Role of Nanoclays in Carbon stabilization in Andisols and Cambisols

Greenhouse gas (GHG) emissions and their consequent effect on global warming are an issue of global environmental concern. Increased carbon (C) stabilization and sequestration in soil organic matter (SOM) is one of the ways to mitigate these emissions. Here we evaluated the role of nanoclays isolated from soil on C stabilization in both a C rich Andisols and C depleted Cambisols. Nanoclays were analyzed for size and morphology by transmission electron microscopy, for elemental composition and molecular composition using pyrolysis-GC/MS. Moreover, nanoclays were treated with H2O2 to isolate stable SOM associated with them. Our result showed better nanoclay extraction efficiency and higher nanoclay yield for Cambisol compared to Andisols, probably related to their low organic matter content. Nanoclay fractions from both soils were different in size, morphology, surface reactivity and SOM content. Nanoclays in Andisols sequester around 5-times more C than Cambisols, and stabilized 6 to 8-times more C than Cambisols nanoclay after SOM chemical oxidation. Isoelectric points and surface charge of nanoclays extracted from the two soils was very different. However, the chemical reactivity of the nanoclay SOM was similar, illustrating their importance for C sequestration. Generally, the precise C stabilization mechanisms of both soils may be different, with nanoscale aggregation being more important in Andisols. We can conclude that independent of the soil type and mineralogy the nanoclay fraction may play an important role in C sequestration and stabilization in soil-plant systems

Reconstructing genomes of carbon monoxide oxidisers in volcanic deposits including members of the class Ktedonobacteria

Microorganisms can potentially colonise volcanic rocks using the chemical energy in reduced gases such as methane, hydrogen (H2) and carbon monoxide (CO). In this study, we analysed soil metagenomes from Chilean volcanic soils, representing three different successional stages with ages of 380, 269 and 63 years, respectively. A total of 19 metagenome-assembled genomes (MAGs) were retrieved from all stages with a higher number observed in the youngest soil (1640: 2 MAGs, 1751: 1 MAG, 1957: 16 MAGs). Genomic similarity indices showed that several MAGs had amino-acid identity (AAI) values >50% to the phyla Actinobacteria, Acidobacteria, Gemmatimonadetes, Proteobacteria and Chloroflexi. Three MAGs from the youngest site (1957) belonged to the class Ktedonobacteria (Chloroflexi). Complete cellular functions of all the MAGs were characterised, including carbon fixation, terpenoid backbone biosynthesis, formate oxidation and CO oxidation. All 19 environmental genomes contained at least one gene encoding a putative carbon monoxide dehydrogenase (CODH). Three MAGs had form I coxL operon (encoding the large subunit CO-dehydrogenase). One of these MAGs (MAG-1957-2.1, Ktedonobacterales) was highly abundant in the youngest soil. MAG-1957-2.1 also contained genes encoding a [NiFe]-hydrogenase and hyp genes encoding accessory enzymes and proteins. Little is known about the Ktedonobacterales through cultivated isolates, but some species can utilise H2 and CO for growth. Our results strongly suggest that the remote volcanic sites in Chile represent a natural habitat for Ktedonobacteria and they may use reduced gases for growth

Carbon storage and DNA absorption in allophanic soils and paleosols

Andisols and andic paleosols dominated by the nanocrystalline mineral allophane sequester large amounts of carbon (C), attributable mainly to its chemical bonding with charged hydroxyl groups on the surface of allophane together with its physical protection in nanopores within and between allophane nanoaggregates. C near-edge X-ray absorption fine structure (NEXAFS) spectra for a New Zealand Andisol (Tirau series) showed that the organic matter (OM) mainly comprises quinonic, aromatic, aliphatic, and carboxylic C. In different buried horizons from several other Andisols, C contents varied but the C species were similar, attributable to pedogenic processes operating during developmental upbuilding, downward leaching, or both. The presence of OM in natural allophanic soils weakened the adsorption of DNA on clay; an adsorption isotherm experiment involving humic acid (HA) showed that HA-free synthetic allophane adsorbed seven times more DNA than HA-rich synthetic allophane. Phosphorus X-ray absorption near-edge structure (XANES) spectra for salmonsperm DNA and DNA-clay complexes indicated that DNA was bound to the allophane clay through the phosphate group, but it is not clear if DNA was chemically bound to the surface of the allophane or to OM, or both. We plan more experiments to investigate interactions among DNA, allophane (natural and synthetic), and OM. Because DNA shows a high affinity to allophane, we are studying the potential to reconstruct late Quaternary palaeoenvironments by attempting to extract and characterise ancient DNA from allophanic paleosol

Adding worms during composting of organic waste with red mud and fly ash reduces CO 2 emissions and increases plant available nutrient contents

Alkaline industrial wastes such as red mud and fly ash are produced in large quantities. They may be recycled as bulking agent during composting and vermicomposting, converting organic waste into soil amendments or plant growth media. The aim of this study was to assess the microbial parameters, greenhouse gas emissions and nutrient availability during composting and vermicomposting of household waste with red mud and fly ash 15% (dry weight). CO2, CH4 and N2O emissions were monitored during 6 months in controlled laboratory conditions and microbial biomass and phospholipid acids, N and P availability were analysed in the end-products.Higher CO2 emissions were observed during vermicomposting compared to composting. These emissions were decreased by red mud addition, while fly ash had no effect. Nitrate (NO3-N) content of the end-products were more affected by worms than by alkaline materials, while higher ammonium (NH4-N) contents were recorded for composts than vermicomposts. Red mud vermicompost showed higher soluble P proportion than red mud compost, suggesting that worm presence can counterbalance P adsorption to the inorganic matrix. Final composts produced with red mud showed no harmful heavy metal concentrations. Adding worms during composting thus improved the product nutrient availability and did not increase metal toxicity. From a practical point of view, this study suggests that for carbon stabilisation and end-product quality, the addition of red mud during composting should be accompanied by worm addition to counterbalance negative effects on nutrient availability

Chemical nature of residual phosphorus in Andisols

International audienceSequential fractionation has been widely used to study the nature and dynamics of soil P. Residual P - the recalcitrant P fraction remaining after sequential extraction with alkali and acid reagents - often constitutes the majority of the soil P, yet its nature and bioavailability is poorly understood. The objective of this study was to isolate, quantify, and characterize residual P following Hedley fractionation in a range of Andisols under grazed pasture by 31P nuclear magnetic resonance (NMR) spectroscopy. Residual P accounted for 45-63% of the total soil P, of which 53-77% was inorganic orthophosphate. Organic P accounted for 21-42% of the residual P, the majority of which occurred as phosphomonoesters including myo- (16% of the residual P) and scyllo-inositol hexaldsphosphate (10% of the residual P). No phosphodiesters were detected in the residual fraction. We conclude that residual P in Andisols consists of a mixture of inorganic P and organic P. Our findings provide the basis for the development of new approaches to improve P use efficiency in agriculture

Fertilizer effects on phosphorus fractions and organic matter in Andisols

Andisols are characterized by a high phosphorus (P) fixation capacity, which is a limiting factor for plant production. Continuous application of P fertilizer may result in an accumulation of P associated with soil organic matter (SOM), which further acts to reduce the availability of the added P. The objectives of this study were (1) to evaluate the impact of P fertilizer inputs on the quantities and chemical forms of P, and (2) to investigate relationships between P forms SOM and land use. Topsoil (0-20 cm) and subsoil (20-40 cm) samples were taken from two Andisols series under grassland and arable cropping. Soil P forms were determined using sequential fractionation, while SOM analysis involved a combination of C-13 nuclear magnetic resonance (NMR) spectroscopy and pyrolysis-GC-mass spectrometry. Fertilization increased total P, total organic P, organic carbon, and inorganic P fractions, mainly in arable soils. Labile P was higher in grassland (3% of total P) than in arable soils (1% of total P). A clear effect of fertilization was observed on organic matter compounds measured by pyrolysis in both soil depths. Interestingly, the polysaccharide-derived compounds increased in fertilized soils and lipid-derived compounds decreased. Thus fertilization principally affected labile P and labile SOM forms, whereas recalcitrant forms of P and SOM remained unchanged

Addition of nanoparticles and biochar to agricultural waste composting: effects on composting process and CO2-CH4 emissions

Comunicación oral presentada en el ISMOM 2019 - 8th International Symposium on Interactions of Soil Minerals with Organic Components and Microorganisms: (Abstract number: A 5.21), 23-28 june, Sevilla (Spain)Little is known about the impact of inorganic nanoparticles as additives in composting systems. The objective of this research was to evaluate the effects of iron oxide/halloysite nanoparticles and biochar as additives in the main physical and chemical properties and greenhouse gas (GHG) emissions of agricultural waste composting. Wheat straw and beef manure were mixed (2:1 w/w; C/N: 25) and co-composted with iron oxide (CFe) and halloysite (CHa) nanoparticles (2% w/w) oat-biochar (CB) (7% w/w) and their combination (CBFe CBHa). Changes in pH and EC organic matter (OM) losses NH4-NO3 concentration C/N and E4/E6 ratio and the emissions of CO2 and CH4 were analyzed. Additionally the initial mixtures and end-products were characterized by nuclear magnetic resonance (13C NMR). Additives slightly affected pH (final pH about 8.0) and increased the electroconductivity of mixtures. Nanoparticles biochar and their combination reduced the OM and C losses (about 15%) compared to control without additives. A decrease of C/N ratio between initial and end-products were also observed in all treatments and lower differences were observed in treatments with additives. Nitrate concentration increased as composting progressed. CHa showed the higher mean concentration of NO3 (2500 mg kg-1) and NH4 (120 mg kg-1). Conversely CBFe and CBHa showed the lower mean concentration of NH4 (60 mg kg-1). Nanoparticles significantly decreased the final E4/E6 ratio (<6) and the addition of biochar and its combination with nanoparticles increased the aromaticity (twice) the alkyl-C/O alkyl-C ratio and the hydrophobicity which are parameters associated to stabilized end-products. Clear relative diminution of O alkyl-C region (50%) associated to carbohydrates was observed in treatments with additives suggesting an active composting process. Furthermore the addition of biochar (CB) significantly decreased the mean emission of both CO2 (~400 g CO2 m2 d-1) and CH4 (4.5 g CH4 m2 d-1) during the process. These results suggest that the addition of iron oxide/halloysite nanoparticles biochar and their combination as co-composting additives had important effects on composting process GHG emissions and chemical composition of the end-products.FONDECYT/CONICYT Project N° 3170677

Influence of saprophytic fungi and inorganic additives on enzyme activities and chemical properties of the biodegradation process of wheat straw for the production of organo-mineral amendments

Cellulose and lignin as main components of crop residues have a significant influence on composting operations and composition of the final products. Both are strongly associated, and lignin can be considered an important barrier during the biodegradation process of lignocellulosic materials. Saprophytic fungi are efficient lignin degraders due to their complex enzymatic system. Therefore, the influence of the inoculation of saprophytic fungi (Coriolopsis rigida, Pleurotus ostreams, Trichoderma harzianum and Trametes versicolor) and the supply of inorganic additives (Al2O3, Fe2O3 and allophanic soil) that promote the stabilization of carbon (C), were analyzed in the biodegradation of wheat straw (WS). The activity of Laccase (LAC), manganese peroxidase (MnP) and beta-glucosidase and changes in temperature, pH and E-4/E-6 ratio were analyzed in a biodegradation process of 126 days. The activity of LAC, MnP and the E-4/E-6 ratio were significantly influenced and increased (enzymes) by fungi species, inorganic additives, and time of inorganic material addition, as well as their interactions (p < 0.05). The WS inoculated with T. versicolor showed the highest average activities for LAC, MnP and beta-glucosidase (2000, 220 UL-1 and 400 mu mol pNP g(-1) h(-1) respectively). Furthermore, the addition of Al2O3 and Fe2O3 increased all the activities regarded to the decomposition of WS and influenced the changes associated with the stabilization of OM in composted WS. In conclusion, the inoculation of WS with T. versicolor in combination with metal oxides improved the enzyme related to the biodegradation process of WS favorizing its stabilization in the medium time, which is of importance in the composting of residues with high C/N ratio

Influence of inorganic additives on wheat straw composting: Characterization and structural composition of organic matter derived from the process

10 páginas.- 3 figuras.- 6 tablas.- referencias.-Metallic oxides and clay minerals have gained increasing interest as additives of composting due to their influence in greenhouse gas emissions reduction and their effectivity in the stabilization of carbon both in compost and soils, leading to a cleaner compost production and potentially C sequestrant amendments. In this study, wheat straw (WS) was co-composted with iron oxide and allophanic soil and their influence on WS composting and composition of the end-products was evaluated. WS compost and their humic like-substances (HS) fraction were characterized by chemical and spectroscopic analyzes. After 126 days of process, the elemental composition showed slight differences of the N content for compost and HS, where the C/N atomic ratio tended to decrease relative to the initial material (WS; ~130). This trend was more pronounced in the HS from co-composted treatments (<30). The addition of inorganic materials increased the total acidity and phenolic-OH group contents (~15 and 14 mEq g−1 respectively, iron oxide treatment) relative to the treatment without inorganic additives. Nevertheless, the FTIR and solid-state 13CNMR spectroscopy barely support the wet chemical analysis and revealed a similar final composition between all the studied compost treatments. These results suggest that the incorporation of these materials as compost additives had no major effect on the spectroscopic features of the end-products, however, critical changes of the properties such as the extractability, functionality and composition of HS were revealed by traditional methods. In conclusion, the supply of metal oxides and clays could impact the aerobic composting of WS favorizing the stabilization of certain C pools and adsorptive properties of the end-products, that is of importance in production of amendments suitable for being used in degraded and contaminated soils. Nevertheless, under the experimental conditions of our research C stabilization apparently depends of other mechanisms that still need to be elucidate.The authors thank the Comisión Nacional de Investigación Científica y Tecnológica (CONICYT-Chile), for the economic support through the program CONICYT/FONDECYT/1170264 and CONICYT/FONDAP/15130015 (P. Cornejo). H. Knicker thanks the Ministerio de Ciencia, Innovacion y Universidades of Spain and the European Regional Development Fund for financial support through the project CGL2015-64811-P. J. Medina and M. Calabi-Floody thanks CONICYT for the financial support through the CONICYT/FONDECYT/3170677 grant and CONICYT/FONDECYT/11150555 grant, respectively. M. Antilén and P. Cornejo also thank CONICYT for the economic support through the project CONICYT-PIA Rings in Mining Topics ACM170002.Peer reviewe