Digestion of microbial biomass, structural polysaccharides, and protein by the humivorous larva of Pachnoda ephippiata (Coleoptera: Scarabaeidae)

In order to investigate whether microbial biomass and its residues are nutrient and energy sources for humivorous beetle larvae, we carried out feeding trials using soil supplemented with ¹⁴C-labeled fungal biomass (Penicillium chrysogenum), bacterial biomass (Bacillus megaterium), fungal or bacterial structural polysaccharide (chitin, peptidoglycan), bacterial protein, or cellulose, taking the larva of the cetoniid beetle Pachnoda ephippiata (Coleoptera: Scarabaeidae) as a model of a humus-feeding beetle larva with a highly alkaline gut. The results showed that gut passage strongly stimulated the mineralization of the structural polymers. The stimulatory effect correlated positively with the recalcitrance of the preparation in the control soil, and was accompanied by a transformation of the residual radiolabel to alkali-soluble and acid-soluble products. The solubility increase was highest in the extremely alkaline midgut. High-performance gel-permeation chromatography demonstrated that the changes in solubility were accompanied by reciprocal changes in the molecular weight of the residual material and that the residual material in the fecal pellets was more humified than in the control soil. The amount of radiolabel recovered from the body and hemolymph of the larvae indicated that microbial biomass and its structural components were assimilated more efficiently than cellulose, which supports the hypothesis that microorganisms and the nitrogenous components of humus are an important dietary resource for humivorous soil macroinvertebrates.     

Selective digestion of the proteinaceous component of humic substances by the geophagous earthworms Metaphire guillelmi and Amynthas corrugatus

Humic substances play a key role in the global carbon cycling and the sequestration of micropollutants in soil. The transformation of these substances by earthworms, the dominant soil macroinvertebrates of many terrestrial ecosystems, and the mechanisms involved are still obscure. We prepared two chemically identical humic model compounds that were specifically ¹⁴C-labeled either in the aromatic or the proteinaceous component, and added them to soil incubated with the geophagous earthworm species Metaphire guillelmi (anecic) and Amynthas corrugatus (endogeic). In the absence of the earthworms, both the aromatic and the proteinaceous components were mineralized at similarly low rates (5−8% after 9 days of incubation). In the presence of the earthworms, mineralization rate of the proteinaceous component was strongly stimulated (2-fold by M. guillelmi and 1.4-fold by A. corrugatus). The mineralization rate of the aromatic component was (slightly) stimulated (1.2-fold; P < 0.05) only by A. corrugatus. In all cases, the stimulated mineralization was accompanied by a transformation of radiolabeled humic acids to fulvic acids within the earthworm guts and by an incorporation of radiolabel into the earthworm tissues. Digestion of the proteinaceous component of humic acids by the earthworms was corroborated also by a decrease of extractable humic acids in fresh cast and a stimulated mineralization of soil nitrogen; in the case of M. guillelmi, the fresh cast contained sixfold more NH₄⁺ than the non-ingested soil. Our study provides direct evidence for the selective digestion of humic components by earthworms. Considering the ubiquity of geophagous earthworms and their large biomass, the alteration of the chemical structure of humic substances by the earthworms through their selective digestion of peptidic components may have significant impacts on the stability of humic substances and the bioavailability of micropollutants in soil.     

Digestion and residue stabilization of bacterial and fungal cells,protein, peptidoglycan,and chitin by the geophagous earthworm Metaphire guillelmi

Microbial biomass is an important source of soil organic matter, which plays crucial roles in the maintenance of soil fertility and food security. However, the mineralization and transformation of microbial biomass by the dominant soil macrofauna earthworms are still unclear. We performed feeding trials with the geophagous earthworm Metaphire guillelmi using ¹⁴C-labelled bacteria (Escherichia coli and Bacillus megaterium) cells, fungal (Penicillium chrysogenum) cells, protein, peptidoglycan, and chitin. The mineralization rate of the microbial cells and cell components was significantly 1.2–4.0-fold higher in soil with the presence of M. guillelmi for seven days than in earthworm-free soil and 1–11-fold higher than in fresh earthworm cast material. When the earthworms were removed from the soil, the mineralization of the residual carbon of the microbial biomass was significantly lower than that in the earthworm-free soil, indicating that M. guillelmi affects the mineralization of the biomass in soil in two aspects: first stimulation and then reduction, which were attributed to the passage of the microbial biomass through the earthworm gut, and that the microorganisms in the cast could play only minor roles in the stimulated mineralization and residual stabilization of microbial biomass. Large amounts (8–29%) of radiolabel of the tested microbial biomass were assimilated in the earthworm tissue. Accumulation of fungal cells (11%) and cell wall component chitin (29%) in the tissue was significantly higher than that of bacterial cells (8%) and cell wall component peptidoglycan (15%). Feeding trails with ¹⁴C-lablled microbial cells and cell components provided direct evidence that microbial biomass is a food source for geophagous earthworm and fungal biomass is likely a more important food source for earthworms than bacterial biomass. Findings of this study have important implications for the roles of geophagous earthworms in the fate of microbial biomass in soil.     

Transformation and mineralization of 14C-labeled cellulose, peptidoglycan, and protein by the soil-feeding termite Cubitermes orthognathus

 We performed feeding trials with the soil-feeding termite Cubitermes orthognathus using soil spiked by uniformly ¹⁴C-labeled preparations of cellulose, peptidoglycan, protein, and bacterial cells (Bacillus megaterium and Escherichia coli). When incubated in soil for 8 days in the absence of termites, cellulose and peptidoglycan showed low mineralization rates (0.5% and 0.2%, respectively). However, when termites were present, their mineralization rates strongly increased (21.6% and 30.6%, respectively). The mineralization rate of protein was 12.4% in the control soils and increased to 36.2% in the presence of termites. Mineralization of bacterial cells in control soils occurred in two phases (rapid mineralization during the first 4–5 days and stabilization thereafter). When termites were present, the rates of mineralization of bacterial cells increased and the stabilization phase was abolished. In all cases, radiolabel accumulated in the termites and the solubility of the labeled compounds located in the gut increased strongly. Mineralization was accompanied by transformation of residual carbon from the humic acid fraction to the fulvic acid fraction during gut passage. High-performance gel permeation chromatography demonstrated a strong shift in the size distribution of the residual carbon from high-molecular-weight towards low-molecular-weight molecules in the gut of termites and an accumulation of small molecules in the termite bodies. The present study provides strong evidence that structural polysaccharides of plants and bacteria and microbial biomass are carbon and energy sources for soil-feeding termites. Received: 29 May 2000     

Decomposition and distribution of residual activity of some 13C-microbial polysaccharides and cells,glucose, cellulose and wheat straw in soil

Studies were made to determine the rate of decomposition of some ¹⁴C-labeled microbial polysaccharides, microbial cells, glucose, cellulose and wheat straw in soil, the distribution of the residual ¹⁴C in various humic fractions and the influence of the microbial products on the decomposition of plant residues in soil. During 16 weeks from 32 to 86 per cent of the C of added bacterial polysaccharides had evolved as ¹⁴CO₂. Chromobacterium violaceum polysaccharide was most resistant and Leuconostoc dextranicus polysaccharide least resistant. In general the polysaccharides, microbial cells, and glucose exerted little effect on the decomposition of the plant products. Upon incubation the ¹⁴C-activity was quickly distributed in the humic. fulvic and extracted soil fractions. The pattern of distribution depended upon the amendment and the degree of decomposition. The distribution was most uniform in the highly decomposed amendments. After 16 weeks the bulk of the residual activity from Azotobacter indicus polysaccharide remained in the NaOH extracted soil. From C. violaceum polysaccharide both the extracted soil and the humic acid fraction contained high activity. About 50–80 per cent of the residual activity from the ¹⁴C-glucose, cellulose and wheat straw amended soils could be removed by hydrolysis with 6 n HCl. The greater part of this activity in the humic acid fraction was associated with the amino acids and that from the fulvic acids and residual soils after NaOH extraction with the carbohydrates. About 8 16 per cent of the activity of the humic acid fraction was present in substances (probably aromatic) extracted by ether after reductive or oxidative degradation.     

Changes in the content and composition of humus in the sandy loamy soddy-podzolic soil in a long-term liming experiment

The effect of liming on organic matter in sandy loamy soddy-podzolic soil was studied. The study was performed on samples taken from the 50-year-long experiment established by Prof. Kornilov in 1957. It was shown that liming had almost no effect on the total humus content in the soil. The humus composition was studied using two fractionation methods of the humus substances by the Ponomareva-Plotnikova procedure. The regrouping of the humus fractions occurred due to the changes in the mobility of soil mineral components, which involved a regular increase in the content of the Ca-bound fraction of humic acids (HA-2) at the expense of the HA-1 fraction bound to the mobile forms of R₂O₃ reliable at the lime rates equivalent to the total acidity and higher. The levels of the stabilization of the different HA fractions were considered, as well as the stability of the changes in the humus composition during 50 years.     

Influence of intimate association with humic polymers on biodegradation of [C]labeled organic substrates in soil

A variety of [¹⁴C]labeled organic compounds and microbial products were incubated in soil alone or intimately associated with humic acid-type polymers achieved by freeze-drying mixed solutions of the polymers and [¹⁴C]labeled compounds at pH 6. The association of Chlorella protein with the polymers reduced mineralization over 12 weeks by 41%. Similarly decomposition of cysteine and Anabaena flos-aqua cytoplasm was reduced by 26% and glycine 16%. Tyrosine, lysine, aspartic acid, serine, cytosine, glucose, ferulic acid. also polysaccharides of Leuconostoc dextranicus, Azotobacter indicus, Hansenula holstii and Anabaena flos-aqua, as well as cells and cell walls of A. flos-aqua decomposed just or almost as readily when intimately associated with humic polymers as when added alone to the soils. The association with humic polymers did not influence the distribution of residual activity in humic acid, fulvic acid and extracted soil following incubation.     

Further investigations on the chemistry of fungal “humic acids”

In view of the considerable interest in laboratory-prepared fungal “humic acids” as possible precursors or incorporated structural components of soil humic substances, we degraded four fungal “humic acids” by the relatively mild alkaline cupric oxide oxidation. The oxidation products were extracted into organic solvents, methylated, separated by thin-layer chromatography and identified on a gas chromatographic-mass spectrometric-computer system.Average yields of major degradation products were: (a) aliphatic compounds, 38 per cent; (b) benzene-carboxylic compounds, 25 per cent; and (c) phenolic compounds, 21 per cent. The remaining 16 per cent consisted of a number of dialkyl phthalates. Our data agree with those that we reported earlier when we degraded a number of fungal “humic acids” by the more drastic alkaline permanganate oxidation and show that fungal “humic acids” are enormously complex organic materials containing aliphatic and aromatic structures, (some of which contain N), but only a relatively small proportion of which is phenolic. Most of the aliphatics isolated consisted of alkanes and fatty acids, which are known to persist in soils over long periods of time and are frequently firmly retained by soil humic substances.     

A comparative study on the chemical composition of humic acids from forest soil,agricultural soil and lignite deposit: Bound lipid,carbohydrate and amino acid distributions

Base- and acid-hydrolysable fractions of humic acids (HAs) isolated from a forest soil, an agricultural soil and a lignite deposit were analysed, and comparisons were made between the base hydrolysable lipid (bound lipid), carbohydrate and amino acid signatures of the different humic acids.Bound lipids differ depending on the humic acid origin. Their composition were rather similar for the two soil humic acids, with three main lipid classes identified: (i) aliphatic components, (ii) aromatic components and (iii) sterols and triterpenols. The aliphatic subfraction was the most abundant and consisted predominantly of cutin- and suberin-derived moieties some of which could be clearly related to the vegetation. A minor bacterial input was indicated by the presence of short chain α- and β-hydroxyalkanoic acids. Aromatic subfraction contributed to a low amount to the total base hydrolysates and consisted mainly of lignin-derived methoxyphenols. Present in trace amounts, sterols and triterpenols are mainly of higher plant origin. The base hydrolysate from lignite humic acid markedly differs. Bound lipids released from lignite HA comprised almost exclusively aliphatic components, largely dominated by long chain alkanoic acids. Lignin-derived moieties, hardly detected, consisted solely of vanillic and 4-hydroxybenzoic acids indicating a much higher degree of lignin alteration in lignite humic acid. Sterols and triterpenols were absent.Although the composition of monosaccharides released upon acid hydrolysis was rather uniform irrespective of the humic acid origin, the distribution changed with the degree of humification of the HAs. Ratios of (Galactose+Mannose) to (Xylose+Arabinose) increased from soil to lignite humic acids. The high values of the ratios indicate that carbohydrates are primarily of microbial origin.In all humic acids neutral and acidic protein amino acids dominated. Non protein amino acids were only minor components consisting mainly of hydroxy proline and ornithine. The amino acid distributions of both soil HAs were similar. The amino acid distribution of lignite HA resembled that of soil HAs except for the following differences: (1) the absence of hydroxy proline and the greater abundance of ornithine suggesting a higher microbial contribution to the amino acids as the degree of humification increases, (2) the higher contribution of polar amino acids suggesting a preferential preservation of these amino acids possibly by interaction with the humic acid surface through hydrogen bonds.     

Sequential exhaustive extraction of a Mollisol soil, and characterizations of humic components, including humin, by solid and solution state NMR

A comprehensive sequential extraction procedure was applied to isolate soil organic components using aqueous solvents at different pH values, base plus urea (base‐urea), and finally dimethylsulfoxide (DMSO) plus concentrated H₂SO₄ (DMSO‐acid) for the humin‐enriched clay separates. The extracts from base‐urea and DMSO‐acid would be regarded as ‘humin’ in the classical definitions. The fractions isolated from aqueous base, base‐urea and DMSO‐acid were characterized by solid and solution state NMR spectroscopy. The base‐urea solvent system isolated ca. 10% (by mass) additional humic substances. The combined base‐urea and DMSO‐acid solvents isolated ca. 93% of total organic carbon from the humin‐enriched fine clay fraction (<2 μm). Characterization of the humic fractions by solid‐state NMR spectroscopy showed that oxidized char materials were concentrated in humic acids isolated at pH 7, and in the base‐urea extract. Lignin‐derived materials were in considerable abundance in the humic acids isolated at pH 12.6. Only very small amounts of char‐derived structures were contained in the fulvic acids and fulvic acids‐like material isolated from the base‐urea solvent. After extraction with base‐urea, the 0.5 m NaOH extract from the humin‐enriched clay was predominantly composed of aliphatic hydrocarbon groups, and with lesser amounts of aromatic carbon (probably including some char material), and carbohydrates and peptides. From the combination of solid and solution‐state NMR spectroscopy, it is clear that the major components of humin materials, from the DMSO‐acid solvent, after the exhaustive extraction sequence, were composed of microbial and plant derived components, mainly long‐chain aliphatic species (including fatty acids/ester, waxes, lipids and cuticular material), carbohydrate, peptides/proteins, lignin derivatives, lipoprotein and peptidoglycan (major structural components in bacteria cell walls). Black carbon or char materials were enriched in humic acids isolated at pH 7 and humic acids‐like material isolated in the base‐urea medium, indicating that urea can liberate char‐derived material hydrogen bonded or trapped within the humin matrix.     

Transformation of the organic matter in an agrogray soil and an agrochernozem in the course of the humification of corn biomass

The transformation of the organic matter in the course of corn residues humification in an agrogray soil and an agrochernozem was studied in long-term experiments using the method of solid-phase ¹³C-nuclear magnetic resonance spectroscopy. The humification of the plant residues was found to be accompanied by a decrease in the content of the O-alkyl fragments comprising polysaccharides and polypeptides, an increase in the unsubstituted alkyds content, and by the relative accumulation of aromatic fragments and carboxyl groups. The most strongly transformed pool of the organic matter, as compared to the initial plant residues, was the humic acids with their maximal content of aromatic and carboxyl functional groups and the minimal content of O-alkyls. The chemically stable aromatic fragments were concentrated not only in the pool of humic acids; their content was 64–89% of the pool of the aromatic fragments identified in the soil organic matter. Therefore, to assess the stable pool, the distribution of the functional groups is necessary to be analyzed not only in the humic acids but also in the whole soil organic matter.     

Sodium amalgam reduction of humic acid—II. application of the method

The nature and distribution of the phenolic compounds found in humic acid on sodium amalgam reduction resemble those reported to be found in microbial cultures grown on lignifiedplanttissue.lt has also been shown that the more humified and decayed fractions of soil organic matter yield humic acids that bear less resemblance to lignin than do the humic acids from less decayed plant remains. The aromatic portion of humic acid would seem to consist of biologically modified and transformed lignin, together with phenolic units synthesized by soil microbes. Sodium amalgam reduction can be employed to estimate the degree of transformation, but cannot, however, be used to “finger print” humic acids.     

Wechselwirkungen zwischen Boden-Huminstoffen und Metall-Ionen I. Isolierung und Charakterisierung der Boden-Huminstoffe

Interactions between soil humic substances and metal ions I. Isolation and characterization of the soil humic substances From two horizons of a podzol humic acids and fulvic acids were isolated by two different methods. The obtained samples were characterized by elemental analysis, the determination of the ash and moisture content, functional group analysis as well as FTIR-, ¹H-NMR-, and ¹³C-NMR-spectroscopic examinations. In spite of the different isolation methods humic and fulvic acids show great similarities. A higher oxidized state and a lower content of aromatic structural features are clearly observed in the fulvic acids in contrast to humic acids. Besides aromatic structural elements, distinct aliphatic sections were detected in the investigated samples, which showed a lower concentration in the less transformed fractions of the Ahe-horizon.     

The effect of long-term fertilizer application on the group and fractional composition of humus in a soddy-podzolic light loamy soil

The effect of lime and organic and mineral fertilizers on the fractional and group composition of the humus in a light loamy soddy-podzolic soil was studied in a long-term experiment. The application of lime increased the content of the agronomically valuable fraction of humic acids (HA-2) by 2.6 times on the average. The application of mineral fertilizers at the rate of N83P61K112 (kg/ha per year) increased the mobility of the humic substances; the application of farmyard manure (12.5 t/ha per) has an opposite effect. In general, various fertilizer systems exerted a favorable effect on the qualitative composition of the humus with an increase in the percentage of humic acids, though the humate-fulvate type of humus was preserved in all the variants of the experiment.     

改良剂施用对矿区复垦土壤水稳性团聚体及有机碳组分的影响

  目的  探究施用不同种类和数量改良剂对矿区复垦土壤水稳性团聚体和有机碳的影响。  方法  在山西省古交市屯兰煤矿复垦6年的地块上设置随机区组试验,在0 ~ 20 cm土层按土壤重量的1%、3%、5%分别施用腐殖酸和泥炭两种改良剂,于施用后1年和2年时两次取样测定0 ~ 20 cm土壤团聚体组成、有机碳含量及其组分,对不同种类和数量改良剂的改良效果进行评价。  结果  施用腐殖酸、泥炭后1年时各处理土壤 > 2 mm水稳性团聚体质量分数均高于对照,增幅为1.53% ~ 62.27%,且土壤水稳性团聚体均以大团聚体（> 0.25 mm）为主;施用改良剂后2年时各处理土壤水稳性大团聚体含量降低,降幅为1.73% ~ 11.35%,土壤团聚体以 < 0.053 mm粒级的团聚体为主。施用改良剂后腐殖酸处理的土壤有机碳储量、固碳量和固碳速率呈先增加后减少的趋势,泥炭处理随泥炭施用量的增加而增加。施用改良剂后土壤 > 2 mm粒级团聚体质量分数与土壤有机碳储量呈显著正相关。施用改良剂能增加复垦土壤矿物结合态有机碳含量,且施用腐殖酸处理的含量高于泥炭处理。施用改良剂后2年时与1年相比,复垦土壤颗粒态有机碳含量呈增长的趋势,土壤铁铝键结合态有机碳含量则呈降低趋势。施用腐殖酸、泥炭可增加复垦土壤羧酸、醇类等官能团含量,显著增加土壤中多糖物质的含量。  结论  在矿区复垦土壤上施用腐殖酸、泥炭可显著增加土壤大团聚体数量,提高土壤有机碳、矿物结合态有机碳和颗粒态有机碳含量及土壤固碳量;随腐殖酸、泥炭施用量增加,土壤固碳速率增加、固碳效率减小;复垦区土壤改良需逐年施用腐殖酸、泥炭等改良剂,才能获得稳定的改良效果。     

Chitin decomposition in a model soil system

The effect of various organisms on the decompositon of chitin in a gnotobiotic soil system was investigated. Chitin decomposers were isolated from the short grass prairie in Colorado and selected by their ability to use chitin as a source of both C and N. Three bacteria, a fungus, and an actinomycete were grown for 45 days in sterile chitin amended (3 mg g^?1 chitin-C) and unamended soil microcosms. Net mineralization of ammonium was greatest in the chitin-ainended microcosms. The greatest increases in N mineralization occurred in chitin-amended microcosms containing the fungus and the actinomycete. A second series of sterile soil microcosms amended with chitin (3 mg g^?1 chitin-C) were inoculated with decomposers, a fungus and a bacterium, and a nematode and an amoeba (bacteriophagic grazers) in various combinations. Bacterial and grazer populations, NH₄⁺ CO₂ evolution, and residual chitin were measured periodically for 80 days. Bacterial grazing reduced bacterial populations, increased N mineralization, but had no effect on the decomposition of chitin.     

A model for a type humic acid

In the preceding papers (1,2,3,4), the author studied some chemical properties of soil humic acids, and compared various so-called artificial humic acids with soil humic acids in respect to their absorption spectra and stabilities. According to these experimental results, it is Presumed that soil humic acids, especially A type, must contain not only benzene ring, but also condensed aromatic rings as their structural units.     

Chemical composition of the organic matter in forest soils: The humus layer

Decomposition and humification were studied within three types of forest humus (mull, moder, and mor) by means of CPMAS ¹³C NMR spectroscopy combined with degradative methods. The NMR data show that O-alkyl carbon decreases in all soils, and alkyl as well as carboxyl carbon increase as depth and decomposition increase; the percentage of aromatic carbon remains constant at about 25%. With increasing depth the amount of carbon that can be identified as belonging to specific compound classes by wet chemical methods decreases from 60% to 40%. Microbial polysaccharides and the proportion of non polysaccharide O-alkyl carbon increase with depth. A selective preservation of recalcitrant, condensed lignin structural units is also observed. In order to relate the spectroscopic and chemical data from investigations of whole soils with studies of humification, samples were fractionated into fulvic acid, humic acid, and humin fractions. The fulvic acid fraction contains large concentrations of carbohydrates irrespective of the soil horizon. The humic acid fraction contains less polysaccharides, but high amounts of alkyl carbon and aromatic structures. The percentage of aromatic carbon existing in the humic acid fraction increases with depth, probably reflecting the amount and degree of oxidative decomposition of lignin. A loss of methoxyl and phenolic groups is evident in the ¹³C NMR spectra of the humic acid fraction. The humin fraction resembles relatively unchanged plant-derived materials as evident from the lignin parameters and carbohydrate contents. All the observed data seem to indicate that humic acids originate form oxidative degradation of humin or plant litter.     

Phosphorus in humus acids

The distribution of phosphorus among humus acid groups in different soil types was studied. It was shown that the binding of P with acid-soluble and-insoluble organic components is determined by the acid-base status of soils, which controls the predominant interaction of P with Fe and Al or with Ca and Mg, and the solubility of the resulting organic phosphates in acid and alkali. The major part of P is associated with the group of humic acids (HAs) in the acid soils and with fulvic acids (FAs) in the neutral and calcareous soils. During the fractionation of organic matter from acid soils, the amount of P redistributed from the HA to the FA group can increase with an increasing acid or alkaline impact on the soil, which breaks the bonds of the phosphorus-bearing organic components with metals.     

不同中药渣组合好氧堆肥产物对土壤碳矿化特性的影响

为研究不同配方中药渣废弃物好氧堆肥产品品质差异及其对土壤碳素矿化的影响，设置了好氧堆肥和有机肥还田两个试验。通过工厂化条垛式好氧堆肥试验，研究了中药渣废弃物3种组合，在相同碳氮比、不同木质纤维素含量下对好氧堆肥产品品质的影响；采用土壤呼吸瓶进行室内恒温恒湿培养模拟土壤施肥效应，研究了3种有机肥施用对不同肥力土壤有机碳分解动态的影响。试验结果显示：中药渣物料的初始木质纤维素含量显著影响堆肥产品的碳氮养分转化和腐殖质组分。与初始低木质纤维素含量处理(T1)相比，高木质纤维素含量处理(T3)堆肥有机碳降解难，堆肥产品中全碳含量提高5.7%，全氮含量降低18.4%，但有利于腐殖质形成，尤其是显著增加胡敏酸组分20.9%。3种中药渣堆肥产品等碳量输入对不同肥力土壤的碳素矿化效果差异显著，高肥力土壤CO₂-C的释放速率和累积释放量均高于低肥力土壤，但有机碳的累积矿化率却低于低肥力土壤，并且高肥力土壤中添加T1堆肥产品累积矿化率显著高于添加T3堆肥产品。两个肥力土壤中有机肥中胡敏酸组分与土壤碳素矿化率之间呈显著负相关关系。因此，为提高有机肥的土壤固碳效应，可适当提高有机肥中胡敏...