition stages, N effect changed from stimulation to inhibition, or behaved as increasing inhibition. During stage 1 (days 0–100) when N stimulation effect reached a maximum, CO 2 emissions from manure had positive relationships with labile C fraction indicators, including total sugars, soluble polyphenols, and lignin cinnamyl/vanillyl ratio regardless of N addition. N effect on manure decomposition was related to the C/N ratio and labile organic C content. During stage 2 (days 101–267), N effect shifted to inhibition, with CO 2 emissions from manure negatively related to lignin vanillyl-units content. The magnitude of N inhibition increased linearly with the aromaticity of dissolved organic C, and was strengthened by nitrate in manure. Finally, N inhibition effect reached a maximum during stage 3 (days 268–365), increasing with higher aromatic C in manure. Critical factors for manure decomposition shifted from total sugars, soluble polyphenols, and lignin cinnamyl-units to recalcitrant lignin vanillyl-units and aromatic C fraction, which mediated the type and magnitude of N effect on decomposition. Our results suggested that the potential for enhancing soil C sequestration with organic manures would magnify under combined application with N fertilizer in the long term. [ABSTRACT FROM AUTHOR]

Deep soil stores a large amount of organic carbon (C) and nitrogen (N). However, little is known regarding the interactions between soil C and net N mineralization in deep soil, which complicates the prediction of ecosystem C and N dynamics. In this study, a 150-day laboratory soil incubation experiment was performed under 20 °C and 25 °C to investigate the influence of soil depth and warming on C and net N mineralization and their relationship. Soils were collected from a Hapludalfs profile in a subtropical forest with three depth intervals: 0–10 (topsoil), 10–30 (midsoil), and 30–60 cm (subsoil). Soil microbial community-level physiological profiling (CLPP) was conducted to investigate the role of the microbial community in C and N mineralization. The results demonstrated that both C and net N mineralization rates in subsoil were significantly lower than in topsoil. Compared to topsoil, subsoil had lower temperature sensitivity of C mineralization and relatively higher temperature sensitivity of net N mineralization. Cumulative soil C and net N mineralized were positively correlated in topsoil with the mineralized N per mineralized C showed as 0.19 and 0.31 at 20 °C and 25 °C, respectively. However, there was no significant correlation between cumulative soil C and net N mineralized in subsoil due to the low amount of net N mineralization. The lack of labile C source and degradable organic N were believed to limit the net N mineralization in subsoil. The microbial community in topsoil used relatively more easily decomposable carbohydrates and carboxylic acids, which favored C mineralization. In contrast, the microbial community in subsoil had relatively high utilization of amino acids (N-containing substrates), which indicated there was N limitation. This distinguished substrate utilization patterns of microbial communities could explain the observed C and N mineralization rates among the soil depths, and suggests that the microbial community played an important role in soil C and N mineralization. The decoupled relationships between soil C and net N mineralization in deep soil and their differentiated responses to warmer temperatures among soil depths indicated that deep soil should be considered separately from topsoil for ecosystem C and N cycling, especially for ecosystem C dynamic models. [ABSTRACT FROM AUTHOR]

As pastagens geralmente perdem seu potencial produtivo e vigor de rebrota nos primeiros anos, frequentemente associada à falta de adubação nitrogenada. O objetivo deste foi verificar o efeito de fontes e doses de adubação nitrogenada na atividade microbiana (carbono da biomassa microbiana e carbono do CO2 liberado) e na fertilidade do solo cultivado com Brachiaria brizantha cv. Xaraés. O delineamento experimental foi em blocos casualizados, em arranjo fatorial 3 x 4, envolvendo três fontes de nitrogênio (uréia, sulfato de amônio e Ajifer-L40) e quatro doses de nitrogênio (0, 100, 200 e 400 kg ha-1), nas profundidades 0 - 0,10 e 0,10 - 0,20 m, com trêsrepetições. O aumento nas doses de nitrogênio, na camada 0,0 a 0,10 m de profundidade, reduziu os valores de pH, MO, K+, Ca2+, Mg2+, SB e V%. O Ajifer e a uréia elevaram os valores de Ca2+ na camada 0,10 - 0,20 m, e as doses de 100 e 200 kg ha-1 aumentaram os valores de Mg2+ e SB. Em doses elevadas o sulfato de amônio acidificou o solo. A perda de carbono pela elevada atividade microbiana pode estar relacionado ao estresse metabólico devido à acidificação do solo.A aplicação de 100 kg ha-1 de nitrogênio acarretou as menores perdas de carbono pela atividade microbiana.Pastures usually lose their yield potential and re-growth energy in a few years, most often due to the lack of nitrogen fertilization. Theobjective of this study was to verify the effect of sources and levels of nitrogen (N) fertilization, under microbial activity (carbon of microbial biomass and carbon released as CO2) and fertilityof soil cropped with Brachiaria brizantha cv. Xaraés. The experimental design was randomized, organized under a 3 x 4 factorial scheme, with three nitrogen sources (urea, ammonium sulfate and Ajifer-L40) and four nitrogen levels (0, 100, 200 and 400 kg ha-1), analyzed on two depths (0 - 0,10 e 0,10-0,20 m), with 3 replications. The higher levels of N doses, the 0 - 0.10 m depths, reduced the values of pH, MO, K+, Ca2+, Mg2+, SB and V%. Ajifer and urea resulted in higher values of Ca2+, in the depths of 0.10 – 0.20 m, and the values of Mg2+ and SB exhibited high values with the doses of 100 and 200 kg ha-1 levels of N. The higher levels of ammonium sulfate resulted in soil acidification. Soil carbon loss, due to the high microbial activity, could be the result of metabolic stress caused by soil acidification. The application of 100 kg ha-1 of nitrogen was the best fertilizing level, considering the smaller loss of soil carbon by microbial activity.

Despite our current understanding of soil C and N interactions, less is known about the response and feedback of C mineralization to soil P availability driven by microorganisms. To better understand these interactions, soils with long-term P-sufficient NPK fertilization (available P: 13.4 mg kg −1 ) and P-deficient NK fertilization (available P: 0.96 mg kg −1 ) were incubated with and without glucose. CO 2 emissions were monitored to characterize C mineralization during the incubation. The soil bacterial community structure, quantity and metabolic activity were evaluated using high-throughput sequencing, qPCR and microcalorimetric dynamics. Compared with P-sufficient soils, P-deficient soils had significantly lower basal respiration, but a significantly higher net mineralization of added glucose, probably due to higher energy cost of soil microorganisms. Glucose addition promoted microbial biomass and activity, particularly in P-deficient soils, and this improvement was maintained for at least 70 days. Shifts in bacterial community composition were induced by a predominance of several specific taxonomic groups, all of which were capable of solubilizing P in soils. P-deficiency decreases the retention of exogenous labile C into soil. Adding labile C to P-deficient soils may shift P from relatively unavailable soil-bound pools into microbial biomass pools through pool cycling. Our results indicated negative effects of P-deficiency on soil C retention, as well as positive effects of labile C on soil P availability in arable soils. [ABSTRACT FROM AUTHOR]