Lignin degradation during a laboratory incubation followed by 13C isotope analysis

Recent in situ ¹³C studies suggest that lignin is not stabilised in soil in its polymerised form. However, the fate of its transformation products remains unknown. The objective of the present research was to provide the first comprehensive picture of the fate of lignin-derived C across its transformations processes: (1) C remaining as undecomposed lignin molecules, (2) C in newly formed humic substances, i.e. no longer identifiable as lignin-polymer C, (3) C in microbial biomass, (4) C mineralised as CO₂, and (5) dissolved organic C. To achieve this objective, we designed an incubation experiment with ¹³C-labelled lignin where both elementary and molecular techniques were applied. Lignin was isolated from ¹³C labelled maize plants (¹³C-MMEL) and incubated in an agricultural soil for 44 weeks. Carbon mineralisation and stable isotope composition of the released CO₂ were monitored throughout the incubation. Microbial utilisation of ¹³C-MMEL was measured seven times during the experiment. The turnover rate of the lignin polymer was assessed by ¹³C analysis of CuO oxidation products of soil lignin molecules. After 44 incubation weeks, 6.0% of initial ¹³C-MMEL carbon was mineralised, 0.8% was contained in the microbial biomass, and 0.1% was contained in dissolved organic C form. The compound-specific ¹³C data suggest that the remaining 93% were overwhelmingly in the form of untransformed lignin polymer. However, limited transformation into other humic substances potentially occurred, but could not be quantified because the yield of the CuO oxidation method proved somewhat variable with incubation time. The initial bacterial growth yield efficiency for MMEL was 31% and rapidly decreased to plateau of 8%. A two-pool first-order kinetics model suggested that the vast majority (97%) of MMEL lignin had a turnover time of about 25 years, which is similar to field-estimated turnover times for soil-extractable lignin but much longer than estimated turnover times for fresh plant-residue lignin. We conclude that natural lignin structures isolated from plants are rather unreactive in soil, either due to the lack of easily available organic matter for co-metabolism or due to enhanced adsorption properties. The data also suggest that fairly undecomposed lignin structures are the main reservoir of lignin-derived C in soils.     

Lignin and cellulose degradation and nitrogen dynamics during decomposition of three leaf litter species in a Mediterranean ecosystem

Cellulose and lignin degradation dynamics was monitored during the leaf litter decomposition of three typical species of the Mediterranean area, Cistus incanus L., Myrtus communis L. and Quercus ilex L., using the litter bag method. Total N and its distribution among lignin, cellulose and acid-detergent-soluble fractions were measured and related to the overall decay process. The litter organic substance of Cistus and Myrtus decomposed more rapidly than that of Quercus. The decay constants were 0.47 year⁻¹, 0.75 year⁻¹ and 0.30 year⁻¹ for Cistus, Myrtus and Quercus, respectively. Lignin and cellulose contents were different as were their relative amounts (34 and 18%, 15 and 37%, 37 and 39% of the overall litter organic matter before exposure, for Cistus, Myrtus and Quercus, respectively). Lignin began to decrease after 6 and 8 months of exposure in Cistus and Myrtus, respectively, while it did not change significantly during the entire study period in Quercus. The holocellulose, in contrast, began to decompose in Cistus after 1 year, while in Quercus and Myrtus immediately. Nitrogen was strongly immobilized in all the litters in the early period of decay. Its release began after the first year in Cistus and Myrtus and after 2 years of decomposition in Quercus. These litters still contained about 60, 20 and 90% of the initial nitrogen at the end of the experiment (3 years). Prior to litter exposure nitrogen associated with the lignin fraction was 65, 54 and 37% in Cistus, Myrtus and Quercus, while that associated with the cellulose fraction was 30, 24 and 28%. Although most of the nitrogen was not lost from litters, its distribution among the litter components changed significantly during decomposition. In Cistus and Myrtus the nitrogen associated with lignin began to decrease just 4 months after exposure. In Quercus this process was slowed and after 3 years of decomposition 8% of the nitrogen remained associated with lignin or lignin-like substances. The nitrogen associated with cellulose or cellulose-like substances, in contrast, began to decrease from the beginning of cellulose decomposition in all three species. At the end of the study period most of the nitrogen was not associated to the lignocellulose fraction but to the acid-detergent-soluble substance (87, 88 and 84% of the remaining litter nitrogen).     

基于城市固废堆肥的尾矿库表土植物修复研究

采用盆栽试验的方法研究了城市固废堆肥(MSWC)结合外来植株果园草[Dactylis glomerata L.(D.glomerata)]和本地植株西班牙欧石楠[Erica australis L.(E.australis)]对葡萄牙S.Domingos矿区尾矿库表土植被恢复和土壤酶活性的影响.结果表明,MSWC处理表...     

Stable carbon isotope ratios of water-extractable organic carbon affected by application of rice straw and rice straw compost during a long-term rice experiment in Yamagata,Japan

ABSTRACT

Hot-water- and water-extractable organic matter were obtained from soil samples collected from a rice paddy 31 years after the start of a long-term rice experiment in Yamagata, Japan. Specifically, hot-water-extractable organic carbon and nitrogen (HWEOC and HWEON) were obtained by extraction at 80°C for 16 h, and water-extractable organic carbon and nitrogen (WEOC and WEON) were obtained by extraction at room temperature. The soil samples were collected from surface (0–15 cm) and subsurface (15–25 cm) layers of five plots that had been treated with inorganic fertilizers alone or with inorganic fertilizers plus organic matter, as follows: PK, NPK, NPK plus rice straw (RS), NPK plus rice straw compost (CM1), and NPK plus a high dose of rice straw compost (CM3). The soil/water ratio was 1:10 for both extraction temperatures. We found that the organic carbon and total nitrogen contents of the bulk soils were highly correlated with the extractable organic carbon and nitrogen contents regardless of extraction temperature, and the extractable organic carbon and nitrogen contents were higher in the plots that were treated with inorganic fertilizers plus organic matter than in the PK and NPK plots. The HWEOC and WEOC δ¹³C values ranged from ?28.2% to ?26.4% and were similar to the values for the applied rice straw and rice straw compost. There were no correlations between the HWEOC or WEOC δ¹³C values and the amounts of HWEOC or WEOC. The δ¹³C values of the bulk soils ranged from ?25.7% to ?23.2% and were lower for the RS and CM plots than for the PK and NPK plots. These results indicate that HWEOC and WEOC originated mainly from rice plants and the applied organic matter rather than from the indigenous soil organic matter. The significant positive correlations between the amounts of HWEOC and HWEON and the amount of available nitrogen (P < 0.001) imply that extractable organic matter can be used as an index for soil fertility in this long-term experiment. We concluded that the applied organic matter decomposed more rapidly than the indigenous soil organic matter and affected WEOC δ¹³C values and amounts.     

Soil degradation caused by a high-intensity rainfall event: Implications for medium-term soil sustainability in Burgundian vineyards

The purpose of this paper is to provide a sediment-flux quantification in a vineyard context (Vosne-Romanée, Burgundy, France) where medium-term soil budget and sustainability are controlled by complex interactions between natural processes (rill erosion) and anthropogenic processes (earth supply transferred back into the rills by the winegrowers).     

Microbial communities responsible for the decomposition of rice straw compost in a Japanese rice paddy field determined by phospholipid fatty acid (PLFA) analysis

To identify the microbial communities responsible for the decomposition of rice straw compost in soil during the rice cultivation period, phospholipid fatty acid (PLFA) composition of rice straw compost was determined by periodically sampling the compost from a Japanese rice field under flooded conditions. About 21% of the compost was decomposed within a period of 3 months. The total amount of PLFAs, as an indicator of microbial biomass, was significantly lower under drained conditions than under flooded conditions and was relatively constant during the flooding period. This indicates that the microbial biomass in the compost samples did not increase during the gradual decomposition of rice straw compost under flooded conditions. The proportion of branched-chain PLFAs (biomarker of Grampositive and anaerobic Gram-negative bacteria) slightly decreased during the early period after placement, and increased gradually afterwards. Among the branched-chain PLFAs, i15:0, ail5:0, i16:0 and i17:0 PLFAs predominated and their proportions increased gradually except for i16:0. The proportion of straight mono-unsaturated PLFAs (biomarker of Gramnegative bacteria) was almost constant throughout the period, and 18:1ω9 and 18:1ω7 PLFAs predominated. The proportion of straight poly-unsaturated PLFAs as a biomarker of eukaryotes including fungi was also constant throughout the period, except for a decrease under drained conditions. Straight poly-unsaturated PLFAs consisted mainly of 18:2ω6c PLFA. Therefore, these results suggest that the proportions of Gram-positive and anaerobic Gram-negative bacteria increased during the decomposition of rice straw compost in flooded paddy field. Statistical analyses enabled to divide PLFA patterns of microbiota in the rice straw compost into two groups, one group consisting of rice straw compost samples collected before mid-season drainage and the other of samples collected after mid-season drainage. Small squared distances among samples in cluster analysis indicated that the community structure of microbiota was similar to each other as a whole. These results suggest that the microbial communities changed gradually during the period of placement, and that mid-season drainage may have affected the community structure of microbiota. Principal component analysis of the PLFA composition suggested that the succession of microbiota along with the decomposition in flooded soil was similar between rice straw compost and rice straw and that the changes in the community structure during the decomposition in flooded soil were more conspicuous for rice straw than for rice straw compost.     

The nutrient release rate accounts for the effect of organic matter type on soil microbial carbon use efficiency of a Pinus tabulaeformis forest in northern China

Journal of Soils and Sediments - Microbial carbon use efficiency (CUE) greatly controls the magnitude of soil organic carbon turnover. This study was conducted to estimate the CUE with the...     

Influence of mixtures of acenaphthylene and benzo[a]anthracene on their degradation by Pleurotus ostreatus in sandy soil

Purpose

Polycyclic aromatic hydrocarbons (PAHs) are a class of organic compounds commonly found as soil contaminants. Fungal degradation is considered as an environmentally friendly and cost-effective approach to remove PAHs from soil. Acenaphthylene (Ace) and Benzo[a]anthracene (BaA) are two PAHs that can coexist in soils; however, the influence of the presence of each other on their biodegradation has not been studied. The biodegradation of Ace and BaA, alone and in mixtures, by the white rot fungus Pleurotus ostreatus was studied in a sandy soil.

Materials and methods

Experimental microcosms containing soil spiked with different concentrations of Ace and BaA were inoculated with P. ostreatus. Initial (t ₀) and final (after 15 days of incubation) soil concentrations of Ace and BaA were determined after extraction of the PAHs.

Results and discussion

P. ostreatus was able to degrade 57.7% of the Ace in soil spiked at 30 mg kg^?1 dry soil and 65.8% of Ace in soil spiked at 60 mg kg^?1 dry soil. The degradation efficiency of BaA by P. ostreatus was 86.7 and 77.4% in soil spiked with Ace at 30 and 60 mg kg^?1 dry soil, respectively. After 15 days of incubation, there were no significant differences in Ace concentration between soil spiked with Ace and soil spiked with Ace + BaA, irrespective of the initial soil concentration of both PAHs. There were also no differences in BaA concentration between soil spiked with BaA and soil spiked with BaA + Ace.

Conclusions

The results indicate that the fungal degradation of Ace and BaA was not influenced by the presence of each other’s PAH in sandy soil. Bioremediation of soils contaminated with Ace and BaA using P. ostreatus is a promising approach to eliminate these PAHs from the environment.     

Analysis of nitrate ion in nettle (Urtica dioica L.) by ion-pair chromatographic method on a C30 stationary phase

Nitrate ion is a frequent pollutant not only in soil and natural water resources but in vegetables and foods as well. In our study we focused on nettle due to its increased ability to accumulate nitrate ions. A new, simple method for the separation and determination of nitrate ion based on reversed-phase ion-pair chromatography has been elaborated. A new four-step sample pretreatment method enables the precipitation of proteins and oxidative degradation of compounds that may disturb the identification of the nitrate ion: (1) extraction of the total nitrate content, (2) precipitation of proteins with acetonitrile, (3) oxidative degradation of the organic contaminants with H2O2, (4) evaporation of the solvent and taking up of the residue in water. The chromatographic separations were carried out on a high-density C30 stationary phase under isocratic conditions. The optimal mobile-phase composition was 10% (v/v) acetonitrile and 90% (v/v) 20 mmol L(-1) phosphate buffer, containing 2 mmol of tetrabutylammonium hydroxide at pH 6.0. The method could also be used for the separation of IO3(-), SeO3(2-), BrO3(-), NO2(-), Br-, SeO4(2-), and I- ions. The validated method is sensitive (the detection limit is 0.18 ng of nitrate ion). The method is linear in a high concentration range (0.031-30.66 microg mL(-1)). Recoveries varied between 98% and 103%. Reproducibility of the elaborated sample pretreatment method showed 1.54%. The method can be used for the determination of nitrate ion from different plants.     

Impact of cultivation and sugar-cane green trash management on carbon fractions and aggregate stability for a Chromic Luvisol in Queensland, Australia

Technological advances in sugar-cane harvesting and processing is bringing about rapid changes in production systems which could impact on soil physical conditions. An increasing incidence of soil structural decline and depletion of soil carbon levels has increased the risk of soil erosion and crop yield reductions. Soil carbon (C) and aggregate stability were studied on a sugar-cane (Saccharum officinarum L.) green trash blanket trial that had been established on a Chromic Luvisol soil at Mackay, Qld, Australia in 1992. The experiment consisted of blocks with two blocks being harvested early and the remaining two blocks harvested late in the crushing season. Within each block, treatment combinations of trash burnt or green trash blanket, which are either cultivated between rows or not cultivated after harvest, were included. Cropping and cultivation of the soil reduced the different C fractions in the surface 0–100 mm layer by 66–67% when compared to an adjacent uncropped reference soil. The labile C (C_L) concentration was 11% lower in the burnt treatment compared to the trash returned treatment but the opposite was found for total C (C_T). After four years, the no cultivation treatment had higher concentrations of all C fractions measured, compared to the cultivated treatment. When compared to the uncropped reference soil, cropping resulted in marked reductions in aggregate mean weight diameter (MWD) and aggregates >250 μm and an increase in aggregates <125 μm determined by both immersion and tension wetting. The return of the green trash resulted in a 30% greater MWD and a 28% increase in aggregates >250 μm and an 18% reduction in aggregates <125 μm compared to the burnt treatment when immersion wetting was used. Four years of cultivation reduced the MWD, as determined by immersion wetting, by 26% compared to the no cultivation treatment. No significant correlations were found between any measured C fraction and aggregate stability. This study indicates that sustainable sugar-cane cropping systems will likely be those where cultivation is kept to a minimum and trash is retained in the system.     

Implications of beta-mercaptoethanol in relation to folate stability and to determination of folate degradation kinetics during processing: a case study on [6S]-5-methyltetrahydrofolic acid

The effect of beta-mercaptoethanol (0-2%) addition to thermally and/or pressure-treated samples on [6S]-5-methyltetrahydrofolate was studied. Degradation of [6S]-5-methyltetrahydrofolate during both thermal and pressure treatments was mainly caused by oxidation, and the oxidized folates could be partly/completely reduced by beta-mercaptoethanol. The addition of beta-mercaptoethanol (2%) to the thermally and pressure-treated samples overestimated the "actual" stability of [6S]-5-methyltetrahydrofolate and misled the obtained kinetic information.     

A study of mole drainage with simplified cultivation for autumn-sown crops on a clay soil. 5. Losses of nitrate-N in surface run-off and drain water

Direct drilling of autumn-sown cereal crops reduced the loss of nitrate in drainage. Losses of nitrate nitrogen in water draining from arable land have been measured for 4 seasons, 1980–1984. The field experiment was on a mole-drained clay soil in southern England. Autumn-sown cereal crops were established by direct drilling or after ploughing and traditional seed-bed preparation. Losses ranged from 3 to 75 kg N ha⁻¹ year⁻¹, with an average of 34 kg N ha⁻¹ year⁻¹. Most of the loss (about 90%) was removed via the mole-drain system. Measured loss of nitrate from the direct-drilled soil was 76% (range 48–89%) of that lost from the ploughed soil. Mole drains apparently increased loss of nitrate directly to the river system. In the absence of mole drains, nitrate loss in surface drainage averaged 6 kg N ha⁻¹, compared with 4 kg N ha⁻¹ in the presence of drains. However, in one year, exceptionally high amounts of nitrate (80 kg N ha⁻¹) were lost from undrained, direct-drilled land because of poor crop establishment; deep leaching of nitrate in the undrained soil was not measured. Approximate calculations show that up to half the autumn-applied fertiliser-N was lost by leaching and up to 15% of spring applications.     

The effects of compost in a rice–wheat cropping system on aggregate size,carbon and nitrogen content of the size–density fraction and chemical composition of soil organic matter,as shown by 13C CP NMR spectroscopy

We investigated whether the long‐term application of compost from agricultural waste improved soil physical structure, fertility and soil organic matter (SOM) storage. In 2006, we began a long‐term field experiment based on a rice–wheat rotation cropping system, having a control without fertilizer (NF) and three treatments: chemical fertilizers (CF), pig manure compost (PMC) and a prilled mixture of PMC and inorganic fertilizers (OICF). Following the harvest of wheat in 2010, the mean‐weight diameter (MWD) of water‐stable aggregates and the concentration of C and N in bulk soil (0–20 cm; <2 mm fraction) were significantly greater (P < 0.05) in PMC and NF plots than in CF or OICF plots. Pig manure compost significantly increased the proportion of >5‐mm aggregates, whereas CF significantly increased the proportion of 0.45‐ to 1‐mm aggregates. The C and N contents of all density fractions were greater in PMC than in other treatments with levels decreasing in the following order: free particulate organic matter (fPOM) >occluded particulate organic matter (oPOM) > mineral‐combined SOM (mineral–SOM). Solid‐state ¹³C CPMAS NMR spectra showed that alkyl C/O‐alkyl C ratios and aromatic component levels of SOM were smaller in PMC and OICF plots than in CF plots, suggesting that SOM in PMC and OICF plots was less degraded than that in CF plots. Nevertheless, yields of wheat in PMC and NF plots were smaller than those in CF and OICF plots, indicating that conditions for producing large grain yields did not maintain soil fertility.     

Evidence for effects of CO2 on soil solution chemistry in spodosols by a simple in-field extractor

Degassing of CO₂ during collection of soil solution may alter the chemical composition of the solution, especially in well-buffered soils. We used a simple syringe extractor for field sampling of soil solution along with ambient soil air in order to test the influence of degassing of CO₂ on solution pH in acid soils (Spodosol B and C horizons collected in Central Maine, USA). Soil air concentrations of CO₂ varied from 0.36 to 1.35 ml l-¹ during sampling immediately after snow melt. Degassing increased solution pH by 0.3 to 0.5 pH units. Both in-situ and degassed pH were predicted by the Reuss and Johnson soil chemical equilibrium model. The results suggest, (i) that the simple method is useful for determination of solution from wet soil under ambient soil air conditions and (ii) that degassing plays a significant role for soil solution chemistry even in Spodosol B and C horizons.     

Evaluation of porous ceramic cups for monitoring soil-water aluminium in acid soils: comment on a paper by Raulund-Rasmussen (1989)

Following recent observations by Raulund-Rasmussen (1989) implicating A1 contamination of soil solutions isolated by suction-cup samplers, A1 release from porous ceramic cups in acid solutions was investigated. In our studies a flush of Al, followed by a gradual decrease in leaching over successive extractions was observed. The amount of Al released was retarded by the presence of 37 μmol dm^?3 of A1 in solution. Gibbsite solubility controls were not observed; all solutions isolated by the cups were undersaturated with respect to amorphous gibbsite. The cups evaluated in this study are appropriate for sampling acidic soil solution, provided they are suitably pretreated and then equilibrated in the field before use.     

Reaction to a paper by Whitaker and Dickens on aflatoxin testing plans for shelled peanuts in the U.S. and the export market

The present paper examines a technical paper of Whitaker and Dickens on aflatoxin testing plans that discusses (without a literature reference) a testing plan used in The Netherlands. However, this testing plan has never been in operation. We present the current situation in The Netherlands with respect to legislation and sampling plans on aflatoxin, which has fairly important consequences for the results of the simulation study of Whitaker and Dickens. It is shown that the percentage of rejected U.S.-exported lots in The Netherlands would increase from 16% to 27% based on the actual testing plan in The Netherlands. The need for international harmonization of testing, and the role of Codex Allmentarius is also emphasized.     

New method for the determination of benzoic and sorbic acids in commercial orange juices based on second-order spectrophotometric data generated by a pH gradient flow injection technique

Two widely employed antimicrobials, benzoic and sorbic acids, were simultaneously determined in commercial orange juices employing a combination of a flow injection system with pH gradient generation, diode array spectrophotometric detection, and chemometric processing of the recorded second-order data. Parallel factor analysis and multivariate curve resolution-alternating least-squares were used for obtaining the spectral profiles of sample components and concentration profiles as a function of pH, including provisions for managing rank-deficient data sets. An appropriately designed calibration with a nine-sample set of binary mixtures of standards, coupled to the use of the second-order advantage offered by the applied chemometric techniques, allowed quantitation of the analytes in synthetic test samples and also in commercial orange juices, even in the presence of unmodeled interferents (with relative prediction errors of 8.7% for benzoic acid and 2.5% for sorbic acid). No prior separation or sample pretreatment steps were required. The comparison of results concerning commercial samples with a laborious reference technique yielded satisfactory statistical indicators (recoveries were 99.0% for benzoic acid and 101.4% for sorbic acid).