Mineral-organic associations (MOAs) are the basic structural units of soil aggregates and are important reservoirs of nutrients for plants and soil microorganisms, determining the soil structure and fertility. However, the influence of exogenous dissolved organic matter (DOM) chemistry on the stability of MOAs is rarely reported.
Materials and methodsWe first characterized different exogenous DOM through elemental analysis and spectroscopy analysis technologies. Then, a chamber incubation experiment was conducted with DOM addition concentration at 3 g C kg?1 red soil. Principal component analysis, redundancy analysis, and the partial least squares path model were used to better understand the effect of exogenous DOM chemistry on the stability of MOAs.
Results and discussionThe addition of DOM into the red soil significantly increased not only the organic carbon both in the bulk soil and the soil heavy fraction, but also the soil combined humus and the soil mineral-organic compound quantity. Moreover, the rice straw-derived DOM had the best effect on improving the soil mineral-organic compound quantity/degree (additional), followed by the animal-derived DOM, while the fulvic acid increased it the least. The ratios of elements (C/N ratio, O/C ratio, and H/C ratio), aromaticity (SUVA254), and phenolic C content of exogenous DOM had positively significant contributions to the stability of MOAs.
ConclusionsThe rice straw-derived DOM had the greatest enhancement on the stability of the MOAs for its higher C/N ratio and phenolic groups content, so the exogenous DOM characteristics could be as an indicator in predicting the stability of the MOAs and evaluating the soil fertility.
相似文献Purpose
Dissolved organic matter (DOM), a heterogeneous mixture of low concentrations of organic matter draining from soils, plays a significant role in soil C cycling and in nutrient and pollutant transport. DOM from undisturbed soil profiles has rarely been studied. Hydrophobic acids (Ho) and hydrophilic acids (Hi), the major components of DOM, were recovered, using XAD-8 and XAD-4 resins in series, from waters draining in winter and in spring periods from well-drained and poorly drained Irish grassland soil profiles in lysimeters.Materials and methods
Waters were collected from 45 soil undisturbed lysimeters at the Teagasc Research Centre, Johnstown Castle, Wexford, Ireland. Four Irish representative soils had been collected as undisturbed 1.0-m-deep monoliths, transported to the experiment site and arranged randomly in an experimental facility. Water collections were carried out in winter and spring periods. The DOM was isolated and fractionated using an XAD-8 and XAD-4 resins in-tandem procedure, and hydrophobic acids (Ho) and hydrophilic acids (Hi) were isolated.Results and discussion
The amounts of DOM recovered in the winter period were much greater than those in the spring period, and the soil types had only minor influences on the DOM concentrations recovered. The Ho and Hi fraction contents ranged from 62 to 90 and 10 to 28%, respectively, of the total DOM content extracted. The Hi acids were most enriched in 13C, and considered to reflect greater microbial inputs. The neutral sugar (NS) contents for the Ho and Hi fractions were in the range of 15 to 52 μg mg?1, with the Hi fraction most enriched. The amino acids (AAs) for the Ho and Hi fractions varied from 0.6 to 2.4%, and the total AAs and NS of the Ho acids were well correlated. The DOM fractions from the drainage waters contained much less AAs and NS than the corresponding fractions in the parent soils. The solid- and liquid-state NMR data indicated organic structures with low aromaticity, significant amounts of carbohydrate and with lesser amounts of peptide structures, and with long-chain methylene (CH2)n and methine (-CH-) groups.Conclusions
The application of a variety of wet chemistry and of spectroscopy procedures has given a more in-depth awareness of the compositions of the DOM in the drainage waters from four different soils in 1.0-m-deep lysimeter arrangements. Based on wet chemistry analyses, and FTIR and liquid- and solid-state NMR spectrometry, it is clear that there are some differences between the compositions of the DOM fractions recovered. Alkyl functionalities dominated the structures. These included significant amounts or O-alkyl (predominantly carbohydrate), and with lesser (and variable amounts in the different fractions) aromatic structures (to which aromatic amino acid components were considered to be significant contributors), and with no evidence for lignin-derived structures The results suggest that, during residence in the soil solution, microbiological processes transform the SOM components released into products that are greatly different from their materials of origin in the SOM.Purpose
Soil dissolved organic matter (DOM) as the labile fraction of soil organic carbon (SOC) is able to facilitate biogeochemical redox reactions effecting soil respiration and carbon sequestration. In this study, we took soil samples from 20 sites differing in land use (forest and agriculture) to investigate the electron transfer capacity of soil DOM and its potential relationship with soil respiration.Materials and methods
DOM was extracted from 20 soil samples representing different land uses: forest (nos. 1–12) and agriculture (nos. 13–20) in Guangdong Province, China. Chronoamperometry was employed to quantify the electron transfer capacity (ETC) of the DOM, including electron acceptor capacity (EAC) and electron donor capacity (EDC), by applying fixed positive or negative potentials to a working electrode in a conventional three-electrode cell. The reversibility of electron accepting from or donating to DOM was measured by applying switchable potentials to the working electrode in the electrochemical system with the multiple-step potential technique. Carbon dioxide produced by soil respiration was measured with a gas chromatograph.Results and discussion
Forest soil DOM samples showed higher ETC and electron reversible rate (ERR) than agricultural soil DOM samples, which may be indicative of higher humification rate and microbial activity in forest soils. The average soil respiration of forest soil (nos. 1–12) and agricultural soil (nos. 13–10) was 26.34 and 18.58 mg C g?1 SOC, respectively. Both EDC and EAC of soil DOM had close relationship with soil respiration (p?<?0.01). The results implied that soil respiration might be accelerated by the electroactive moieties contained in soil DOM, which serve as electron shuttles and facilitate electron transfer reactions in soil respiration and SOC mineralization.Conclusions
DOM of forest soils showed higher ETC and ERR than DOM of agricultural soils. As soil represents one of the largest reservoirs of organic carbon, soil respiration affects C cycle and subsequently CO2 concentration in the atmosphere. As one of the important characteristics of soil DOM related to soil respiration, ETC has a significant impact on greenhouse gas emission and soil carbon sequestration but has not been paid attention to. 相似文献Purpose
The objective of this study was to evaluate the effect of the physicochemical properties of five dissolved organic matter (DOM) isolates on their reactivity with the hydroxyl radical (HO·) in water.Materials and methods
Five DOM isolates were purchased from the International Humic Substance Society (IHSS). Weight average molecular weight (M W) of these samples was quantified using size exclusion chromatography based on polyethylene glycols as reference standards. Functional group and elemental composition of the DOM samples were available from the IHSS website. Room temperature rate constants were measured using electron pulse radiolysis.Results and discussion
Five IHSS standards were examined in this study: two soil organic and three aquatic organic matters. The composition varied from samples that had primarily aliphatic carbon (Pony Lake fulvic acid) to mostly aromatic carbon moieties (Elliot Soil humic acid). The M W values of the five samples ranged from 2,400 to 4,100 Da, with an average value of 3,060 Da. Second-order reaction rate constants between DOM and HO· (k DOM-HO·) were measured using thiocyanate competition kinetics, giving values ranging from 1.21 to 10.36?×?108 MC ?1?s?1. The k DOM-HO· values were not found to correlate with either M W or the aliphatic-aromatic carbon ratio, which is consistent with previous reports looking at natural organic matter (NOM), but is different to reports on size-fractionated (ultrafiltration through 15–1 kDa membranes) effluent organic matter (EfOM). We attribute this difference to the larger molecular weight distributions in size-fractionated EfOM compared to NOM.Conclusions
The k DOM-HO· values in this study ranged over a factor of 10, suggesting that hydroxyl radical reactivity does depend on the sample composition; however, no major correlation was found between the measured reactivity and bulk physicochemical properties of DOM. 相似文献To compare Cd removal from different soils with three washing agents recovered from sewage sludge (dissolved organic matter (DOM), soluble humic-like substances (HLS), soluble humic substances (SHS)). Also, to investigate how washing with these agents changes soil organic-matter composition (OM).
Materials and methodsSandy clay loam (S1) and clay (S2) highly contaminated with Cd (300 mg kg?1) were washed with DOM, HLS, or SHS solutions at various pHs, and with various washing times and washing modes (single or double). Cd distribution and OM composition were determined (including content of humic substances (HS), fulvic fraction (FF), labile humic acids (L-HA), and stable humic acids (S-HA)).
Results and discussionCd removal proceeded with pseudo-second-order kinetics. Equilibrium was reached in 30 min (S1) and 60 min (S2). DOM, HLS, and SHS removed 75–82% of Cd from S1, and 80–87% from S2. The most mobile fraction of Cd was removed after one wash. S2 retained more OM, including HS, than S1. Although washing did not change the HA/FF ratio in most variants, washing with DOM and HLS increased the percentage of L-HA in both soils. Washing with SHS increased S-HA content in both soils, but the percent content of S-HA was similar to that in the unwashed soil.
ConclusionsDOM, HLS, and SHS derived from sewage sludge can effectively remediate clay and sandy clay soils highly contaminated with Cd. Washing with an SHS solution can increase the content of the most stable carbon forms (HA), which is beneficial for carbon sequestration in remediated soils.
相似文献Crop straw return into arable land is a common method of disposing of excess straw in China and can improve soil dissolved organic matter (DOM) that is known to modify soil zinc (Zn) extractability and mobility.
Materials and methodsWe conducted a soil box (internal dimensions, 160?×?140?×?80 mm3) experiment to evaluate the response of Zn extractability and transfer by diffusion to DOM after maize straw amendment (St, 0 and 15 g kg?1) in calcareous soil treated with ZnSO4·7H2O (Zn, 0 and 20 mg kg?1). Soil treated with St0Zn0 (control), St15Zn0, St0Zn20, or St15Zn20 was isolated in the 10-mm center of the box, and untreated soil was placed in compartments at either side.
Results and discussionResults revealed that addition of St0Zn20 or St15Zn20 increased the concentration of Zn extracted with diethylenetriaminepentaacetic acid (DTPA-extractable Zn) in the central layer compared with control or addition of St15Zn0. Over the course of 45 days, transfer of DTPA-extractable Zn into the adjacent untreated soil was detected at 15–20 mm in soil with St15Zn20 but at 10–15 mm with St0Zn20 and only 0–5 mm with St15Zn0. Additionally, a higher amount of DTPA-extractable Zn transfer into the adjacent untreated soil also occurred in St15Zn20. This increased DTPA-extractable Zn transfer may be associated with the formation of Zn-fulvic acid complexes with the provision of DOM derived from straw.
ConclusionsSoluble Zn combined with straw return may be a promising strategy for improving both Zn mobility and extractability in calcareous soil.
相似文献The quantification of spatial patterns of soil respiration (RS) is an important step in modelling soil carbon budgets. This study aims to characterise the spatial variability of RS using traditional and geostatistical analyses in a mature temperate forest during the growing season, with emphases on temporal variation in the spatial patterns and soil properties and stand structural parameters driving the variability of RS.
Materials and methodsRS, soil temperature and soil water content were sampled at 780 positions in a 9.12-ha permanent plot in a spruce-fir valley forest in the spring, summer and autumn of 2015. Furthermore, edaphic properties were measured adjacent to each sampling point, and all trees with DBH (diameter at breast height of tree) greater than 1 cm were mapped in the plot.
Results and discussionRS showed strong spatial variation across the three measurement campaigns, with the autocorrelation length ranging from 10 to 17 m. The spatial variability of RS in the spring period was relatively higher than that of summer and autumn. Soil water content was confirmed to be the primary factor driving spatial RS, followed by soil temperature, soil organic carbon, total nitrogen, C:N, pH and the maximum DBH within radius of 4 m of sampling points. The multiple regression model fitted by soil properties and stand structural parameters could account for 11–32% of the spatial variation of RS. However, the involved factors in the regression model varied with season, and soil temperature was more important in controlling the spatial variability of RS in the spring period.
ConclusionsThe study highlights that soil water content and soil temperature play the most important role in determining the spatial patterns of RS across the growing season.
相似文献Several interactions between Al and the solid phase of soil influence Al buffering in soil solution. This work evaluated soils cultivated with Pinus taeda L. to determine Al forms in organic and mineral horizons using various extraction methods and to relate acidity with clay mineralogy.
Materials and methodsOrganic and mineral horizons of 10 soil profiles (up to 2.1 m deep) in southern Brazil were sampled. Organic horizons were separated into fresh, aged, and fermented/humified litter. The following Al extraction methods were utilized: 0.5 mol L?1 pH 2.8 CuCl2–Al complexed in organic matter; 1.0 mol L?1 KCl–exchangeable Al; water–Al soluble in soil solution; HF concentrated?+?HNO3 concentrated?+?H2O2 30% (v/v)–total Al. Six sequential extractions were carried out to isolate different forms of amorphous minerals that can buffer Al on soil solution: 0.05 and 0.1 mol L?1 sodium pyrophosphate; 0.1 and 0.2 mol L?1 ammonium oxalate; 0.25 and 0.5 mol L?1 NaOH. Samples of clay were also analyzed by XRD.
Results and discussionThere was a clear effect of litter age on increasing total Al concentration. In the aged litter and fermented and/or humified litter, levels of total Al were 1.4 to 3.8 and 1.5 to 7.8 times greater than in fresh litter, respectively. The CuCl2 method had higher Al extraction capacity than the KCl method for litter. The lowest Al–pyrophosphate values were observed in the Oxisol, which also had a predominance of gibbsite and the lowest levels of Al–KCl and Al–CuCl2. There was an inverse relationship between degree of soil weathering and soluble and exchangeable Al in soils. Available Al increased with higher Si proportion in minerals of the clay fraction (2:1?>?1:1?>?0:1).
ConclusionsThe worst scenario was soils with the combination of high soluble and exchangeable Al levels and high concentrations of amorphous forms of Al minerals. The best predictors of Al accumulation in the youngest litter horizon were extractions of amorphous minerals with pyrophosphate and NaOH. These extractors are normally used to predict the level of Al buffering in soils. Organic matter had less influence on Al dynamics in soils.
相似文献The aim of this meta-analysis was to investigate the interactive effects of environmental and managerial factors on soil pH and crop yield related to liming across different cropping systems on a global scale.
Materials and methodsThis study examined the effects of liming rate, lime application method, and liming material type on various soil chemical properties and crop yield based on data collected from 175 published studies worldwide since 1980.
Results and discussionThe most important variables that drive changes in soil pH and crop yield were liming rate and crop species, respectively. Soil conditions, such as initial soil organic matter and soil pH, were more important for increasing soil pH in field-based experiments, while lime material type and application method were more important for improving crop yield. To effectively neutralize soil acidity, the optimum liming duration, rate, and material type were?<?3 years, 3–6 Mg ha?1, and Ca (OH)2, respectively. Averaged across different crop species, the application of CaO, CaCO3, Ca (OH)2, and CaMg (CO3)2 increased yield by 13.2, 34.3, 29.2, and 66.5%, respectively.
ConclusionsThis meta-analysis will help design liming management strategies to ameliorate soil acidity and thus improve crop yield in agroecosystems.
相似文献