Biostimulant activity of humic substances extracted from leonardites

Background and aims

Biostimulants are natural compounds that enhance plant growth and plant nutrient use efficiency. In this study, biostimulant effects of humic substances (HS) extracted from leonardites were analysed on the metabolism of maize plants grown in hydroponic conditions.

Methods

HS extracted from four leonardites were tested for their auxin-like and gibberellin-like activities. Then, 11 day old maize seedlings were treated for 48 h with five concentrations (0, 0.1, 0.5, 1, and 10 mg C L^?1) of HS. After sampling, root growth and morphology, glutamine synthetase (GS) activity, glutamate synthase (GOGAT) activity, total protein content, soluble sugars content, phenylalanine ammonia-lyase (PAL) activity, soluble phenols, and free phenolic acids were analysed.

Results

HS from leonardites had similar spectroscopic pattern, with small differences. The HS from the South Dakota lignite (HS_USA) had more carboxylic groups, whereas the three from Turkish mines had more aromatic and aliphatic structures. HS_USA best enhanced total root growth, root surface area, and proliferation of secondary roots. Plant nutrient use efficiency was enhanced by HS_4, HS_USA and HS_B, with increment of GS and GOGAT enzymes activity and total protein production. HS stimulated also PAL enzyme activity, followed by a higher production of total soluble phenols, p-hydroxybenzoic acid, p-coumarilic acid, and chlorogenic acid.

Conclusion

This study found that, although the activity of the HS depended on the origin of the leonardite, these compounds can be attributed to the biostimulant products, eliciting plant growth, nitrogen metabolism, and accumulation of phenolic substances.

     

Chemical and structural evolution of humic acids during organic waste composting

The effects of the composting process on the chemical and structural properties of humic acids have been studied in seven different organic waste mixtures from different origin. Only slight changes in elemental composition have been found in the humic acids after the composting process pointing to a more aromatic structure with higher proportions of oxygen and nitrogen. Functional groups were the most sensitive to the changes caused by the composting process showing a marked increase in the total acidity and phenolic, carboxyl and carbonyl groups. Gel permeation chromatography showed a slight increase in the average molecular weight of the humic acids. Infrared spectroscopy did not show important differences in humic acid structure but a clear decrease in the intensity of the bands in the region 3000–2850 cm^-1 corresponding to the aliphatic fractions. As a general result, the composting process yields humic acids in which the elemental and functional composition are closer to that of the more humified soil humic acids.     

Molecular-sieve chromatography of humic substances extracted with chelating resin from chernozemic Ah horizons

Summary Humic substances extracted with chelating resin from a Dark Brown Chernozem (Typic Haploboroll) Ah, a Black Chernozem (Udic Haploboroll) Ah, and a Dark Gray Luvisol (Typic Cryoboralf) Ahe were fractionated by Bio-Gel P. The eluted material was combined to form three or four fractions for further characterization.Most of the extracted polydisperse humic substances of the three soils were eluted near V₀ and distributed around a single mean value. The ash content of this material varied from 1.36 to 1.78 per cent. Carboxyl acidity may thus be obtained without interference from any cations.The humic substances from the Dark Brown and Black Chernozem Ah gave similar elution profiles, whereas those from the Dark Gray Luvisol Ahe were less aliphatic and more aromatic in nature. The materials of low molecular weight had the highest content of ash, C, and carboxyl groups. They represented only 3.6 to 14.1 per cent of the C extracted and were considered, on the basis of increased C content, decreased optical density, and infrared spectral configurations, to consist of polynuclear, fused-ring, aromatic structures.     

Characterization of humic materials extracted from hazelnut husk and hazelnut husk amended soils

This study was carried out to determine effects of composted hazelnut husk (CHH) on some chemical properties of soil and soil humic acid (HA). Compost application increases organic matter (OM) content of the soil considerably, OM value of 3.18% became 3.89% in 3 years time interval. Before application of compost, the soil pH was found to be 5.37, while after compost application it became 5.61. FTIR characteristics of humic acid/humic acid-like materials extracted from the original hazelnut husk, composted hazelnut husk and composted hazelnut husk amended soil have been investigated. C and O content of humic acid-like/humic acid materials were in the range of 41.4–50.8% and 37.8–50.5%, respectively. The N content of the humic acid/humic acid-like materials are in the expected range for humic materials which is 2–6%. Comparison of FTIR spectra of hazelnut husk and composted hazelnut husk humic acid-like fractions shows that both exhibit similar but not identical series of IR bands indicating the presence of the same functional groups in both samples. The only difference in the spectra seemed to be a decrement in the peak intensities of composted sample compared to uncomposted one. The similar differentiation of the intensities of IR bands of compost applied soil sample has also been observed. The FTIR spectral results show that the characteristics of composted material tend to become similar to that of soil humic acids characteristics in time.     

Pyrolysis-field ionization mass spectrometry of agricultural soils and humic substances: Effect of cropping systems and influence of the mineral matrix

Whole soil samples, extracted humic substances, the corresponding fulvic (FA) and humic acids (HA) and the extraction residues (humins) from long-term, agricultural test plots were investigated by in-source pyrolysis-field ionization mass spectrometry (Py-FIMS). For the soils distinct differences in the chemical composition of the organic matter in differently managed fields were observed. The FI mass spectra of the extracted humic substances gave complementary chemical information, as they cover a larger mass range compared to the whole soil spectra. The chemical, structural information of the conventional alkaline extraction residues was demonstrated by Py-FIMS spectra to be similar to that of the related soil samples. Influences of mineral matrix to organic matter ratios were studied on mixtures of extracted humic substances with defined mineral components such as quartz, basalt, iron oxide (Fe₂O₃), Ca-montmorillonite, kaolinite and illite. It was shown that in these mixtures the number of mass signals detected and the covered mass range decreased, when organic carbon concentrations (C_org) in this synthetic mineral matrix dropped below 2% (w/w). Limitations in the direct application of Py-FIMS might arise in the case of natural soil samples with C_org concentrations below 0.5% (w/w), high contents of swelling clay minerals and iron oxides. ei]{gnR}{fnMerckx}     

Isolation of protein from humic acid extracted from soil

Summary Chromatography of humic acid in a phenol containing solvent system reveals, in the case of the three types of soil analyzed, the presence of humoprotein containing 11 per cent of nitrogen. Isolation of a humoprotein complex from humic acid, according to the method used by Kirby, followed by paper chromatography allowed the isolation of a protein fraction containing 14.8 per cent nitrogen. This fraction is not dialysable; it has a maximum absorption in ultraviolet light between 260–280 mµ, a small electronegative charge and gives rise to twenty different amino acids. This is the first time that a protein has been separated from humus. Thereby demonstrating that part of the nitrogen contained in humic acid is in the form of protein protected from decomposition.Research supported by the Institut pour l'Encouragement de la Recherche Scientifique dans l'Industrie et l'Agriculture (I.R.S.I.A.).     

Changes in carbon storage in temperate humic loamy soils after forest clearing and continuous corn cropping in France

Soil samples from forest and agricultural sites in three areas of southwest France were collected to determine the effect of forest conversion to continuous intensive corn cropping with no organic matter management on soil organic carbon (C) content. Soils were humic loamy soils and site characteristics that may affect soil C were as uniform as possible (slope, elevation, texture, soil type, vegetation). Three areas were selected, with adjacent sites of various ages of cultivation (3 to 35 yr), and paired control forest sites. The ploughed horizon (0-Dt cm) and the Dt-50 cm layer were collected at each agricultural site. In forest sites, each 10 cm layer was collected systematically down to 1 meter depth. Carbon concentrations were converted to total content to a given depth as the product of concentration, depth of sample and bulk density, and expressed in units of kg m^-2. For each site and each sampled layer, the mineral mass of soil was calculated, in order to base comparisons on the same soil mass rather than the same depth. The pattern of C accumulation in forest soils showed an exponential decrease with depth. Results suggested that soil organic carbon declined rapidly during the first years of cultivation, and at a slower rate thereafter. This pattern of decrease can be fitted by a bi-exponential model assuming that initial soil organic carbon can be separated into two parts, a very labile pool reduced during the first rapid decline and more refractory fractions oxidizing at a slower rate. Sampling to shallow depths (0-Dt cm) resulted in over-estimation of the rate of carbon release in proportion to the initial amount of C, and in under-estimation of the total loss of C with age. The results for the 0–50 cm horizon indicated that losses of total carbon average about 50% in these soils, ranging in initial carbon content from 19 to 32.5 kg m^-2. Carbon release to the atmosphere averaged 0.8 kg m^-2 yr^-1 to 50 cm depth during the first 10 years of cultivation. The results demonstrate that temperate soils may also be an important source of atmospheric carbon, when they are initially high in carbon content and then cultivated intensively with no organic matter management.     

Chemical and physical characterization of lead in three shooting range soils in Florida

Abstract

To better understand the environmental impact of lead (Pb) in shooting range soils, Pb levels in three berm soils were characterized via size distribution, total Pb concentration, water-soluble Pb, sequential extraction and X-ray diffraction (XRD). About 60% of the mid-berm soils of ranges-G and -O existed in grain sizes between 0.5 and 0.25mm (medium sand) while range-L was most abundant in the 0.25–0.106mm (fine sand) size fraction. All three range soils had the most accumulation of lead (60–70%) in the very coarse sand size (2.0–1.0 mm). In ranges-G and -L, the index shows a decreasing Pb enrichment with decreasing particle size, which may be a result of bullet fragmentation and abrasion in shooting range soils. Sequential extractions reveal that ranges-G and -L had the highest proportion of Pb bound to organic matter while range-O was dominated by the carbonate-bound fraction. However, a substantial proportion (one-third) of Pb in soil from the three shooting ranges was associated with carbonates. The XRD result revealed the dominance of carbonates in range-O soil, calcite in range-G soil and metallic lead in ranges-G and -O soil. The conversion of metallic lead to carbonates may be a mechanism for natural attenuation of lead in shooting range soils. Implications for remediation of shooting range soils are further discussed.     

Comparative analysis of environmental DNA extraction and purification methods from different humic acid-rich soils

AIM: To establish a rapid, improved soil environmental DNA extraction and purification protocol. METHODS AND RESULTS: Three different soil DNA isolation and four purification strategies were compared on different soil samples with variable rates of success. Bead beating extraction gave significantly higher DNA yields than microwave-based and liquid nitrogen grinding DNA extraction methods. The inclusion of soil washing prior to cell lysis decreased the amount of purification steps required. Although these soil types differed, polyvinylpolypyrrolidone (PVPP)-sepharose 2B column elution was sufficient for all three samples, yielding DNA pure enough for successful application in molecular studies. One soil sample retained 80% of the initial DNA after successful purification. CONCLUSIONS: Optimization of a purification protocol confirmed that only a combination of previously described methods proved sufficient in yielding pure environmental DNA from humic-rich soils. Total processing time for DNA extraction and subsequent purification from multiple samples was considerably more rapid than the previously described methods. SIGNIFICANCE AND IMPACT OF THE STUDY: This study developed a new optimized soil DNA extraction and purification protocol that is suitable for different environmental sources that are rich in humic acid content.     

Characterizing humic substances from estuarine soils and sediments by excitation-emission matrix spectroscopy and parallel factor analysis

The determination of optical properties of organic matter using spectroscopic techniques is a powerful tool for the characterization of humic substances (HS) in soils and sediments because of sensitivity, specificity and sample throughput. However, basic spectroscopic techniques have practical limitations because of the similarity in the optical properties of many HS. To improve resolution, the combination of excitation-emission matrix (EEM) fluorescence and parallel factor analysis (PARAFAC) was applied for characterizing fulvic acid (FA) and humic acid (HA) fractions from soils and sediments of two estuarine environments in Spain. Five fluorescent components were identified by EEM-PARAFAC and were found in both FA and HA fractions, consistent with the new paradigm of HS as supramolecular associations as well as the ubiquity of the HS components in the environment. Their contribution was, however, different between the FA and HA fractions. Two different, humic-like, fluorescent components were representative of FA and HA fractions, respectively. The spectral characteristics of these components were similar to previously reported PARAFAC components in dissolved organic matter (DOM) in a wide range of environments, suggesting their applicability in assessing OM quality and environmental dynamics. A microbial humic-like component was much more abundant in FA than in HA fractions. Furthermore, principal component analysis clarified that the two identified protein-like components, were enriched in sediment HA compared to soil HA, suggesting a larger contribution of refractory algaenan in sediment HA. The results of the present study demonstrate that EEM-PARAFAC is a useful technique for the biogeochemical characterization of soil and sedimentary HS.     

Hydrolytic enzyme activities of extracted humic substances during the vermicomposting of a lignocellulosic olive waste

Humic substances and three hydrolytic enzymes (beta-glucosidase, phosphatase and urease) were extracted by neutral sodium pyrophosphate from an olive waste (dry olive cake), alone or mixed with municipal biosolids, during a nine month vermicomposting process. Easily degradable compounds decreased during the vermicomposting process because of microbial consumption. When municipal biosolids were added to dry olive cake, microbial activity increased and the amounts of compounds extracted by pyrophosphate were three times lower than olive cake alone. In both instances, beta-glucosidase, phosphatase and urease activities of the organic extracts either increased or remained the same after a nine month period of vermicomposting, thus suggesting that the humus enzyme complexes resisted microbial and earthworm attack. It is known that humus immobilised enzymes also remain active in soil environments, reactivating the nutrient cycles in soil. The use as amendments of vermicomposted olive cake, alone or when mixed with biosolids, could be a good alternative to reactivate the C, P and N-cycles in degraded soils for regeneration purposes.     

Decomposition of organic matter from 36 soils in a long-term pot experiment

The organic matter contents of thirty-six soils were measured annually for twenty years in a pot experiment. The soils originated mainly from arable land and varied in initial organic matter content, texture and pH. The soils were stored at an average air temperature of around 13 °C and every year each soil was mixed thoroughly. Throughout the experiment, soil moisture was kept between 50-70% of its water holding capacity. No organic matter was added during the experiment, so that gross soil organic matter decomposition could be assessed. Relative decomposition rates of soil organic matter decreased as time proceeded. Despite the wide range of soils studied, it was found that during the initial decades, the pattern of soil organic matter degradation was strongly correlated with the organic matter content of the soils at the start of the experiment. This means that during this period the time course of the organic matter content of the soils in our experiment can be estimated from the initial soil organic matter content alone.     

不同母岩发育土壤的可氧化态有机碳

采用KMnO4氧化法测定了8种不同母岩发育形成的土壤的可氧化态有机碳含量,结果表明,发育母岩不同,土壤可氧化态有机碳含量显著不同。通过对土壤养分、土壤颗粒组成、容重与可氧化态有机碳含量的相关性分析表明,土壤可氧化态有机碳与土壤的速效磷、全氮、速效钾、砂粒、粉粒的含量存在着极显著负相关关系;与土壤容重存在着极显著的正相关关系;与土壤的有机质、碱解氮、粗砂、细砂、粘粒、pH值、石砾含量无相关关系。     

Carbon sequestration potential of soils in southeast Germany derived from stable soil organic carbon saturation

Sequestration of atmospheric carbon (C) in soils through improved management of forest and agricultural land is considered to have high potential for global CO₂ mitigation. However, the potential of soils to sequester soil organic carbon (SOC) in a stable form, which is limited by the stabilization of SOC against microbial mineralization, is largely unknown. In this study, we estimated the C sequestration potential of soils in southeast Germany by calculating the potential SOC saturation of silt and clay particles according to Hassink [Plant and Soil 191 (1997) 77] on the basis of 516 soil profiles. The determination of the current SOC content of silt and clay fractions for major soil units and land uses allowed an estimation of the C saturation deficit corresponding to the long‐term C sequestration potential. The results showed that cropland soils have a low level of C saturation of around 50% and could store considerable amounts of additional SOC. A relatively high C sequestration potential was also determined for grassland soils. In contrast, forest soils had a low C sequestration potential as they were almost C saturated. A high proportion of sites with a high degree of apparent oversaturation revealed that in acidic, coarse‐textured soils the relation to silt and clay is not suitable to estimate the stable C saturation. A strong correlation of the C saturation deficit with temperature and precipitation allowed a spatial estimation of the C sequestration potential for Bavaria. In total, about 395 Mt CO₂‐equivalents could theoretically be stored in A horizons of cultivated soils – four times the annual emission of greenhouse gases in Bavaria. Although achieving the entire estimated C storage capacity is unrealistic, improved management of cultivated land could contribute significantly to CO₂ mitigation. Moreover, increasing SOC stocks have additional benefits with respect to enhanced soil fertility and agricultural productivity.     

Biochemical characterization of extracellular polymeric substances extracted from an intertidal mudflat using a cation exchange resin

The biochemical characterization of Extracellular Polymeric Substances (EPS) excreted in a European intertidal mudflat (Marennes–Oléron Bay) was performed. Experiments were carried out for the first time in situ, by using an improved extraction recently developed. This innovative procedure, using a cation exchange resin (Dowex), allows separating precisely different fractions of EPS, especially pure bound EPS. Moreover, it avoids the contamination of EPS fractions by residual and intracellular polymers, enabling to properly estimate polymeric contents in each fraction. The results were partly similar to conventional results described in the literature and the amount of colloidal carbohydrates (146 μg/g of dry sediment) extracted by the Dowex method fitted well with different EPS estimation in European mudflats. Colloidal carbohydrates were essentially composed of glucose (>50%), a carbon source rapidly consumed by the various communities in the sediment. Pure bound carbohydrates were composed of specific carbohydrates (28% rhamnose, 22% xylose). Residual fractions, considered as containing some refractory bound EPS and mostly other internal polymeric substances, presented a more varied composition rich in carbohydrates: galacturonic acid (20%), mannose (19.5%), glucose (19%), arabinose (15%), xylose (8%), galactose (7%).     

Geochemistry of aquatic humic substances in the Lake Fryxell Basin, Antarctica

Dissolved organic carbon (DOC) in Lake Fryxell, 10 streams flowing into the lake, and the moat surrounding the lake was studied to determine the influence of sources and biogeochemical processes on its distribution and chemical nature. Lake Fryxell is an amictic, permanently ice-covered lake in the McMurdo Dry Valleys which contains benthic and planktonic microbial populations, but receives essentially no input of organic material from the ahumic soils of the watershed. Biological activity in the water column does not appear to influence the DOC depth profile, which is similar to the profiles for conservative inorganic constituents. DOC values for the streams varied with biomass in the stream channel, and ranged from 0.2 to 9.7 mg C/L. Fulvic acids in the streams were a lower percentage of the total DOC than in the lake. These samples contain recent carbon and appear to be simpler mixtures of compounds than the lake samples, indicating that they have undergone less humification. The fulvic acids from just above the sediments of the lake have a high sulfur content and are highly aliphatic. The main transformations occurring as these fractions diffuse upward in the water column are 1) loss of sulfur groups through the oxycline and 2) decrease in aliphatic carbon and increase in the heterogeneity of aliphatic moieties. The fraction of modem¹⁴C content of the lake fulvic acids range from a minimum of 0.68 (approximately 3000 years old) at 15m depth to 0.997 (recent material) just under the ice. The major processes controlling the DOC in the lake appear to be: 1) The transport of organic matter by the inflow streams resulting in the addition of recent organic material to the moat and upper waters of the lake; 2) The diffusion of organic matter composed of relict organic material and organic carbon resulting from the degradation of algae and bacteria from the bottom waters or sediments of the lake into overlying glacial melt water, 3) The addition of recent organic matter to the bottom waters of the lake from the moat.