Chemical and microbial diagenesis of humic matter in freshwaters

The importance of microbial activity in changing the chemical properties of humic material in brown waters was measured as a function of pH, acid neutralization capacity (ANC), and pK_a affinity spectrum from brownwater samples kept in aquaria and sterile flasks. Changes to the humic matter in non-sterile microcosms caused increases in pH and ANC and loss of strong organic acid pK_a sites. Microbial activity was shown to be the main contributor to a decrease in acidity of humic material as samples kept under sterile conditions showed less change than non-sterile ones. Microbial processes were shown to be mostly due to sessile organisms on the walls of the aquaria and in sediments. Our data suggest that acid-base properties of brownwaters can be modified based on residence times, as well as by temperature in their basins. Assuming similar starting humic materials, microbial degradation may account for the lower acidity measured in lakes and large rivers, compared to headwaters.     

Organic matter and carbohydrate distribution in an orthic humic gleysol

Wet sieving was used to separate an Orthic Humic Gleysol into fractions of seven different particle sizes ranging from < 105 μm to 420. All fractions, including the coarse plant residue and water soluble material, were hydrolysed with H₂SO₄ and analysed for total C and neutral sugar content. Their carbohydrate composition was determined by gas-liquid chromatography of the alditol acetates. The major fraction which consisted of particles < 105 μm was enriched by 30% in both organic matter and carbohydrate content. Although the ratio of carbohydrate to organic matter in the major fraction was the same as in the original soil, it varied considerably in the other fractions. The distribution of monomers among the individual fractions varied in a regular pattern. The relative amount of monomers (hexoses, pentoses and deoxyhexoses) in the major fraction ( < 105 μm, and the water soluble material, were essentially the same as in the original soil. It is concluded that the results of this study support the view that the polysaccharides in soil are of bacterial origin.     

Electrofocusing: A new method for characterization of soil humic matter

Electrofocusing in polyacrylamide gel was carried out on humic substances extracted by 0.1 n NaOH, 0.1m Na₄P₂O₇, and by the method of Burns, El Sayed and McLaren (1972) from the upper and lower organic horizons of an alpine podsol. The electrophoretic patterns were characteristic of both humus origin and extractions procedure. The best resolution of the isoelectric bands for the humus were obtained by the Burns-McLaren procedure. The ionic component does not have much influence on the distribution of humus constituents within the electrophoretic pattern, but the presence of phosphate appears to be essential to obtain good separations.     

不同土壤肥力水平下玉米氮素吸收和利用的研究

盆栽试验条件下利用15N同位素示踪技术研究了不同土壤肥力水平下夏玉米氮肥吸收利用的差异。结果表明:中(M)、低(L)肥力土壤的施肥比对应不施肥空白对照的增产效果要好于高肥力土壤(H)。等NPK用量情况下,高肥力土壤(H-NPK)玉米籽粒产量分别比低肥力(L-NPK)和中肥力(M-NPK)土壤高出23.07%和12.40%。M-NPK处理的玉米籽粒吸收的氮素占总吸氮量的比例最高,达到82.3%。在本试验条件下,玉米吸收的肥料氮与土壤氮比例接近1∶1;L-NPK和M-NPK处理的肥料氮贡献率显著高于H-NPK处理。L-NPK处理玉米的氮肥表观利用率较M-NPK和H-NPK处理分别高出约2个百分点,而同位素15N研究表明,高(H-NPK)、低(L-NPK)肥力土壤之间的氮肥利用率差异不显著,但均较中(M-NPK)肥力土壤高出6.78%和7.65%。L-NPK处理的氮素激发率最高,其次为M-NPK处理,但二者间无显著性差异,且均较H-NPK处理显著高出37.30%和26.98%。     

生物质炭与有机物料配施的土壤培肥效果及对玉米生长的影响

生物质炭作为一种多功能的土壤培肥材料被广泛应用,但其与传统有机物料的对比及配施研究还比较少。通过盆栽试验,研究了生物质炭与秸秆、发酵鸡粪单施及配施对壤质潮土和砂土养分含量、酶活性及玉米生长的影响,并采用主成分分析方法对3种有机物料的培肥效果进行综合评价。试验设6个处理,分别为不添加有机物料(CK)、添加生物质炭(BC)、小麦秸秆(WS)、发酵鸡粪(CM)、秸秆和生物质炭(WS+BC)、鸡粪和生物质炭(CM+BC)。研究结果表明,各处理均增加了砂土玉米生物量和株高,3种有机物料的提升幅度排序为:鸡粪生物质炭秸秆,鸡粪还可增加壤质潮土玉米生物量和株高。添加生物质炭和有机物料还可提高土壤有机质含量,其中生物质炭的提升幅度最大。此外,3种有机物料对土壤养分和酶活性的影响各异,单施鸡粪分别增加壤质潮土和砂土的碱解氮22.08%和26.67%,速效磷91.92%和53.65%,脲酶活性40.54%和36.94%;单施生物质炭分别增加壤质潮土和砂土速效磷83.52%和89.91%,速效钾79.38%和127.02%,过氧化氢酶活性3.41%和11.22%,却降低了土壤碱解氮含量,且与鸡粪配施后会抑制鸡粪中氮的有效性;单施秸秆分别增加壤质潮土和砂土速效钾49.48%和63.02%,β-葡糖苷酶活性51.86%和59.09%;生物质炭与鸡粪或秸秆配施可以更均衡地提升土壤肥力。通过主成分分析和相关分析发现,玉米生物量和株高与土壤氮、磷供应正变化的第2主成分(PC2)得分呈极显著正相关关系。因此,3种有机物料中,鸡粪对土壤氮、磷含量及相关酶活性影响最大;秸秆对土壤钾以及纤维素分解相关酶影响较大,而生物质炭对土壤肥力的提升作用更均衡,且土壤肥力综合得分最高。秸秆或鸡粪配施生物质炭可以更全面地提高土壤肥力。     

Chemical properties of humic matter as related to induction of plant lateral roots

A series of humic matter samples isolated from a soil sequence, different oxisols, size‐fractionated from a vermicompost humic acid and subjected to chemical modifications, were characterized by CPMAS ¹³C‐NMR spectroscopy. The relative signal areas in chemical shift regions of NMR spectra of the four sets of samples were analysed by principal component analysis (PCA). Hierarchical cluster analysis (HCA) was applied to build a classification model, which allowed the recognition of humic matter according to its origin. The relationship between carbon species and biological activity of humic acids, as promoters of lateral root emergence, was obtained by applying PLS multivariate analysis. This showed that lateral root emergence was mostly related to NMR parameters such as the hydrophobicity index (HB/HI) and the 40–110 and 160–200 ppm chemical shift regions (hydrophilic carbon HI), while the content of hydrophobic (HB) carbon in humic samples was negatively correlated with induction of lateral root hair. Our results represent a step further in the structure‐bioactivity relationship of natural humic substances and confirm their role as plant root growth promoters.     

Interpretation of humic acid coagulation and soluble soil organic matter using a calculated electrostatic potential

The coagulation of humic substances and its role in controlling the solubility of organic matter in soils are not well understood. We therefore studied the physico‐chemical behaviour of purified humic acid from forest soil coagulated with Na, Ca, Cu, Al at pH 4 and 6, and then modelled the behaviour with the Non‐Ideal Consistent Competitive Adsorption Donnan (NICA‐Donnan) model. We found that the coagulation of humic acid occurs when the Donnan potential is less negative than ?0.08 V. Based on this result, an empirical relation between the Donnan potential of humic acid and its concentration in solution was derived. In addition, the Donnan potential of the dissolved organic matter in the soil solution of six soil profiles from forests was calculated using the NICA‐Donnan model under the assumption that all the dissolved organic matter behaves as humic acid. The measured concentration of dissolved organic matter also decreases in a soil profile, as the calculated potential becomes less negative. The results are in many cases in semi‐quantitative agreement with the predicted concentration based on the humic acid coagulation experiment. Acid soils contain more dissolved organic matter, which may result from the presence of a fairly large fraction of more soluble organic molecules, such as fulvic acid.     

Organic matter retention in an upland humic podzol; the effects of pH and solute type

This paper discusses the effects of different horizons and soil solution compositions on dissolved organic matter retention in a moorland podzol and compares the results with previous studies of forest podzols. Adsorption isotherms were constructed for each of the major horizons of a freely draining, upland, moorland, humic podzol from north-east Scotland, to investigate processes of retention and release of dissolved organic matter (DOM). Carbon retention of a range of solute types was studied, and phthalate was chosen as a model compound to measure carbon retention at three different pH values (3, 4.5 and 6). Retention and release of DOM was related to chemical, physical and mineralogical characteristics of the different soil horizons. All the mineral horizons retained DOM, with the Bs horizon most retentive. Solution pH did not significantly affect DOM retention in the O and A horizons. At pH 3 and 4.5 organic matter was weakly retained in the Bhs horizon, but strongly retained in the Bs and the Cx horizons. At pH 6 reversal of surface charge occurred in the Bs and Cx horizons resulting in the release of similar amounts of organic matter to that released from the O horizon at the same pH. The results demonstrate how podzols act as a ‘valve’ in controlling the input of dissolved organic compounds into surface and ground water, and how sensitive the controlling mechanisms are to pH change.     

Effects of land-use and management practices on soil ergosterol content in andosols

Ergosterol is a fungus-specific chemical component which has been extensively used to assess the fungal biomass and activity in soils. In the present study, we investigated the soil ergosterol content in a group of Japanese soils differing in management. In addition, the relationships among the soil ergosterol content (SEC), microbial biomass C (MBC), and microbial biomass N (MBN) were also tested in different seasons. Our results showed that the SEC was lower in intensively cropped soils than in pasture and forest soils. In general, no consistent trend was observed for SEC of pasture soils within the same sampling period. However, SEC tended to decrease in most of the soils in autumn, which may be ascribed to the effect of seasonal changes on fungal biomass. No strong evidence could be obtained for the effect of different fertilizers on SEC, which can be due to different management variables and interspecific variations between fungal communities at different soil sites. Our results did not suggest the presence of a noticeable correlation between SEC and MBC or MBN. The ratio of SEC in total biomass C was lower (0.20 and 0.11% in spring and autumn, respectively) compared with the values reported.     

Relationships between the primary mineral and the clay mineral compositions of some recent andosols

Relationships between the clay mineralogy and the primary mineral association were studied on seventeen Andosol samples (<3,000 years old) collected from Aomori, Hokkaido, and Iwate. Opaline silica, allophane, and imogolite were predominant in the soils derived from volcanic ashes which contained practically no quartz, while opaline silica, crystalline layer silicates, alumina-rich gel-like materials, and allophanelike constituents were abundant in the soils which contained abundant quartz. There was no positive indication of the presence of allophane in any quartz andesitic Andosols. High contents of finely comminuted amphibole and mica in the quartz andesitic volcanic ashes suggested that the crystalline layer silicates are inherited and are not formed pedochemically from amorphous materials.     

Studies on the properties of organic matter in buried humic horizon derived from volcanic ash

Abstract

Humic acids were extracted from the surface horizon Yu 1 and buried humic horizons (Yu 2, 800-864 AD; Yu 4, ca. 4,000 years B.P.; Yu 6, 7,000 years B.P.; Yu 7, ca. 10,000 years B.P.). The humic acids were filtered with ultramembranes with 20, 10, 5, 1 or 0.1 × 10' M.W. in this order and separated into five fractions; (>20), (20-10), (10-5), (5-1) and (1-0.1) × 10⁴ M.W. fractions. The elementary composition, functional groups, optical properties, and hydrolyzable total- and sugar-carbon contents of each humic acid fraction were determined, and the changes in properties of the humic acid with age after burial were discussed.

In horizons Yu 1 to Yu 6, the patterns of M.W. distribution of the >20 × 10⁴ to (1- 0.1) × 10⁴ fractions were rather similar. In contrast, Yu 7 was characterized by the predominance of (1-0.1) x 10' M.W. fraction and the presence of a small amount of <0.1 × 10⁴ M.W. fraction.

The chemical properties of humic acid (HA) fractions of each humic horizon and their changes with age after burial were as folIows:

1) Elementary composition of HA fractions of each humic horizon was rather similar to each other. The C% and C/N ratio increased, and the H%, N% and H/C ratio decreased in all HA fractions with age.

2) Total acidity and carboxyl contents of HA fractions of Yu 1 were higher in the lower M.W. fractions. These values increased with age up to Yu 4 or Yu 6 horizons, then decreased in the Yu 6 or Yu 7 horizon. The contents of carbonyl groups in all the HA fractions which were very low in Yu 1, showed a wide range of variations in Yu 2, intermediate values from Yu 4 to Yu 6 horizons then decreased in the HA fractions of Yu 7, except for the (>20) fraction.

3) The degree of humification of the HA fractions of Yu 1 judging from the RF and \sDlogK values, tended to be higher in higher M.W. fractions, and increased in all the HA fractions with age after burial.

4) Hydrolyzable total- and sugar-carbon contents were high in the HA fractions of Yu 1 and decreased with age.

5) Changes of elementary composition, degree of humification and hydrolyzable total- and sugar-carbon contents were conspicuous from the Yu 1 to Yu 2 horizons, and less significant afterwards.

6) The 0%, C/O ratio and phenolic OH content did not show any consistent change with age after burial.     

Studies on the properties of organic matter in buried humic horizon derived from volcanic ash

To investigate the relationship between age and the sugar composition in hydrolysates of the surface horizon and buried humic horizons with age up to 28,000 years B.P., the neutral sugars and amino sugars in soil hydrolysates were determined.

The ratios of total sugar carbon content to total carbon content of soil ranged from 2.68 to 4.13 percent. These values showed no distinct relationship with age.

Rhamnose, fucose, arabinose, xylose, mannose, galactose, glucose, g1ucosamine and galactosamine were present in the hydrolysates of all soil samples.

The polysaccharides of soil samples which have been buried for shorter periods were dominated by glucose, while those of soil samples buried for longer periods were dominated by mannose.

The proportion of hexoses showed a tendency to increase with age, while that of pentoses showed a tendency to decrease with age.     

Contribution of denitrification and autotrophic and heterotrophic nitrification to nitrous oxide production in andosols

To quantify the contribution of denitrification and autotrophic and heterotrophic nitrification to N₂O production in Andosols with a relatively high organic matter content, we first examined the effect of C₂H₂ concentrations on N₂O production and on changes in mineral N contents. The optimum C₂H₂ concentration for inhibiting autotrophic nitrification was 10 Pa. Secondly, and Andosol taken from an arable field was incubated for 32 days at 30°C at 60, 80, and 100% water-holding capacity with or without the addition of NH ₄ ⁺ or NO _inf3 ^sup- (200 mg N kg^-1), and subsamples collected every 4–8 days were further incubated for 24 h with or without C₂H₂ (10 Pa). At 60 and 80% water-holding capacity with NH ₄ ⁺ added, 87–92% of N₂O produced (200–250 g N₂O–N kg^-1) was derived from autotrophic nitrification. In contrast, at 100% water-holding capacity with or without added NO _inf3 ^sup- , enormous amounts of N₂O (29–90 mg N₂O–N kg^-1) were produced rapidly, mostly by denitrification (96–98% of total production). Thirdly, to examine N₂O production by heterotrophic nitrification, the Andosol was amended with peptone or NH ₄ ⁺ (both 1000 mg N kg^-1)+citric acid (20 g C kg^-1) and with or without dicyandiamide (200 mg N kg^-1). Treatment with citric acid alone or with citric acid+dicyandiamide suppressed N₂O production. In contrast, peptone increased N₂O production (5.66 mg N₂O–N kg^-1) mainly by denitrification (80% of total production). However, dicyandiamide reduced N₂O production to 1.1 mg N₂O–N kg^-1. These results indicate that autotrophic nitrification was the main process for N₂O production except at 100% water-holding capacity where denitrification became dominant and that heterotrophic nitrification had a lesser importance in the soils examine.Dedicated to Professor J. C. G. Ottow on the occasion of his 60th birthday     

Mechanism of reduction of exchangeable aluminum by gypsum application in acid andosols

Mechanism of reduction of exchangeable aluminum in acid Andosols treated with gypsum was studied by using cation exchange resin methods to determine the amount of polymerized aluminum. Two types of acid Andosols were used as test soils: Kitakami light colored Andosol (fine, mixed, mesic, Andic Dystrochrept) and Kawatabi thick high humic Andosol (medial, mesic mixed Alic Pachic Melanudand). Polymerization of aluminum in the soil solution of both Kitakami and Kawatabi Andosols treated with gypsum was suggested based on an analysis using cation exchange resin methods, whereas that in monomer aluminum solution was not detected. Accumulation of polymerized aluminum in both Kitakami and Kawatabi Andosols was determined by using cation exchange resin, and the amounts of polymer aluminum trapped by the resin and the ratio of polymer aluminum to monomer aluminum were increased with the incubation time. The values of CEC which decreased in the Kitakami Andosol after gypsum treatment were almost equivalent to the amounts of cation exchange sites occupied by polymer aluminum ions which were calculated based on the decrease of the values of Y _l. We conclude that the mechanism of reduction of exchangeable aluminum in strongly acid Andosols treated with gypsum is as follows: firstly, exchangeable aluminum adsorbed on the cation exchange sites of soils may be released into the soil solution due to the increase in the ion strength caused by gypsum application, and then monomer aluminum in soil solution may be polymerized in the presence of soil colloidal materials. Consequently, the polymer aluminum formed in the soil solution may be selectively and irreversibly fixed on the cation exchange sites of 2 : 1 clay minerals.     

Combined effects of technical grade fenitrothion, humic acids and particulate matter on cholinesterase activity in freshwater invertebrates

Purpose

The relative sensitivity of two freshwater invertebrate organisms to the organophosphorus insecticide fenitrothion was assessed by measuring cholinesterase (ChE) activity, a well-known biomarker of both exposure and effect to organophosphorus pesticides. The influence of different concentrations of humic acids (HAs) and particulate matter on fenitrothion bioavailability was assessed in the more sensitive species.

Materials and methods

The selected invertebrates were the dwelling feeding oligochaete Lumbriculus variegatus and the pulmonate gastropod Biomphalaria glabrata. Acute 48-h bioassays were performed exposing organisms to different fenitrothion concentrations. The concentrations that induced 50 % inhibition of enzyme activity (EC₅₀) were calculated. Fenitrothion bioavailability was investigated using different concentrations of commercial HA or particulate matter. Sand and a diverse selection of chromatographic resins that have been proposed as analogues of natural sediments were selected. For these experiments, animals were exposed to a fenitrothion value similar to the EC₅₀.

Results and discussion

The 48-h EC₅₀ values were 12?±?2 and 23?±?3 μg?l^?1 for L. variegatus and B. glabrata, respectively. Depending on HA concentration and the characteristics of particles, ChE activity was similar or higher than the value recorded for animals exposed only to the pesticide in aqueous solution.

Conclusion

The results indicated that L. variegatus was the more sensitive species of the two. In this species, fenitrothion bioavailability did not increase due to the presence of either different HA concentrations or particulate matter. The experimental approach may constitute a useful tool to predict the influence of dissolved organic matter and sediment particles on fenitrothion bioavailability and toxicity to non-target aquatic invertebrates.     

Effects of pH, ionic strength, and solutes on DNA adsorption by andosols

The adsorption of DNA by two andosols was investigated as function of solution pH, ionic strength in solution and some solutes, so as to understand the behavior of extracellular DNA molecules in two andosols. DNA adsorptions greatly decreased by increasing pH of suspensions in a pH range of 3.0–9.0. The adsorption of DNA molecules by both andosols was not affected by ionic strength from 0.1 to 0.5 mol L⁻¹ NaCl. However, the DNA adsorption increased proportionally by increasing Mg²⁺ concentration in the suspension. Addition of phosphate decreased DNA adsorption, indicating competition between DNA molecules and phosphate ion in the adsorption by andosols. These results suggest that there are several DNA adsorption mechanisms in soil.     

外源胡敏酸对土壤有机质组分变化的影响及其与茶树铅有效性的关系

盆栽试验分析了胡敏酸输入土壤6个月后茶树根际和非根际土壤有机质SOM及其组分,包括水溶性物质WSS、富啡酸FA、胡敏酸HA以及土壤微生物生物量SMB的变化,并对不同土壤有机质组分碳含量和茶树不同组织铅含量作了相关性分析。外源胡敏酸设置3个浓度水平（0、300、600 mg kg-1）,铅设置2个浓度水平（0、300 mg kg-1）,试验共有6个处理。茶苗置于温室培养,6个月后分新叶、老叶、新茎、老茎、根收获。结果表明：根际并非总是富含有机质,未加铅处理根际SOM含量低于非根际;而加铅处理根际SOM含量高于非根际。HA加入土壤能够显著增加根际和非根际SOM和SMB的含量,但是加铅处理和不加铅处理增加幅度不同。高浓度HA显著增加了根际FA的含量,可能是HA部分裂解所致。非根际有机质各组分与茶树铅含量无显著相关关系;根际SOM、HA和茶树不同组织铅含量没有显著相关关系。根际WSS、FA与茶树嫩叶、老叶、嫩茎、老茎以及根部铅含量均存在显著或极显著正相关关系;而根际SMB与茶树各个组织铅含量存在显著负相关关系。总之,胡敏酸施入土壤改变了土壤有机质及其各个组分的含量,而根际某些土壤有机质组分的改变又显著影响了茶树不同组织铅的吸收和分布。     

Nitrogen mineralization in soil layers, soil particles and macro-organic matter under grassland

 A study was conducted to determine mineralization rates in the field and in different soil layers under three grassland managements (viz. a reseeded sward, a permanent sward with a conventional N management, and a long-term grass sward with 0 N (0-N) input). Potential mineralization rates of soil particles (sand, silt and clay) and macro-organic matter fractions of different sizes (i.e. 0.2–0.5, 0.5–2.0 and >2 mm) were also determined in the laboratory. In the reseeded plots, net mineralization was unchanged down to 40 cm depth. In the undisturbed conventional-N swards, mineralization rates were substantially higher in the top layer (0–10 cm) than in the deeper layers. In plots which had received no fertilizer N, mineralization was consistently low in all the layers. There was more macro-organic matter (MOM) in the 0-N plots (equivalent to 23 g kg^–1 soil for 0–40 cm) than in the two fertilized plots (i.e. conventional-N and reseeded) which contained similar amounts (ca. 15 g kg^–1 soil). C and N contents of separated soil particles did not differ amongst the treatments, but there were large differences with depth. Potential mineralization in the bulk soil was greatest in the 0–10 cm layers and gradually decreased with depth in all the treatments. Separated sand particles had negligible rates of potential mineralization and the clay component had the highest rates in the subsurface layers (10–40 cm). MOMs had high potential rate of mineralization in the surface layer and decreased with soil depth, but there was no clear pattern in the differences between different size fractions. Received: 17 November 1997