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Nitrogen (N) released from soil organic matter (SOM) is quantitatively important for crop uptake, even when adequate fertiliser N is supplied. Understanding of SOM has shifted to recognise distinct fractions that correlate with properties such as turnover time, carbon (C) and N content, and chemical composition. Yet, how these fractions relate to N supply from SOM is poorly understood. This study aimed to link N mobilisation and C stability in coarse (≥50 μm) and fine (≤50 μm) fractions, and evaluate the roles of these fractions in supplying N in cropping soil. Soils from long‐term continuous cotton, cotton‐vetch, and cotton‐wheat rotations and a nearby uncleared site (NV) were separated into coarse and fine fractions, left as whole soil, or dispersed and freeze‐dried as a fractionation control. Initial C chemistry in fractions and whole soils was measured by solid state 13C NMR spectroscopy. N mobilisation and CO2 loss were measured over a 14‐day incubation experiment. In the cropping soils, net immobilisation of N was measured in the separate fractions, while net mobilisation was found in the whole soils. In the NV soil, N mobilisation was greater in the fine fraction. C mineralisation followed the order fine fraction > fractionation control = coarse fraction > whole soil. C stability was best explained by physical protection within whole soil structure rather than chemical recalcitrance or mineral stabilisation. The results revealed an unexpected contrast between C and N mineralisation from SOM fractions and demonstrated the importance of soil aggregates for SOM stability. We show a cautionary impact of fractionation on C and N dynamic, highlighting the need for further research to understand the synergistic behaviour of SOM fractions in whole soils. [ABSTRACT FROM AUTHOR]

Bacteria and fungi are core microorganisms in diverse ecosystems, and their cross‐kingdom interactions are considered key determinants of microbiome structure and ecosystem functioning. However, how bacterial‐fungal interactions mediate soil organic carbon (SOC) dynamics remains largely unexplored in the context of artificial forest ecosystems.Here, we characterised soil bacterial and fungal communities in four successive planting of Eucalyptus and compared them to a neighbouring evergreen broadleaf forest. Carbon (C) mineralisation combined with five C‐degrading enzymatic activities was investigated to determine the effects of successive planting of Eucalyptus on SOC dynamics.Our results indicated that successive planting of Eucalyptus significantly altered the diversity and structure of soil bacterial and fungal communities and increased the negative bacterial‐fungal associations. The bacterial diversity significantly decreased in all Eucalyptus plantations compared to the evergreen forest, while the fungal diversity showed the opposite trend. The ratio of negative bacterial‐fungal associations increased with successive planting of Eucalyptus due to the decrease in SOC, ammonia nitrogen (NH4+‐N), nitrate nitrogen (NO3−‐N) and available phosphorus (AP). Structural equation modelling indicated that the potential cross‐kingdom competition, based on the ratio of negative bacterial‐fungal correlations, was significantly negatively associated with the diversity of total bacteria and keystone bacteria, thereby increasing C‐degrading enzymatic activities and C mineralisation.Synthesis and applications: Our results highlight the regulatory role of the negative bacterial‐fungal association in enhancing the correlation between bacterial diversity and C mineralisation. This suggests that promoting short‐term successive planting in the management of Eucalyptus plantations can mitigate the impact of this association on SOC decomposition. Taken together, our study advances the understanding of bacterial‐fungal negative associations to mediate carbon mineralisation in Eucalyptus plantations, giving us a new insight into SOC cycling dynamics in artificial forests. [ABSTRACT FROM AUTHOR]

Purpose: Digestates from anaerobic digestion are increasingly used in agriculture. There is thus a need for better understanding of digestates' value as organic soil amendments, and how this varies depending on the process parameters and post-treatments applied. Methods: A range of fifteen digestates (raw, solid, phase separated, and composted digestates), originating from farm and centralised anaerobic digestion sites were characterised. Carbon mineralisation and soil aggregate stability (AS) dynamics following the addition of the digestates to soil were monitored over a 182-day incubation period at 20 °C. Results: The mineralisation of carbon varied significantly between digestates, with the lowest percentage of carbon lost at 11.45% for composted digestate, and the highest at 49.27% for a solid batch digestate. Using hierarchical clustering of soil AS analysis at several sample dates, digestates were classified into four groups: those inducing (1) rapid but transient improvement of AS, (2) slower, temporary improvement of AS, (3) immediate improvement followed by a longer-lasting increase in AS, (4) minor or non-significant improvement in AS. Conclusion: Phase separation and composting of digestates were found to have more impact than other process parameters in determining the rate of mineralisation and dynamics in AS. Impact: Characterising and classifying digestates by their potential impact on soil structure would help to improve decision making for digestate production and sustainable use in agriculture. [ABSTRACT FROM AUTHOR]

• Carbon mineralization in mafic and ultramafic formations offers an attractive CO2 storage option. • Several key technical factors affecting the success, scale, and cost of in-situ carbon mineralization projects are discussed. • Overview of pilot tests, projects, and associated costs is provided. Carbon mineralisation in underground mafic and ultramafic formations, known as in-situ carbon mineralisation, has emerged as an attractive technology for permanent CO 2 storage. Despite its potential, this method has received limited attention compared to conventional CO 2 storage in sedimentary formations. However, increasing interest from countries and companies in utilising this approach to permanently store CO 2 via carbon mineralisation has grown in recent years as part of the wider carbon capture and storage expansion seen globally. This review paper aims to provide an in-depth overview of in-situ carbon mineralisation technology. The paper covers key factors crucial for successful implementation, including water consumption, CO 2 injection rate, risk of CO 2 leakage, injectivity, fracture characterisation, pressure management and induced seismicity, thermal effects, surface area of minerals, groundwater contamination, injection strategy, monitoring of confinement, and reservoir modelling. The paper also discusses pilot tests and projects, highlighting their outcomes. Furthermore, it discusses the costs associated with in-situ carbon mineralisation and provides a case study. The primary objective of this paper is to increase awareness and understanding of this relatively new technology within the carbon capture and storage industry. By shedding light on the benefits and challenges of carbon mineralisation in mafic and ultramafic formations, this review aims to encourage further research, development, and adoption of this promising approach for CO 2 emissions reduction and permanent CO 2 storage. [ABSTRACT FROM AUTHOR]

A variety of organic feedstocks can be used for anaerobic digestion, resulting in digestates with different compositions, affecting the fertiliser value. Therefore, two experiments were conducted to assess (1) differences in the nitrogen (N) fertiliser value of seven digestates from different feedstocks in a 2-year field experiment with spring wheat, and (2) the degradability of organic matter (OM) in the digestates within an aerobic incubation experiment. In the field, mineral fertiliser equivalents were in a range of 18–60% (1st year) and 39–83% (2nd year). Fertiliser properties could describe 58.9–74.2% of the N offtake variance among digestates. In the incubation experiment, digestates produced 720–1900 mg CO2-C kg−1. After 56 days, 61% of organic C added by food waste digestate has been mineralised, compared to 16–22% for the other digestates. Digestate composition (C/N, Corg/Norg, carbonate, cellulose, lignin, and crude fibre) could explain 90.4% of the CO2 evolution. In both experiments, digested food waste stood out among digestates with the highest N offtake and highest OM mineralisation. In conclusion, differences in fertiliser value and OM degradability could be related to compositional variations. However, apart from food waste, the composition had only minor influence on digestate performance after soil application. [ABSTRACT FROM AUTHOR]

Permanent CO 2 storage in basalts through mineralisation offers a promising solution for reducing carbon emissions and mitigating climate change. This study focuses on the impact of potential mineralisation on the flow properties of the basaltic material. Fluid flow evolution before and after exposure to CO 2 dissolved in seawater is measured in terms of hydraulic conductivity and permeability under field-like conditions over 1 to 3.5 months. Permeability reduction of up to one order of magnitude suggests that porosity decreases due to mineral precipitation after CO 2 exposure. X-ray tomography measurements of the tested cores reveal a maximum porosity decrease of 1.5% at the given resolution (50 μ m /px). To better understand eventual modifications of the connected pore network after mineralisation, fluid flow simulations are performed on the 3D pore network of the material that is reconstructed directly from the acquired x-ray images. A double porosity is proposed: macro-porosity as visible from the tomographies (pores > 50 μ m) and micro-porosity (pores < 50 μ m). To reproduce the post-CO 2 exposure flow, reduction of macro-porosity is not enough. Instead, a decrease of the micro-pores is necessary by up to 43%. The experimental and numerical results suggest that potential mineralisation can substantially modify the pore space of the intact basaltic material and consequently impact storage efficiency if flow is not preserved. • The impact of CO 2 -rich seawater exposure on the flow properties of basalts is studied. • Reduced flow by up to one order of magnitude is measured after 2 months CO 2 exposure. • A double-scale porosity is considered to simulate the material's pore network. • Pore network modelling revealed mineralisation is likely to occur in the micropores. [ABSTRACT FROM AUTHOR]

Arbuscular mycorrhizal fungi are a fundamental contributor to soil carbon mineralisation and nutrient cycling in saline soils. This study aimed to evaluate the interactions between arbuscular mycorrhizal fungi (Glomus mosseae) (G), tea residue (T), macroalgae biomass (M) and its subsequent effects on carbon mineralisation, actinomycetes counts, nutrients content, chlorophyll content, and corn growth (Zea mays L.). T wenty four pots with eight treatments, control (C), macroalgae (M), tea residue (T), Glomus mosseae (G), Glomus mosseae + macroalgae (G+M), Glomus mosseae + tea residue (G+T), macroalgae+ tea residue (M+T) and Glomus mosseae + tea residue+ macroalgae (G+T+M) were randomly distributed in the field using randomised complete design (RCD). Results showed that only treatment T had the highest value of carbon mineralisation (0.216 mg C g-1 soil day), while it was lower (0.177 mg C g-1 soil day) in the G+T treatments. Additionally, the highest values of actinomycetes, chlorophyll, phosphorous content and roots weight were 4.2 10-6 CFU g-1, 35 SPAD, 0.4 % and 55 g, respectively in G+T treatments. In contrast, the addition of T, M and G alone did not increase phosphorous content as compared to the control. In conclusion, the combination of tea residue and macroalgae biomass with Glomous mossea affected carbon decomposition and increased the number of actinomycetesas as well as nutrients content. This can be beneficial to ecosystems through facilitating carbon conservation and microbial diversity in arid saline soils.. [ABSTRACT FROM AUTHOR]

Plant roots are generally considered to decompose slower than shoots and contribute more to accumulation of soil organic matter, and management history is expected to shape the structure and function of decomposer communities in soil. Here we study the effect of chemical characteristics of shoots and roots from fodder radish (Raphanus sativus oleiformis L.), a widely used cover crop, on the release of their C and N after addition to soil. Shoots and roots were incubated for 180 d at 20°C using four soils with different management histories (organic versus mineral fertiliser, with and without use of cover crops), and the release of CO2 and extractable mineral N was determined. More shoot C than root C was mineralised during the first 10 d of incubation. After 180 d, 58% of the C input was mineralised with no difference between shoots and roots. At the end of incubation, shoots had released more N (42% of shoot N) than roots (28% of root N). Moreover, management history did not affect net mineralisation of added plant C. Residues incubated in soil with a management history involving cover crops showed an enhanced net N mineralisation. Therefore, long-term decomposition of C added in radish shoots and roots is unaffected by differences in chemical characteristics or soil management history. However, the net mineralisation of N in shoots is faster than for N in roots, and net N mineralisation of added materials is higher in soil with than without a history of cover crops. Abbreviations: CC: cover crop; IF: inorganic fertilizer; M: manure

Plant roots are generally considered to decompose slower than shoots and contribute more to accumulation of soil organic matter, and management history is expected to shape the structure and function of decomposer communities in soil. Here we study the effect of chemical characteristics of shoots and roots from fodder radish (Raphanus sativus oleiformis L.), a widely used cover crop, on the release of their C and N after addition to soil. Shoots and roots were incubated for 180 d at 20°C using four soils with different management histories (organic versus mineral fertiliser, with and without use of cover crops), and the release of CO2 and extractable mineral N was determined. More shoot C than root C was mineralised during the first 10 d of incubation. After 180 d, 58% of the C input was mineralised with no difference between shoots and roots. At the end of incubation, shoots had released more N (42% of shoot N) than roots (28% of root N). Moreover, management history did not affect net mineralisation of added plant C. Residues incubated in soil with a management history involving cover crops showed an enhanced net N mineralisation. Therefore, long-term decomposition of C added in radish shoots and roots is unaffected by differences in chemical characteristics or soil management history. However, the net mineralisation of N in shoots is faster than for N in roots, and net N mineralisation of added materials is higher in soil with than without a history of cover crops. [ABSTRACT FROM AUTHOR]

Recent publications on the successful mineralisation of carbon dioxide in basalts in Iceland and Washington State, USA, have shown that mineral storage can be a serious alternative to more mainstream geologic carbon storage efforts to lock away permanently carbon dioxide. In this study we look at the pore solution chemistry and mineralogy of basaltic glass and crystalline basalt under post-injection conditions, i.e. after rise of the pH via matrix dissolution and the first phase of carbonate formation. Experimental findings indicate that further precipitation of carbonates under more alkaline conditions is highly dependent on the availability of divalent cations. If the pore water is deficient in divalent cations, smectites and/or zeolites will dominate the secondary mineralogy of the pore space, depending on the basalt matrix. At low carbonate alkalinity no additional secondary carbonates are expected to form meaning the remaining pore space is lost to secondary silicates, irrespective of the basalt matrix. At high carbonate alkalinity, some of this limited storage volume may additionally be occupied by dawsonite −if the Na concentration in the percolating groundwater (brine) is high. Using synthetic seawater as a proxy for the groundwater composition and thus furnishing considerable amounts of divalent cations to the carbonated solution, results in massive precipitation of calcite, magnesite, and other Ca/Mg-carbonates under already moderate carbonate alkalinity. More efficient use of the basaltic storage volume can thus be attained by promoting formation of secondary carbonates compared to the inevitable formation of secondary silicate phases at higher pH. This can be done by ensuring that the pore water does not become depleted in divalent cations, even after carbonate formation. Using seawater as carbonating fluid or injection of CO 2 into the basaltic oceanic crust, where saline fluids percolate, can reach this goal. However, such an approach needs sophisticated reactive transport modelling to adjust CO 2 injection rates in order to avoid too rapid carbonate deposition and clogging of the pore space too close to the injection well. [ABSTRACT FROM AUTHOR]

An understanding of the heterotrophic respiration part of belowground processes, as affected by active carbon, is crucial in order to predict the response of carbon emission from soil organic carbon, in forest ecosystems and climatic changes. However, in the current literature, most soil respiration measurements are interpreted without simultaneous information on active carbon pool dynamics. In this study, path analysis was used to demonstrate the impacts of microbial biomass carbon, water-soluble organic carbon and mineralisation carbon on soil heterotrophic respiration. It was found that variations in heterotrophic respiration were well related to mineralisation carbon and microbial biomass carbon, whereas water-soluble organic carbon was generally not adequate indicators of carbon effluxes. Mineralisation carbon and microbial biomass carbon have significant correlation relationships and indirect effects with each other on heterotrophic respiration, indicating a possible stimulatory effect of labile carbon and microbial activity on microbial processing of carbon. A single parameter recommended to quantify soil heterotrophic respiration in southern China is mineralisation carbon, as the most efficient measurement of soil variable. [ABSTRACT FROM AUTHOR]

Carbon mineralisation has the potential to sequester and safely store large amounts of carbon dioxide (CO 2 ). However, this technology has not seen the same level of development as geological storage in sedimentary reservoirs. This is primarily because early work on carbonation of minerals focused on high temperature and pressure process routes, which are cost-prohibitive to accelerate the reaction from geological to industrial time scales. Bacteria-mediated carbon mineralisation of mine tailings [1] overcomes this impediment because it occurs at ambient temperature and standard pressure and the rock is already crushed. With abundant mafic and ultramafic rock, a highly developed mining sector, and a warm climate that promotes fast carbonation reactions, Australia presents an optimal region to develop this technology. We assess the mineralisation potential of Australia's existing and future nickel mine tailings and estimate that this carbon sink could sequester up to 2,171 Megatons (Mt) of CO 2 . [ABSTRACT FROM AUTHOR]

Monsoon-induced coastal upwelling, land run-off, benthic and atmospheric inputs make the western Indian shelf waters biologically productive that is expected to lead to high rates of mineralisation of organic matter (OM) in the sediments. Dissimilatory sulphate reduction (SR) is a major pathway of OM mineralisation in near-shore marine sediments owing to depletion of other energetically more profitable electron acceptors (O, NO , Mn and Fe oxides) within few millimetres of the sediment-water interface. We carried out first ever study to quantify SR rates in the inner shelf sediments off Goa (central west coast of India) using the S radiotracer technique. The highest rates were recorded in the upper 10 cm of the sediment cores and decreased gradually thereafter below detection. Despite significant SR activity in the upper ∼12 to 21 cm at most of the sites, pore water sulphate concentrations generally did not show much variation with depth. The depth integrated SR rate (0.066-0.46 mol m year) decreased with increasing water depth. Free sulphide was present in low concentrations (0-3 μM) in pore waters at shallow stations (depth <30 m). However, high build-up of sulphide (100-600 μM) in pore waters was observed at two deeper stations (depths 39 and 48 m), 7-11 cm below the sediment-water interface. The total iron content of the sediment decreased from ∼7 to 5 % from the shallowest to the deepest station. The high pyrite content indicates that the shelf sediments act as a sink for sulphide accounting for the low free sulphide levels in pore water. In the moderately organic rich (2-3.5 %) sediments off Goa, the measured SR rates are much lower than those reported from other upwelling areas, especially off Namibia and Peru. The amount of organic carbon remineralised via sulphate reduction was ∼0.52 mol m year. With an estimated average organic carbon accumulation rate of ∼5.6 (±0.5) mol m year, it appears that the bulk of organic matter gets preserved in sediments in the study region. [ABSTRACT FROM AUTHOR]

Subsoils play an important role within the global C cycle, since they have high soil organic carbon (SOC) storage capacity due to generally low SOC concentrations. However, measures for enhancing SOC storage commonly focus on topsoils. This study assessed the long-term storage and stability of SOC in topsoils buried in arable subsoils by deep ploughing, a globally applied method for breaking up hard pans and improving soil structure to optimize crop growing conditions. One effect of deep ploughing is translocation of SOC formed near the surface into the subsoil, with concomitant mixing of SOC-poor subsoil material into the 'new' topsoil. Deep-ploughed croplands represent unique long-term in situ incubations of SOC-rich material in subsoils. In this study, we sampled five loamy and five sandy soils that were ploughed to 55-90 cm depth 35-50 years ago. Adjacent, similarly managed but conventionally ploughed subplots were sampled as reference. The deep-ploughed soils contained on average 42 ± 13% more SOC than the reference subplots. On average, 45 years after deep ploughing, the 'new' topsoil still contained 15% less SOC than the reference topsoil, indicating long-term SOC accumulation potential in the topsoil. In vitro incubation experiments on the buried sandy soils revealed 63 ± 6% lower potential SOC mineralisation rates and also 67 ± 2% lower SOC mineralisation per unit SOC in the buried topsoils than in the reference topsoils. Wider C/N ratio in the buried sandy topsoils than in the reference topsoils indicates that deep ploughing preserved SOC. The SOC mineralisation per unit SOC in the buried loamy topsoils was not significantly different from that in the reference topsoils. However, 56 ± 4% of the initial SOC was preserved in the buried topsoils. It can be concluded that deep ploughing contributes to SOC sequestration by enlarging the storage space for SOC-rich material. [ABSTRACT FROM AUTHOR]

The cycling of soil organic matter (SOM) and carbon (C) within the soil is governed by the presence of key macronutrients, particularly nitrogen (N) and phosphorus (P). The relative ratio of these nutrients has a direct effect on the potential rates of microbial growth and nutrient processing in soil and thus is fundamental to ecosystem functioning. However, the effect of changing soil nutrient stoichiometry on the small organic molecule (i.e., metabolite) composition and cycling by the microbial community remains poorly understood. Here, we aimed to disentangle the effect of stoichiometrically balanced nutrient addition on the soil metabolomic profile and apparent microbial carbon use efficiency (CUE) by adding a labile C source (glucose) in combination with N and/or P. After incorporation of the added glucose into the microbial biomass (48 h), metabolite profiling was undertaken by ultra-performance liquid chromatography-tandem mass spectrometry (UPLC-MS/MS). 494 metabolites were identified across all treatments mainly consisting of lipids (n = 199), amino acids (n = 118) and carbohydrates (n = 43), >97% of which showed significant changes in concentration between at least one treatment. Overall, glucose-C addition generally increased the synthesis of other carbohydrates in soil, while addition of C and N together increased peptide synthesis, indicative of protein formation and turnover. The combination of C and P significantly increased the number of fatty acids synthesised. There was no significant change in the PLFA-derived microbial community structure or microbial biomass following C, N and P addition. Further, N addition led to an increase in glucose-C partitioning into anabolic processes (i.e., increased CUE), suggesting the microbial community was N, but not P limited. Based on the metabolomic profiles observed here, we conclude that inorganic nutrient enrichment causes substantial shifts in both primary and secondary metabolism within the microbial community, leading to changes in resource flow and thus soil functioning, however, the microbial community illustrated significant metabolic flexibility. • Metabolomics reveal fundamental metabolite synthesis with changing stoichiometry. • C + N addition increased carbohydrates and peptides and increased substrate usage. • N limitation had the greatest impact on the soil's metabolic profile. • C + P addition significantly increased fatty acid synthesis and accumulation. [ABSTRACT FROM AUTHOR]

The net annual exchange of carbon between the atmosphere and terrestrial ecosystems is of prime importance in determining the concentration of CO2 ([CO2]) in the atmosphere and consequently future climate. Carbon loss occurs primarily through soil respiration; it is known that respiration is sensitive to the global changes in [CO2] and temperature, suggesting that the net carbon balance may change in the future. However, field manipulations of temperature and [CO2] alter many important environmental factors so it is unclear how much of the observed alterations in soil respiration is due to changes of microbial function itself instead of changes to the physical and chemical environment. Here we focus on resolving the importance of changes in the microbial community in response to warming and elevated [CO2] on carbon mineralisation, something not possible in field measurements. We took plant material and soil inocula from a long running experiment where native grassland had been exposed to both warming and elevated CO2 and constructed a reciprocal transplant experiment. We found that the rate of decomposition (heterotrophic respiration) was strongly determined by the origin of the microbial community. The combined warming + elevated CO2 treatment produced a soil community that gave respiration rates 30% higher when provided with shoot litter and 70% for root litter than elevated CO2 treatment alone, with the treatment source of the litter being unimportant. Warming, especially in the presence of elevated CO2, increased the size of the apparent labile carbon pool when either C3 or C4 litter was added. Thus, the metabolic activity of the soil community was affected by the combination of warming and elevated CO2 such that it had an increased ability to mineralise added organic matter, regardless of its source. Therefore, soil C efflux may be substantially increased in a warmer, high CO2 world. Current ecosystem models mostly drive heterotrophic respiration from plant litter quality, soil moisture and temperature but our findings suggest equal attention will need to be paid to capturing microbial processes if we are to accurately project the future C balance of terrestrial ecosystems and quantify the feedback effect on atmospheric concentrations of CO2. [ABSTRACT FROM AUTHOR]

Recent studies have shown both increased (positive priming) and decreased (negative priming) mineralisation of native soil organic carbon (SOC) with biochar addition. However, there is only limited understanding of biochar priming effects and its C mineralisation in contrasting soils at different temperatures, particularly over a longer period. To address this knowledge gap, two wood biochars (450 and 550 °C; d13C -36.4%) were incubated in four soils (Inceptisol, Entisol, Oxisol and Vertisol; d13C -17.3 to -28.2%) at 20, 40 and 60 °C in the laboratory. The proportions of biochar- and soil-derived CO2-C were quantified using a two-pool C-isotopic model. Both biochars caused mainly positive priming of native SOC (up to +47 mg CO2-C g-1 SOC) in the Inceptisol and negative priming (up to -22 mg CO2-C g-1 SOC) in the other soils, which increased with increasing temperature from 20 to 40 °C. In general, positive or no priming occurred during the first few months, which remained positive in the Inceptisol, but shifted to negative priming with time in the other soils. The 550 °C biochar (cf. 450 °C) caused smaller positive priming in the Inceptisol or greater negative priming in the Entisol, Oxisol and Vertisol at 20 and 40 °C. At 60 °C, biochar caused positive priming of native SOC only in the first 6 months in the Inceptisol. Whereas, in the other soils, the native SOC mineralisation was increased (Entisol and Oxisol) and decreased (Vertisol) only after 6 months, relative to the control. At 20 °C, the mean residence time (MRT) of 450 °C and 550 °C biochars in the four soils ranged from 341 to 454 and 732-1061 years, respectively. At 40 and 60 °C, the MRT of both 450 °C biochar (25-134 years) and 550 °C biochar (93-451 years) decreased substantially across the four soils. Our results show that biochar causes positive priming in the clay-poor soil (Inceptisol) and negative priming in the clay-rich soils, particularly with biochar ageing at a higher incubation temperature (e.g. 40 °C) and for a high-temperature (550 °C) biochar. Furthermore, the 550 °C wood biochar has been shown to persist in soil over a century or more even at elevated temperatures (40 or 60 °C). [ABSTRACT FROM AUTHOR]

Highlights: [•] The first study to report temperature sensitivity of biochar in contrasting soils. [•] Soil type influenced the temperature sensitivity (Q10) of biochar mineralisation. [•] Q10 of biochar-C was similar or lower than native soil organic C (SOC). [•] The presence of biochar decreased Q10 of native SOC in some soils at 20–40°C range. [•] Q10 of biochar-C in soil decreased with increasing incubation temperature. [ABSTRACT FROM AUTHOR]

The availability of soil nutrients, which are recycled through the decomposition of crop residues, is important for the management of cropped soils. However, knowledge regarding the influence of contact between crop residues and soil on the dynamics of carbon (C) and nitrogen (N) in soil is limited. In particular, the effect of particle size on decomposition is not well-known, and conceptual approaches for modelling the soil-residue contact in a decomposition model remain scarce. Therefore, we analysed and modelled the effect of maize stem particle length on decomposition. We incubated maize stem residues with particle sizes of 0.02, 0.5, 2 and 5 cm in length in a loamy soil at 25 °C over 301 days. We continuously measured the mineralisation of C and N and determined the chemical evolution of the remaining particles. We used the decomposition model CANTIS which takes into account the soil-residue contact, using a contact factor, K. The decomposition rates of smaller maize particles were higher than those of larger particles during the early phases of decomposition. However, these differences were not maintained after 301 days. These results suggest that a larger size of the maize particles only slowed the rate of mineralisation in the short term but did not modify decomposition in the medium term. We proposed a new formalism for expressing the changes in soil-residue contact with different particle sizes. The contact factor K was calculated using the standardised specific surface area and can be applied more widely to residues that differ in morphology and density. [ABSTRACT FROM AUTHOR]

ABSTRACT To determine the relationship between soil organic matter (SOM) decomposition and chemistry in the permafrost region of the Qinghai-Tibet Plateau (QTP), 300-day laboratory incubations at 25°C and chemical fractionation were performed to characterise the mineralisation dynamics of organic carbon from soils under five vegetation conditions. The respiration rates in wet meadows were the highest, followed by the Kobresia pygmaea meadow and K. robusta meadow. After the incubation period, all four fractions of SOM - non-polarity soluble, water soluble, holocellulose and lignin contents - showed some decline, and the SOM decreased by 16-20 per cent in soils of the steppe, meadow and wet meadow. These results suggest that a large proportion of the organic matter in soils of the permafrost region in the QTP is mineralisable. Based on the changes in chemical fractions of organic matter, it could be determined that soils with higher water-soluble fractions had higher rates of carbon mineralisation, while the mechanisms involved in the respiration of different chemical fractions are complicated. Copyright © 2013 John Wiley & Sons, Ltd. [ABSTRACT FROM AUTHOR]

The exothermic carbonation reaction includes the degradation of alkaline earth metal (mainly Mg-, Ca-) oxides, hydroxides or silicates under participation of carbon dioxide under aqueous conditions and the formation of stable carbonates with long-term storage of carbon dioxide. The extent of reaction depends on different influencing factors, which significantly affect the economic and ecological feasibility of this technology. With special regard to the possibilities of upscaling and balancing in the context of life cycle analyses for the carbon capture and usage approach, various material-specific and process-related parameters and also combinations of these have been tested experimentally and evaluated. Hereby, significant differences in the carbonation extent were identified with achieved carbonation degrees from below 5 up to 60%, corresponding to 305 kg CO2 /t feed. This study is a comprehensive investigation of those material-specific and process-related parameters and their combination and aims to ensure the economic viability of enhanced weathering by increasing the degree of carbonation. [Display omitted] • Optimised process parameters enhance the carbonation reaction. • CO 2 uptake increased by 83.7%, corresponding to 305 kg CO2 /t olivine. • Carbonation with scalable process parameters for industrial usage possible. [ABSTRACT FROM AUTHOR]

Abstract: This work is concerned with the effect of five earthworm species on short-term soil dynamics through carbon (C) mineralisation and large soil aggregate characteristics (production, stability, organic matter content and composition) in laboratory experiments. We hypothesised that the influence of earthworms on soil behaviour depends on individual species and land use history. Substrates were a sequence of three similar luvisols that had been subjected to different land use histories and represented increasing C contents from 10 mg kg−1 (cropped soil), to 20 mg kg−1 (5-year-old pasture soil) and 33 mg kg−1 (permanent pasture soil). We found that relative C mineralisation was slower in pasture than in cropped soils, which can be explained by differences in the physical protection of soil organic matter (SOM). Land use history influenced (i) the amount of large macro-aggregate production through earthworm behaviour (casting activity), and (ii) the size distribution of water stable soil fractions within the large macro-aggregate produced. No effect of earthworm species on SOM composition was observed with near infrared spectrometry indicating that the chemistry of large macro-aggregates was mainly driven by land use type. Earthworm species had more pronounced effects on physical (large aggregate production and stability) than on biological (C mineralisation promotion) or biochemical (SOM composition) features. This paper shows that, although earthworm effects on soil processes are now obvious, a number of factors may interact in such complex systems so that we should hesitate to make generalisations. [Copyright &y& Elsevier]

Abstract: Soil organic matter (SOM) content and texture are important factors affecting carbon (C) and nitrogen (N) mineralisation under constant soil moisture but their effects on organic matter mineralisation and associated biogenic gas (carbon dioxide (CO2) and nitrous oxide (N2O)) production during dry/wet cycles is poorly understood. A laboratory incubation study was conducted to quantify CO2 and N2O production during sequential dry/wet cycles and under constant soil moisture conditions along a gradient of SOM contents in two soil types representing different texture classes (silt loam vs. clay loam). Three soil moisture treatments were established: wet (WW; field capacity), moderately dry (MD; 120% of soil moisture content (SMC) at wilting point (WP)) and very dry (VD; 80% of SMC at WP). To each of the two ‘dry’ treatments two different dry/wet treatments were applied where the soils were either maintained continuously dry (MD & VD) or subjected to three sequential 20-day long dry/wet cycles (MDW & VDW) during the treatment phase of the experiment. At field capacity soil moisture content, the rate of C mineralisation increased with increases in SOC content and the increase per unit of C was twice as high in silt loam (0.30mgCO2-Cg−1 SOCd−1) as in clay loam (0.13mgCO2-Cg−1 SOCd−1) soils. N2O-N emissions also increased with increasing in SOC content. However, in contrast to C mineralisation, the effect was four-fold greater for clay loam (1.38μgN2O-Ng−1 SOCd−1) than silt loam (0.32μgN2O-Ng−1 SOCd−1) soils. Following rewetting, the VDW and MDW soils produced a short-term C mineralisation flush that was, on average, 30% and 15% greater, respectively, than in WW soils. However, the flush of C mineralisation was not sufficient to compensate for the reduction in mineralisation during the drying phase of each cycle, resulting in a lower total C mineralisation from MDW and VDW soils, on average, compared with WW soils over the three sequential dry/wet cycles. The C mineralisation flush also remained a relatively constant proportion of the total C mineralised from both silt loam (23%) and clay loam soils (22%), irrespective of their SOC content. In contrast, the short-term flush of N2O that followed rewetting of dry soil accounted for 62% and 68% of the total N2O emissions from silt loam and clay loam soils, respectively. On average, the total N2O emissions from dry/wet treatments imposed on silt loam and clay loam soils were 33% and 270% greater, respectively, than from the WW treatments, though the effect varied greatly and depended on SOC content. Overall, N2O emissions were highest where we had a combination of fine texture, an adequate supply of available C (i.e. high SOM content), and a water-filled pore space (WFPS) > 0.60 cm cm−3 at field capacity. Prediction of C mineralisation over dry/wet cycles using mineralisation data from soils at constant moisture content is possible, but knowledge of the stress history for the soil would be required to improve accuracy. The prediction of N2O-N emissions during dry/wet cycles using emission data from soils at constant moisture was very inaccurate, due to the inherent spatial variability of N2O emissions. [Copyright &y& Elsevier]

Abstract: To formulate best management practices for animal slurry, it is important to understand and predict its decomposition in the soil. Slurry decomposition dynamics can be studied by measuring CO2 fluxes and soil mineral nitrogen concentration during laboratory incubations and subsequently calibrating a simulation model. Carbon and nitrogen dynamics are linked and both should be properly simulated. In this work we wanted to identify the tradeoffs between errors in the simulation of C respiration and of soil inorganic N concentration. We optimised six parameters of CN-SIM (a mechanistic dynamic simulation model), using data of respired C and soil inorganic N measured during a 180-day laboratory incubation of five dairy slurries on three soils. Optimisation was carried out with a multi-objective genetic algorithm (NSGA-II), by minimising the Relative Root Mean Squared Error (RRMSE) between observations and simulations. The simulation of C respiration was frequently conflicting with the simulation of inorganic N, i.e. low RRMSE–CO2 corresponded with high RRMSE–N and vice versa. When minimising RRMSE–CO2 a set of parameters was obtained that enhanced microbial N immobilisation and reduced the turnover of the organic pools, to match the observed decrease of inorganic N in the 28 days after slurry addition to soil. Remineralisation occurring in the following 150 days caused a marked overestimation of inorganic N. When minimising RRMSE–N, the optimisation provided parameters that strongly reduced remineralisation of immobilised N by markedly diminishing C respiration, with a consequent underestimation of CO2 emission. A modified version of the model, containing a simple implementation of denitrification and of clay fixation/release of ammonium, performed better than the original model for most treatments. We conclude that the mineralisation/immobilisation turnover in the model is not fully adequate to represent C and N dynamics. We also discuss the implementation of changes (time-varying microbial efficiency and C to N ratio; simulation of ammonium clay fixation and emissions of N2/N2O) to improve model performance. [Copyright &y& Elsevier]

Abstract: Different tree species are often associated with different soil properties. Earlier studies have shown that Norway spruce (Picea abies (L.) Karst.) and Scots pine (Pinus sylvestris L.), the two dominant tree species in Fennoscandia, often generate soils with larger carbon (C) and nitrogen (N) pools than silver birch (Betula pendula Roth.). Consequently, we hypothesised that spruce and pine would create soils with slower turnover rates than birch. To test this, C and N pools and C and N mineralisation rates were determined in different soil layers (humus, 0–10cm, 10–20cm mineral soil) at two sites with contrasting climatic conditions. One site (Tönnersjöheden) was located in the temperate zone in SW Sweden and one (Kivalo) in the north boreal zone in N Finland. At both sites, experimental plots with the three tree species had been established more than 50years before the study. Samples from the different soil layers were incubated at 15°C in the laboratory for 30days, and C and N mineralisation rates were determined. In addition, earthworm abundance was estimated at Tönnersjöheden but not at Kivalo (no sign of bioturbation). At Tönnersjöheden, soil C and N pools (gC or Nm−2) were ranked spruce>pine>birch. C mineralisation rate (mgCO2–Cg−1 Cd−1) was higher in the birch plots than in the other plots, but because of larger C pools in the spruce plots, field C mineralisation (gCO2–Cm−2 year−1) was higher for spruce than for pine and birch. Field net N mineralisation (80–90kg Nha−1 year−1) did not differ significantly between tree species, but nitrification rates (μgNO3–Ng−1 Cd−1) in the topsoil were higher in the birch plots than in the other plots. The birch plots had larger populations of earthworms and a higher degree of bioturbation than any of the coniferous plots, which probably explains the higher turnover rate of birch soil organic matter (SOM). At Kivalo, C and N soil pools were significantly larger in spruce than in birch plots, and C mineralisation rate was higher in birch and spruce humus than in pine humus. Net N mineralisation rate and annual field net N mineralisation (<4kgNha−1 year−1) were estimated to be very low, with no effect of tree species. Thus, the hypothesis of a ‘birch effect’ was supported at Tönnersjöheden, but only partly at Kivalo. The main difference seemed to be that the earthworms at Tönnersjöheden accelerated SOM decomposition under birch, whereas earthworm stimulation was negligible at Kivalo, probably because of climate-related limitations. [Copyright &y& Elsevier]

Abstract: Stabilisation of soil organic carbon (SOC) is known to be affected by chemical adsorption of organic carbon onto clay minerals and iron or aluminium hydrous-oxides. However, little information is available on the relative effects of different clay minerals in the presence or absence of different hydrous oxides. We examined organic carbon stabilisation in an incubation experiment involving kaolinitic, illitic and smectitic clays with and without added goethite. The effect of adding hydrous iron (Fe) oxides (goethite, haematite, ferrihydrite) or imogolite to illitic clay only was studied in another experiment. Carbon (C) mineralisation, measured continuously over a 144-day incubation, was significantly influenced by clay mineralogy, with higher rates observed in the presence of the kaolinitic than the illitic or smectitic clays. The presence of goethite reduced C mineralisation in kaolinitic clay treatments but did not affect C mineralisation for illitic and smectitic clay treatments. With regard to the influence of different hydrous oxides, only addition of ferrihydrite to illitic clay reduced C mineralisation. The dynamics of C mineralisation over the course of the incubation were also studied; a two-pool model consisting of slowly and rapidly decomposing C pools provided a better fit than did a one-pool model. We introduce a novel approach to a problem associated with such two-pool fits: identifying when the incubation is long enough for the fitted variables to be reliable. Based on an analysis of two-pool model variables, we identified that SOC stabilisation in our systems was brought about by a decrease in the size of decomposable pools rather than a decrease in the rates of decomposition of either pool. This implies that on sorption, a portion of the organic matter is strongly protected from decomposition. [Copyright &y& Elsevier]

Reclamation of trace element polluted soils often requires the improvement of the soil quality by using appropriate organic amendments. Low quality compost from municipal solid waste has been tested for reclamation of soils, but these materials can provide high amounts of heavy metals. Therefore, a high-quality compost, with low levels of heavy metals, produced from the main by-product of the Spanish olive oil extraction industry (“alperujo”) was evaluated for remediation of soils affected by a pyritic mine sludge. Two contaminated soils were selected from the same area: they were characterised by differing pH values (4.6 and 7.3) and total metal concentrations, which greatly affected the fractionation of the metals. Compost was applied to soil at two rates (equivalent to 48 and 72Tmha−1) and compared with an inorganic fertiliser treatment. Compost acted as an available nutrient source (C, N and P) and showed a low mineralisation rate, suggesting a slow release of nutrients and thus favouring long term soil fertility. In addition, the liming effect of the compost led to a significant reduction of toxicity for soil microorganisms in the acidic soil and immobilisation of soil heavy metals (especially Mn and Zn), resulting in a clear increase in both soil microbial biomass and nitrification. Such positive effects were clearly greater than those provoked by the mineral fertiliser even at the lowest compost application rate, which indicates that this type of compost can be very useful for bioremediation programmes (reclamation and revegetation of polluted soils) based on phytostabilisation strategies. [Copyright &y& Elsevier]

Abstract: The influence of bulking agents on organic matter (OM) stability and nitrogen (N) availability in sludge composts was investigated. Seven mixtures were composted over a 12-week period in 170L-reactors using the same sludge with different bulking agent mixtures. The OM evolution was characterised by carbon (C) and N mass balances in biochemical fractions. The evolution of OM stability and N potential availability were measured during soil incubations. The type of bulking agent had little influence on the intensity of OM stabilisation and the N availability in final composts. However, they influenced the time to reach similar OM stability and the biochemical evolution of OM. Depending on their ligno-cellulosic characteristics and a careful control of aeration, initial mixtures with high C:N ratio and rather biodegradable carbonaceous materials could favour the organisation of initially present mineral N or easily mineralisable sludge N and therefore limit NH3 volatilisation responsible for the low compost N availability measured. [ABSTRACT FROM AUTHOR]

An incubation study determined the effect of one dry–rewetting (DRW) event on the turnover of carbon (C), phosphorus (P) and nitrogen (N). Thirty-two soils were collected from different climatic regions of southern Australia, varying in soil type, land use and agronomic management history. We hypothesised that respiration and nutrient pulses are related to soil physio-chemical properties. Respiration (CO2 release) was measured intensively for 90 h after rewetting. C mineralisation ( Cmin) model fitting was used to describe the amount of mineralisable C (Co90 h) and the proportional mineralisation rate ( k). Compared to constantly moist soils, 13 soils showed increases in both Co90 h and k, indicating that DRW increased the amount of mineralisable C and the rate at which C was mineralised over the 90-h period. In 17 soils, k was increased but not Co90 h, showing an increase in C mineralisation rate but no change in the amount of mineralisable C. Two soils showed a reduction in k with no change in Co90 h, possibly due to low C contents and small microbial biomass. Only one soil exhibited no change in either Co90 h or k. Multiple linear regression analysis indicated that the magnitude of the increase in mineralisable C in response to the DRW event (∆Co90 h = Co90 h DRW − Co90 h moist) was primarily explained by clay content (39%); however, inclusion of nine soil physio-chemical properties explained more of the variation in ∆Co90 h than any of the properties alone. Five of the nine physio-chemical variables present in the multiple-regression model were related to C content or composition. Pulses in available N and P were not related to ∆Co90 h. [ABSTRACT FROM AUTHOR]

Here we test the hypotheses that 19 years of simulated pollutant N deposition increases both losses of carbon (C) and the ability of plants to access P from organic material in upland heathland. The grass, Dactylis glomerata, and the dwarf shrub, Calluna vulgaris, were grown in soil containing microbial-derived organic matter labelled with 14C and 33P. We found that both soil and root-surface phosphatase activity increased significantly in response to N deposition. We also found a significant positive relationship between root-surface phosphatase activity and 33P uptake for Calluna, but a negative relationship for Dactylis. Efflux of 14C from the microbial-derived organic matter was strongly dependent on an interaction among plant presence, plant species and N deposition. Our results show that mineralisation of C and P, and subsequent plant uptake of P from organic sources is decoupled. In our experimental conditions, stimulation of P turnover coupled with subsequent plant uptake through up-regulation of root phosphatases is little affected by N addition. However, our data indicate that root-surface phosphatases are likely to be more important for uptake of P derived from organic sources for Calluna than for Dactylis. [ABSTRACT FROM AUTHOR]

Abstract: Nitrogen (N) and carbon (C) mineralisation are triggered by pulses of water availability in arid and semi-arid systems. Intermittent streams and their associated riparian communities are obvious ‘hot spots’ for biogeochemical processes in arid landscapes where water and often C are limiting. Stream landscapes are characterized by highly heterogeneous soils that may respond variably to rewetting. We used a laboratory incubation to quantify how N and C mineralisation in rewetted soils and sediments from an intermittent stream in the semi-arid Pilbara region of north-west Australia varied with saturation level and substrate addition (as ground Eucalyptus litter). Full (100%) saturation was defined as the maximum gravimetric moisture content (%) achieved in free-draining soils and sediments after rewetting, with 50% saturation defined as half this value. We estimated rates and amounts of N mineralised from changes in inorganic N and microbial respiration as CO2 efflux throughout the incubation. In soils and sediments subject to 50% saturation, >90% of N mineralised accumulated within the first 7d of incubation, compared to only 48% when soils were fully saturated (100% saturation). Mineralisation rates and microbial respiration were similar in riparian and floodplain soils, and channel sediments. N mineralisation rates in litter-amended soils and sediments (0.73mgNkg−1 d−1) were only one-third that of unamended samples (3.04mgNkg−1 d−1), while cumulative microbial respiration was doubled in litter-amended soils, suggesting N was more rapidly immobilized. Landscape position was less important in controlling microbial activity than soil saturation when water-filled pore space (% WFPS) was greater than 40%. Our results suggest that large pulses of water availability resulting in full soil saturation cause a slower release of mineralisation products, compared to small pulse events that stimulate a rapid cycle of C and N mineralisation–immobilization. [Copyright &y& Elsevier]

Abstract: Plants link atmospheric and soil carbon pools through CO2 fixation, carbon translocation, respiration and rhizodeposition. Within soil, microbial communities both mediate carbon-sequestration and return to the atmosphere through respiration. The balance of microbial use of plant-derived and soil organic matter (SOM) carbon sources and the influence of plant-derived inputs on microbial activity are key determinants of soil carbon-balance, but are difficult to quantify. In this study we applied continuous 13C-labelling to soil-grown Lolium perenne, imposing atmospheric CO2 concentrations and nutrient additions as experimental treatments. The relative use of plant- and SOM-carbon by microbial communities was quantified by compound-specific 13C-analysis of phospholipid fatty acids (PLFAs). An isotopic mass-balance approach was applied to partition the substrate sources to soil respiration (i.e. plant- and SOM-derived), allowing direct quantification of SOM-mineralisation. Increased CO2 concentration and nutrient amendment each increased plant growth and rhizodeposition, but did not greatly alter microbial substrate use in soil. However, the increased root growth and rhizosphere volume with elevated CO2 and nutrient amendment resulted in increased rates of SOM-mineralisation per experimental unit. As rhizosphere microbial communities utilise both plant- and SOM C-sources, the results demonstrate that plant-induced priming of SOM-mineralisation can be driven by factors increasing plant growth. That the balance of microbial C-use was not affected on a specific basis may suggest that the treatments did not affect soil C-balance in this study. [Copyright &y& Elsevier]

Carbon mineralisation and plant germination and growth (Lactuca sativa seeds) tests have been performed in two soils of different properties, experimentally spiked with pentachlorophenol (PCP) or Cr (VI), in concentrations between 0. 001 and 1000 mg kg−1. The evaluation has been done considering the following parameters of carbon transformation test: soil cumulative basal respiration after 14 days incubation, substrate induced respiration after 12 h of glucose addition, and, in the plant germination and growth test: number of germinated seeds, root elongation and total biomass produced. The most sensitive assay found in our work has been carbon mineralisation test, from which the lowest toxic concentrations were obtained (especially substrate induced respiration test). In the plant germination and growth test, the measurement of root elongation has shown the best sensitiveness, followed by plant biomass and seed germination numbers. Regarding the contaminants, the highest toxicity, considering the minimum concentration with toxic effect, has been found in PCP (0. 01 mg kg−1) in C mineralisation test in the granitic soil. For Cr, the minimum concentration with toxic effect has been 0. 1 mg kg−1, also in the C mineralisation test and the granitic soil. The granitic soil has shown more vulnerability to the pollutants assayed in the respiration test, whereas the calcareous soil has shown more vulnerability in the plant germination and growth test. [Copyright &y& Elsevier]

Abstract: Indigenous soil macroinvertebrates (moth larvae, weevil larvae, earthworms) are cardinal agents of nutrient release from litter on sub-Antarctic Marion Island (47°S, 38°′E). Their populations are threatened through predation by introduced house mice, which do not prey on an introduced slug Deroceras panormitanum. A microcosm study was carried out to explore whether slugs affect rates of carbon and inorganic nutrient mineralisation from plant litter differently to an indigenous caterpillar (larva of a flightless moth Pringelophaga marioni). Caterpillars stimulated N, Ca, Mg and K mineralisation from plant litter two to five times more than slugs did, whereas the two invertebrate types stimulated C and P mineralisation to the same degree. Consequently, ratios of C:N and N:P released from the litter were different for slugs and caterpillars. Such differences might affect peat nutrient quality and ultimately the peat accumulation-decomposition balance, an important driver of ecological succession. This suggests that slugs cannot simply replace caterpillars without consequences for ecosystem structure and functioning on the island. [Copyright &y& Elsevier]

Abstract: Degradation of organic matter (OM) from organic amendments used in the remediation of metal contaminated soils leads to changes in soil chemical properties shortly after their addition, which may affect the soil metal distribution. The effects of two differing organic amendments on OM mineralisation and fractionation of heavy metals in a contaminated soil were investigated in an incubation experiment. The treatments were: control unamended soil, soil amended with fresh cow manure, and soil amended with a compost having a high maturity degree. The soil used was characteristic of the mining area at La Unión (Murcia, Spain) with 28% CaCO3 and sandy-loam texture (pH 7.7; 2602mgkg−1 Zn; 1572mgkg−1 Pb). Manure and compost C-mineralisation after 56 days (24% and 3.8%, respectively) were below values reported previously for uncontaminated soils. Both amendments favoured Zn and Pb fixation, particularly the manure. Mn solubility increased at the beginning of the experiment due to a pH effect, and only Cu solubility increased through organic matter chelation in both amended soils. [Copyright &y& Elsevier]

Abstract: The effects of humic acids (HAs) extracted from two different organic materials on the distribution of heavy metals and on organic-C mineralisation in two contaminated soils were studied in incubation experiments. Humic acids isolated from a mature compost (HAC) and a commercial Spaghnum peat (HAP) were added to an acid soil (pH 3.4; 966mgkg−1 Zn and 9229mgkg−1 Pb as main contaminants) and to a calcareous soil (pH 7.7; 2602mgkg−1 Zn and 1572mgkg−1 Pb as main contaminants) at a rate of 1.1g organic-C added per 100g soil. The mineralisation of organic-C was determined by the CO2 released during the experiment. After 2, 8 and 28 weeks of incubation the heavy metals of the soils were fractionated by a sequential extraction procedure. After 28 weeks of incubation, the mineralisation of the organic-C added was rather low in the soils studied (<8% of TOC in the acid soil; <10% of TOC in the calcareous soil). Both humic acids caused significant Zn and Pb immobilisation (increased proportion of the residual fraction, extractable only with aqua regia) in the acid soil, while Cu and Fe were slightly mobilised (increased concentrations extractable with 0.1M CaCl2 and/or 0.5M NaOH). In the calcareous soil there were lesser effects, and at the end of the experiment only the fraction mainly related to carbonates (EDTA-extractable) was significantly increased for Zn and decreased for Fe in the humic acids treated samples. However, HA–metal interactions provoked the flocculation of these substances, as suggested by the association of the humic acids with the sand fraction of the soil. These results indicate that humic acid-rich materials can be useful amendments for soil remediation involving stabilisation, although a concomitant slight mobilisation of Zn, Pb and Cu can be provoked in acid soils. [Copyright &y& Elsevier]

Abstract: The anecic earthworm Lumbricus terrestris L. is known to strongly affect organic matter transformation and soil development in temperate ecosystems. Processes in the gut of the earthworm play an important role where sand grains contribute to the grinding of leaf litter in the muscular gizzard. To investigate effects of sand and litter availability and earthworm gut passage on carbon and nitrogen mineralisation two experiments were set up, one with beech forest soil and beech litter, the other with arable soil and rye litter, thereby exploring the effects of agricultural management and litter type on mobilisation and stabilisation of organic matter. Three different sand concentrations were tested in the forest soil: without, with 25% and with 50% sand (dry weight). In the arable soil only treatments without and with 25% sand were established. The soil was taken from a beech forest on limestone and from a long-term agricultural experiment. Earthworms were fed fragmentised beech or rye litter (&#60;4 mm), or were kept without litter. Earthworm casts produced during 65 days were placed in microcosms and incubated at 20 °C for 280 days. CO2 production and mineral nitrogen in leaching water were measured at regular intervals. Earthworms lost more mass in arable than in forest soil; even though in arable soil the earthworms produced two times more casts. Litter availability reduced burrow construction. Casts were more enriched in carbon and nitrogen if litter was available. Leaching of Nmin from casts of L. terrestris strongly exceeded that of the corresponding soil treatments in the arable soil but not in the forest soil. In earthworm casts decomposition of rye litter was strongly increased, in particular early in the experiment. In contrast, the decomposition of beech litter was reduced initially and stimulated later. The addition of sand stimulated carbon mineralisation in both organic matter in soil and enclosed in earthworm casts. In soils with high clay content (forest soil) the stimulating effect of sand was less pronounced than in soils with low clay content (arable soil). Overall, except in earthworm casts of the forest soil without litter, cumulative CO2 production exceeded that in the corresponding soil suggesting that in earthworm casts mobilisation rather than stabilisation processes prevail. [Copyright &y& Elsevier]

To accurately predict the potential environmental benefits of energy crops, the sequestration of carbon in soil needs to be quantified. The aim of this study was to investigate the mineralisation rate of the perennial C4 grass Miscanthus giganteus and Miscanthus-derived soil organic matter under contrasting nitrogen supply. Soils were collected from sites where Miscanthus had been grown for 11 and 18 years, respectively, and where a C3-grass (Lolium spp.) had been grown for 7 years. The soils were incubated for 4 months at two levels of soil inorganic nitrogen with or without dead root material of Miscanthus. Addition of root material (residues) increased carbon mineralisation of indigenous organic matter when no nitrogen was added. Added inorganic nitrogen decreased carbon mineralisation in all soils. Nitrogen addition did not affect carbon mineralisation of the residues. Using the 13C fraction to calculate the proportion of respiratory CO2 derived from Miscanthus showed that nitrogen addition decreased carbon mineralisation in soils, but it did not affect carbon mineralisation of the residues. Nitrogen mineralisation was highest in the C3 grass soil without added residues. Nitrification decreased pH, especially in the treatments where nitrogen was added. The Miscanthus-derived organic matter is at least as stable as C3 grassland-derived organic matter. Furthermore, the turnover time of the organic matter increases with time under Miscanthus cultivation. The CENTURY soil organic matter sub-model was used to simulate the organic matter decomposition in the experiment. Carbon mineralisation was accurately simulated but there were unexplained discrepancies in the simulation of the δ13C in the respiration from the treatment with residues. The δ13C in respiration did not decrease with time as predicted, indicating that lignin accumulation did not influence the measurements. [Copyright &y& Elsevier]

A fraction of the C of residues incorporated into soil diffuses into the adjacent soil where it is eventually mineralised by microorganisms. Our aim was to quantify the contribution of this adjacent soil to the overall mineralisation of residue-C. For this, we incorporated two different residues labelled with 13C, with contrasting biochemical characteristics, namely mature wheat straw and young rye leaves, in soil cores. When 15% mineralisation of residue-C was measured for both residues, we separated a particulate fraction (the residues), the adjacent soil (4–5 mm thick) and a distant soil fraction, and incubated them separately for 5 h. We found that 76% of the mineralised wheat straw-C came from the particulate fraction and 23% from the soil adjacent to the residues. For rye leaves, 67% of the evolved CO2 came from the particulate fraction and 33% from the adjacent soil. It showed that the adjacent soil had a significant role in the mineralisation of carbon from the residues, even if the main source of residue-derived CO2 was the particulate fraction itself. The functional importance of the soil adjacent to the residues increased with the amount of soluble organic compounds that had been leached from the residue into the adjacent soil, suggesting a strong interaction between the initial quality of the crop residue and the resulting spatial heterogeneity of the decomposing microorganisms and C within the soil. [Copyright &y& Elsevier]

Wood ants ( Formica rufa group) often bring large quantities of conifer resin to their mounds. The aim of this study was to test the hypothesis that the resin acts as a fungicide and thereby reduces C and N mineralisation. Two laboratory incubation experiments were carried out using two different materials: F/H layer from a Scots pine ( Pinus sylvestris) stand and mixed litter from Scots pine and Norway spruce ( Picea abies) stands. We estimated the effects of resin addition on fungal biomass and on the rates of C and N mineralisation. Addition of resin to the F/H material caused an increase in fungal biomass and C mineralisation, whereas N mineralisation decreased. Addition of resin to litter material did not significantly affect fungal biomass or C and N mineralisation. The results indicate that rather than having a fungicidal effect, resin acts as a C source that increases C mineralisation (mainly from the resin itself) and decreases net N mineralisation. The latter factor might be important in preventing plants dependent on inorganic N from invading and covering the ant mounds. [ABSTRACT FROM AUTHOR]