Soil phosphorus characterisation by 31p nuclear magnetic resonance

Abstract

Five New Zealand topsoils, including three sampled under introduced pasture and two in native tussock grasslands, were extracted with 0.5 M NaOH, and the different classes of phosphorus compounds in the extracts distinguished by ³¹p nuclear magnetic resonance (n.m.r.).

Inorganic orthophosphate and orthophosphate monoesters were the major forms of phosphorus in all soil extracts. The tussock‐grassland soil extracts showed the greatest diversity of phosphorus forms, and included compounds with n.m.r. signals ascribed to phosphonates, a previously unreported form of soil phosphorus.     

Influence of conifers on the forms of phosphorus in selected New Zealand grassland soils

We examined the effects of conifers on the forms of P in low-fertility tussock grassland soils using ³¹P nuclear magnetic resonance (NMR) and soil P fractionation. Results from field and glasshouse experiments clearly demonstrated that conifers enhanced the mineralization of labile (and to a lesser extent more resistant) forms of soil organic P which, in turn, increased amounts of labile inorganic P in the soil. These findings have important implications for P availability and long-term sustainable management of grassland soils in New Zealand.     

Characterisation of organic phosphorus in overland flow from grassland plots using 31P nuclear magnetic resonance spectroscopy

Grazing animals are known to change the characteristics of agricultural grasslands as a source of and pathway for phosphorus (P) loss to water. Previous work, using physico-chemical analysis of the overland flow revealed that the presence of grazing animals increased the overall quantity of P being lost, in particular the unreactive and particulate P fractions. The aim of this study was to characterise the organic P (Po) fraction in overland flow from grazed and non-grazed grassland small plots using phosphorus-31 nuclear magnetic resonance (³¹P NMR) spectroscopy to give greater insight into P loss to water under simulated rainfall. The effect of the grazing animal was most pronounced in the dissolved unreactive P (DUP) and particulate unreactive P (PUP) fractions measured in overland flow from the grazed plots, over four times higher than from the non-grazed plots. Five distinct classes of P compounds were detected in the ³¹P NMR spectra, inorganic orthophosphate (δ = 6.83 ppm), orthophosphate monoesters (δ = 4.95–5.69 ppm), orthophosphate diesters (δ = 1.89 ppm), phosphonates (δ = 19.38 ppm), and pyrophosphates (δ = −3.26 ppm). Distinct signals at 5.69, 5.37, 5.10, and 4.95 ppm in the overland flow extracts from the plots indicated significant concentrations of myo -inositol hexakisphosphate in the orthophosphate monoester region. Orthophosphate diesters (assigned to phospholipids) and phosphonates were also only detected in overland flow collected from the grazed plot. These results indicate that normal grazing management practices may not only affect the concentrations of Po but also the forms of Po being transferred from grassland systems to water.     

Assessing the organic phosphorus status of an Oxisol under tropical pastures following native savanna using 31P NMR spectroscopy

³¹P nuclear magnetic resonance (NMR) spectroscopy, P fractionation, and a P sorption experiment were used to follow the changes in P in the A horizons (0–10 cm) of acid savanna soils, Colombia, after little P fertilization and 15 years' continuous growth of a grass (Brachiaria decumbens) and a grass/legume (B. decumbens+Pueraria phaseoloides) pasture. Ready P supply as analyzed by Bray P was low under native savanna (1.3 mg kg^-1 soil) and responded moderately on pasture establishment. Concurrently, the affinity of the soil for inorganic P declined slightly after pasture establishment. ³¹P NMR spectroscopy revealed that P associated with humic acids was dominated by monoester P followed by diester P. Smaller proportions were observed for phosphonates, teichoic acid P, orthophosphate, and pyrophosphate. P associated with fulvic acids had lower proportions of diester P and higher contents of orthophosphate. Under native savanna the reserves of labile organic P species (phosphonates and diester P including teichoic acid P) associated with humic and fulvic acids were 12.4 and 1.1 kg ha^-1, respectively, and increased to 18.1 and 1.8 kg ha^-1 under grass pasture, and to 19.5 and 2.3 kg ha^-1 under grass/legume pasture. These data emphasize the importance of labile organic P species in the P supply for plants in improved tropical pastures, and further indicate that humic acid P in particular responds to land-use changes within a relatively short time-scale. Earthworm casts were highly abundant in the B. decumbens+P. phaseoloides plot and were enriched in labile organic P species. We conclude that earthworm activity improves the P supply in soil under tropical pastures by creating an easily available organic P pool.Dedicated to Professor J.C.G. Ottow on the occasion of his 60th birthday     

Improving Sensitivity of Solution 31P NMR Analysis in Australian Xeralfs

Phosphorus-31 nuclear magnetic resonance (³¹P NMR) spectroscopy is widely used to identify and quantify phosphorus (P) forms in soil. This study aimed to determine whether narrowing the soil to extractant sodium hydroxide–ethylenediaminetetraacetic acid (NaOH-EDTA) ratio from 1:20 to values as low as 1:4 would improve sensitivity of solution ³¹P NMR spectroscopy without degrading resolution or quantitation. Four Australian soils were tested using four ratios. The narrowest ratio of 1:4 gave the best quality NMR spectra in terms of signal-to-noise ratio. Peak resolution was not degraded on narrowing the ratio. There was no clear effect of narrowing the extraction ratio on extraction efficiency or the distribution of signal among chemical shift regions (orthophosphate, monoester P, diester P, and pyrophosphate). We conclude that a ratio of 1:4 improved NMR analysis for these particular soils and should be considered for other soils, particularly low-P soils, where NMR sensitivity is limiting.     

Properties of dissolved organic matter related to soil organic matter quality and nitrogen additions in Norway spruce forest floors

The quality of dissolved organic matter (DOM) is highly variable and little information is available on the relation of DOM quality to the structure and composition of its parent soil organic matter (SOM). The effect of increasing N inputs to forest soils on the structure and composition of both SOM and DOM also remains largely unclear. Here we studied the release of DOM, its specific UV absorption and two humification indices (HIX) derived from fluorescence spectra from Oa material of 15 North- and Central-European Norway spruce (Picea abies (L.) Karst.) stands. The Oa material was incubated aerobically at 15 °C and water holding capacity over a period of 10 months and extracted monthly with an artificial throughfall solution. Soil respiration was determined weekly. The influence of mineral N inputs on composition of DOM and on respiration rates was investigated on periodically NH₄NO₃-treated Oa samples of eight selected sites. Release of dissolved organic carbon (DOC) from untreated Oa material samples ranged from 0.0 to 58.6 μg C day⁻¹ g C⁻¹ and increased with increasing C-to-N ratio. One HIX and UV absorption of DOM were negatively correlated to the degree of oxidation of lignin-derived compounds and positively to the C-to-N ratio and – HIX only – to the aromatic C content of SOM. Mineral N addition had no distinct effect on respiration rates. In six of eight samples the N-treatment caused an increase in specific UV absorption or one HIX of DOM. However, these effects were not statistically significant. Addition of mineral N did not affect the rates of DOM release. Our results show that properties of SOM largely determine the amount and quality of DOM in forest floors. Changes of DOM quality due to mineral N additions are likely, but we cannot confirm significant changes of DOM release.     

Quantification and bioavailability of scyllo-inositol hexakisphosphate in pasture soils

The recent identification of scyllo-inositol hexakisphosphate in alkaline soil extracts by solution ³¹P NMR spectroscopy allowed us to investigate this compound in soils by re-analyzing spectra from two previously published studies. Concentrations of scyllo-inositol hexakisphosphate in 29 temperate pasture soils from England and Wales ranged between 11 and 130 mg P kg⁻¹ soil and accounted for between 4 and 15% of the soil organic phosphorus. The ratio of scyllo-inositol hexakisphosphate to myo-inositol hexakisphosphate ranged between 0.29 and 0.79. In a 10 month pot experiment with six grassland soils from New Zealand, growth of pine seedlings (Pinus radiata D. Don) decreased scyllo-inositol hexakisphosphate concentrations by between 10 and 46%. Growth of ryegrass (Lolium perenne L.) decreased scyllo-inositol hexakisphosphate in three low-nutrient soils by 5-21%, but increased it in three other soils by 11-16%. We conclude that scyllo-inositol hexakisphosphate is an important component of soil organic phosphorus with potential ecological significance.     

Changes in properties of soil-derived dissolved organic matter induced by biodegradation

Properties of dissolved organic matter (DOM) determine its biodegradation. In turn, biodegradation changes the properties of the remaining DOM, which may be decisive for the formation of stable organic carbon in soil. To gain information on both mechanisms and controlling factors of DOM biodegradation and the properties of biodegraded DOM, we investigated changes in the composition of 13 different DOM samples extracted from maize straw, forest floors, peats, and agricultural soils during a 90-day incubation using UV absorbance, fluorescence emission spectroscopy, FTIR-spectroscopy, ¹H-NMR spectroscopy, pyrolysis-field ionization mass spectroscopy (Py-FIMS), and ¹³C natural abundance before and after incubation. Changes in the DOM properties were related to the extent of biodegradation determined by the release of CO₂. Increasing UV absorption and humification indices deduced from fluorescence emission spectra, and increasing portions of aromatic H indicated relative enrichment of aromatic compounds during biodegradation. This enrichment significantly correlated with the amount of DOC mineralized suggesting that aromatic compounds were relatively stable and slowly mineralized. ¹³C depletion during the incubation of highly degradable DOM solutions indicated an enrichment of lignin-derived aromatic compounds. Py-FI mass spectra indicated increasing contents of phenols and lignin monomers at the expense of lignin dimers and alkylaromatics during incubation. This partial degradation of higher-molecular, lignin-derived DOM compounds was accompanied by relative increases in the proportions of lower-molecular degradation products and microbial metabolites. Carbohydrates, especially when abundant at high initial contents, seem to be the preferred substrate for microorganisms. However, four independent methods suggested also some microbial production of carbohydrates and peptides during DOM degradation. After incubation, the composition of highly degradable DOM samples became similar to relatively stable DOM samples with respect to aromaticity, carbohydrate content, and thermal stability. We conclude that DOM biodegradation seems to result in organic matter properties being a precondition for the formation of stable carbon. These structural changes induced by DOM biodegradation should also result in stronger DOM sorption to the soil matrix additionally affecting DOM stabilization.     

Composition of the organic phosphorus fraction in basidiocarps of saprotrophic and mycorrhizal fungi

In our screening, we aimed to detect phosphonates and other forms of organic phosphorus in basidiocarps and vegetative mycelia of six common basidiomycetes. Organic phosphorus-containing compounds were extracted in alkali and analysed using ³¹P NMR. Monoesters, diesters, pyrophosphates and polyphosphates detected in high amounts reflected the high metabolic activity in basidiocarps (growth, production of basidiospores). Phosphonates were present in all samples, in concentrations ranging from 14 mg kg⁻¹ of the extracted phosphorus in Boletus badius basidiocarp to 140 mg kg⁻¹ in Amanita muscaria vegetative mycelium. Detection of phosphonates in basidiocarps together with our previous evidence from laboratory experiments support the fungal production of natural phosphonates in forest ecosystems.     

Temporal changes in humic acids in cultivated soils with continuous manure application

Abstract

Although the application of manure to upland fields is believed to induce changes in the quality of humic substances in soil as well as the quantity, the direction and extent of these changes have not been elucidated. To understand temporal variations in humic acids, periodically collected soil samples from two fields, a Typic Hapludult (Togo) and a Pachic Melanudand (Kuriyagawa), with cattle manure and chemical fertilizer (CF) were examined. The content and degree of humification (darkening) of the humic acids were distinctly greater in Kuriyagawa than in Togo soil. Corresponding to the difference in the degree of humification, molecular size distribution, elemental composition, infrared (IR) spectra, and ¹³C cross polarization/magic angle spinning nuclear magnetic resonance (CPMAS NMR) spectra of humic acids differed between the two soils. Manure application at 40 Mg ha^?1 year^?1 for 16 years (Togo) and at 80 or 160 Mg ha^?1 year^?1 for 19 years (Kuriyagawa) resulted in greater humic acid content compared with plots with CF only because of its increase in the manured plots and/or decrease in the CF plots. Manure application at an extremely high rate (160 Mg ha^?1 year^?1) resulted in higher H content and greater signal intensities of alkyl C, O-alkyl C and amide C=O in the ¹³C CPMAS NMR and/or IR spectra. Although humic acids with larger molecule sizes increased in all the manured plots, differences between the humic acids from the plots with and without manure applied at practical levels in the elemental and spectroscopic analyses were small or scarce. These results were considered to be because of the similarity between the indigenous soil humic acids and the manure-derived ones in Togo soil (a low degree of humification) and because of the abundance of highly-humified humic acids in Kuriyagawa soil.     

Stabilization of dissolved organic matter by sorption to the mineral soil

The main process by which dissolved organic matter (DOM) is retained in forest soils is likely to be sorption in the mineral horizons that adds to stabilized organic matter (OM) pools. The objectives of this study were to determine the extent of degradation of sorbed OM and to investigate changes in its composition during degradation. DOM of different origins was sorbed to a subsoil and incubated for 1 year. We quantified mineralized C by frequent CO₂ measurements in the headspace of the incubation vessels and calculated mean residence times by a double exponential model. Mineralization of C of the corresponding DOM in solution was used as a control to estimate the extent of DOM stabilization by sorption. Changes in the composition of sorbed OM during the incubation were studied by spectroscopic (UV, fluorescence) and isotope (¹³C, ¹⁴C) measurements after hot-water extraction of OM.The fraction of sorbed organic C mineralized during the incubation was only one-third to one-sixth of that mineralized in solution. The mean residence time of the most stable OM sample was estimated to increase from 28 years in solution to 91 years after sorption. For highly degradable DOM samples, the portion of stable C calculated by a double exponential model nearly doubled upon sorption. With less degradable DOM the stability increased by only 20% after sorption. Therefore, the increase in stability due to sorption is large for labile DOM high in carbohydrates and relatively small for stable DOM high in aromatic and complex molecules. Nevertheless, in terms of stability the rank order of OM types after sorption was the same as in solution. Furthermore, the extent of sorption of recalcitrant compounds was much larger than sorption of labile compounds. Thus, sorptive stabilization of this stable DOM sample was four times larger than for the labile ones. We conclude that stabilization of OM by sorption depends on the intrinsic stability of organic compounds sorbed. We propose that the main stabilization processes are selective sorption of intrinsically stable compounds and strong chemical bonds to the mineral soil and/or a physical inaccessibility of OM to microorganisms. The UV, fluorescence and ¹³C measurements indicated that aromatic and complex compounds, probably derived from lignin, were preferentially stabilized by sorption of DOM. The ¹³C and ¹⁴C data showed that degradation of the indigenous OM in the mineral soil decreased after sorption of DOM. We estimated DOM sorption stabilizes about 24 Mg C ha⁻¹ highlighting the importance of sorption for accumulation and preservation of OM in soil.     

土壤磷形态组分分级及31P-NMR 技术应用研究进展

农田生态系统中土壤磷形态转化,影响土壤磷对作物的有效供应。土壤磷分为无机磷和有机磷两大部分。化学连续提取法 (chemical sequential fractionation,CSF) 研究土壤磷形态分级,采用不同的化学提取剂,分级提取土壤中组成或分解能力接近的有机无机含磷化合物,是目前表征土壤磷素形态的重要方法。但该方法虽历经改进,仍难以确切反映土壤磷的实际组成,提取的不同磷形态间存在重叠,有机磷和无机磷组分分级存在一定的误差;不同分级磷组分对作物的有效性,需谨慎评估。核磁共振波谱技术 (nuclear magnetic resonance,NMR) 根据核磁共振波谱图上共振峰的位置、强度和精细结构来研究土壤中含磷化合物的分子结构。液相31P-NMR 可以同吋检测出土壤中多种磷组分,如正磷酸盐、磷酸单酯、磷酸二酯、膦酸脂、焦磷酸盐和多聚磷酸盐,识别土壤提取物磷形态,可将有机磷与无机磷分开。本文综述了应用31P-NMR 技术研究土壤磷形态组分的一些进展,总结了样品制备过程、NMR 测试参数及在土壤磷形态转化研究中的应用。二维31P-NMR 技术发展为鉴定分析土壤中更多种类的含磷化合物提供了契机。     

Phosphorus speciation and colloidal phosphorus responses to short-term cessation of fertilization in a lime concretion black soil

Long-term excessive application of mineral fertilizer has led to soil acidification and phosphorus(P) accumulation, increasing the risk of P loss and environmental pollution, and cessation of fertilization is widely considered as a cost-effective management strategy to relieve this situation; however, how such cessation influences P speciation and concentrations in a bulk soil and colloidal fractions and whether decreasing P concentration might maintain soil fertility remain unclear. In this stu...     

Responses of soil phosphorus pools accompanied with carbon composition and microorganism changes to phosphorus-input reduction in paddy soils

In rice-wheat rotation systems, changes in soil phosphorus(P) pools and microorganisms in rice-growing seasons have been studied;however, further investigations are required to test whether these indexes exhibit different responses in wheat-growing seasons. Additionally, such studies need to include potential variations in soil carbon(C) structure and microbial community composition. In this study, a long-term rice-wheat rotation P-input reduction experiment was conducted to observe the variations in soil P pools and C composition in the 7th wheat season and to investigate the responses of soil enzyme activity and microbial communities. Four P fertilization treatments were included in the experiment, i.e., P application for rice season only(PR), for wheat season only(PW), and for both rice and wheat seasons(PR+W) and no P application in either season(Pzero). Compared with PR+W treatment, Pzero treatment significantly decreased(P < 0.05) labile and stable P pools. Different P fertilization regimes altered soil microbial community composition and enzyme activity, whereas C composition did not vary. However, PW treatment resulted in relatively more O-alkyl-C than PR treatment and the highest number of microorganisms. Besides, the higher ratios of fungi/bacteria and Gram-positive bactetia/Gram-negative bactetia were related to labile C pools, particularly O-alkyl-C, as opposed to recalcitrant C. Our results clarified the status of soil P pools, C chemistry, and the response of microorganisms under dry-farming conditions in the P input-reduced rice-wheat rotation system.     

利用NMR技术测定小麦胚芽中的脂质成分

为深入探究小麦胚芽中的脂质成分,该研究采用不同溶剂分别提取小麦胚芽中的磷脂和中性脂质,利用核磁共振技术 （nuclear magnetic resonance,NMR）对小麦胚芽中的脂质成分进行分析,结果表明：³¹P NMR在小麦胚芽中检测到6种磷脂和相对应的5种溶血性磷脂,以及非脂质含磷化合物甘油磷脂酰胆碱（GPC）;磷脂中含量最高的是磷脂酰胆碱(PC),其摩尔浓度为0.42 μmol/g,摩尔分数为28.50%,质量浓度为0.31 mg/g,质量分数为30.2%;¹H NMR测定小麦胚芽中的多种中性脂质组成及含量,包括甘油三酯（TG）、甘油二酯（DG）、甘油单酯（MG）和游离脂肪酸（FA）,其中含量最高的甘油酯是TG,占比为77.25%,含量最低的是2-甘油单酯（2-MG）,占比为0.03%;小麦胚芽的甘油三酯和磷脂中检测出亚油酸（L）、油酸（O）和亚麻酸（Ln）等6种不饱和脂肪酸,其中亚油酸的含量最高,在甘油三酯中占比56.26%,在磷脂中占比45.37%。溶血性磷脂和GPC是磷脂的水解产物,DG、MG和FA是甘油三酯的水解产物,这些物质可以反映样品中脂质的水解程度。研究结果表明,利用NMR不仅能够对小麦胚芽脂质的组分进行定性定量分析,而且可以监测小麦胚芽脂质水解程度的变化。NMR技术在小麦胚芽相关产品的脂质分析研究具有重要作用。     

Effects of tillage and crop rotation on chemical phosphorus forms and some related biological activities in a Chilean Ultisol

The effect of tillage systems and crop rotation on microbial biomass phosphorus (MBP) and acid phosphatase (P‐ase) activity, and the amount of different phosphorus (P) forms measured by ³¹P‐NMR spectroscopy were studied on a field experiment carried out in a temperate Ultisol from southern Chile. Two tillage systems, no tillage (NT) and conventional tillage (CT) and two crop rotations, oat–wheat (OW) and lupine–wheat (LW) were evaluated 4 yr after the start of the experiment to determine the effects of such management on some soil biological parameters and P forms at three depths (0–5, 0–10 and 10–20 cm). Microbial biomass P ranged from 6.5 to 22.6 mg/kg, whereas the mean total P (P_T) was 1995 mg/kg for all treatments (OW and LW). Microbial biomass carbon (MBC) and surface P accumulation (at 0–5 cm depth), including Olsen P, MBP, orthophosphate monoesters (monoester‐P), were larger under NT than CT. Tillage effects were greater than crop rotation effects in enhancing P availability. The LW rotation showed enhanced P‐ase activity and increased monoester‐P forms (57 vs. 30% of the total integral area of the spectra, in average) compared with OW. Nevertheless, OW rotation increased orthophosphate (ortho‐P), especially at 10–20 cm. Microbial biomass carbon ranged from 532 to 2351 mg/kg, which represented 1.2–4.5% of total organic C (C_o). Furthermore, MBP correlated positively with MBC (r = 0.80), Olsen P (r = 0.77), C_o (r = 0.77), pH (r = 0.65), P_T (r = 0.65) and P‐ase activity (r = 0.57), suggesting the importance of the microbial biomass on soil P availability.     

Isolation and characterization of labile organic phosphorus pools in soils from the Askov long‐term field experiments

Isolierung und Kennzeichnung des labilen organischen Phosphor‐Pools in Böden des Langzeitdüngungsexperimentes Askov Labiler organischer Phosphor (P_o) im Boden spielt eine wichtige Rolle in der P‐Ernährung der Pflanzen und ist bedeutend hinsichtlich der Gewässereutrophierung. Im Rahmen dieser Arbeit werden neuere Ergebnisse zu den Eigenschaften des labilen P_o und seiner Reaktion auf unterschiedliche Düngungssysteme diskutiert. Die Untersuchungen fanden an Böden des Langzeitexperimentes zur organischen und anorganischen Düngung in Askov statt. Unser analytischer Ansatz basierte auf einer Kombination der Extraktion von labilem P_o mittels makroporösem Anionenaustauscher‐Harz und der Kennzeichnung von Struktur und Herkunft des NaOH‐extrahierbaren P_o mittels ³¹P‐NMR‐Spektroskopie. Die Analysen wurden an der Feinerde und an Korngrößenfraktionen durchgeführt. Die Ergebnisse zeigen, dass Harz‐Extraktion einen aktiven Pool an P_o isoliert, welcher v.a. aus mikrobiell synthetisierten Strukturen besteht. Die Größe dieses Pools variiert im Jahresgang und hängt von der P‐Düngung ab. Die Art des Düngers (NPK gegenüber Stallmist und Gülle) scheint demgegenüber den labilen P_o kaum zu beeinflussen. Der größte Teil des leicht verfügbaren P_o ist in der Tonfraktion lokalisiert. Es ist daher zu schließen, dass diese Fraktion wichtig im kurzfristigen Umsatz von P_o ist.     

Location and chemical composition of stabilized organic carbon in topsoil and subsoil horizons of two acid forest soils

The ¹⁴C age of soil organic matter is known to increase with soil depth. Therefore, the aim of this study was to examine the stabilization of carbon compounds in the entire soil profile using particle size fractionation to distinguish SOM pools with different turnover rates. Samples were taken from a Dystric Cambisol and a Haplic Podzol under forest, which are representative soil types under humid climate conditions. The conceptual approach included the analyses of particle size fractions of all mineral soil horizons for elemental composition and chemical structure of the organic matter by ¹³C cross-polarization magic angle spinning nuclear magnetic resonance (CPMAS NMR) spectroscopy. The contribution of phenols and hydroxyalkanoic acids, which represent recalcitrant plant litter compounds, was analyzed after CuO oxidation.In the Dystric Cambisol, the highest carbon concentration as well as the highest percentage of total organic carbon are found in the <6.3 μm fractions of the B and C horizons. In the Haplic Podzol, carbon distribution among the particle size fractions of the Bh and Bvs horizons is influenced by the adsorption of dissolved organic matter. A relationship between the carbon enrichment in fractions <6.3 μm and the ¹⁴C activity of the bulk soil indicates that stabilization of SOM occurs in fine particle size fractions of both soils. ¹³C CPMAS NMR spectroscopy shows that a high concentration of alkyl carbon is present in the fine particle size fractions of the B horizons of the Dystric Cambisol. Decreasing contribution of O-alkyl and aromatic carbon with particle size as well as soil depth indicates that these compounds are not stabilized in the Dystric Cambisol. These results are in accordance with data obtained by wet chemical analyses showing that cutin/suberin-derived hydroxyalkanoic acids are preserved in the fine particle size fractions of the B horizons. The organic matter composition in particle size fractions of the top- and subsoil horizons of the Haplic Podzol shows that this soil is acting like a chromatographic system preserving insoluble alkyl carbon in the fine particle size fractions of the A horizon. Small molecules, most probably organic acids, dominate in the fine particle size fractions of the C horizons, where they are stabilized in clay-sized fractions most likely due to the interaction with the mineral phase. The characterization of lignin-derived phenols indicated, in accordance with the NMR measurements, that these compounds are not stabilized in the mineral soil horizons.     

Availability of nitrogen and phosphorus in forest soils in northeastern Tasmania

Summary Rates of N mineralization and of N uptake were measured in situ in three eucalypt forests and a cool-temperate rainforest, and were correlated with productivity. All of the soils had a high capacity for immobilization, and nitrification was insignificant. Changes in both organic and inorganic P fractions during in situ containment of soils were small. While the concentration of inorganic available P was not related to forest productivity, a measure of labile organic P was closely related both to productivity and to P in the microbial biomass. Estimates of inorganic- and organic-N availability were highly correlated with independent estimates of organic-P availability, and the results are discussed in relation to biological control of nutrient availability in the surface horizons of forest soils.     

基于31P NMR的自然成土过程中有机磷组分演变特征及影响因素研究进展

土壤有机磷(P_o)是土壤中重要的磷库,其形态、含量与生物有效性随成土过程而发生变化,进而影响土壤磷素供应、养分平衡及生态系统生产力。然而,与土壤无机磷(P_i)相比,以往的研究对P_o的重视不够,这主要是由于土壤中P_o的提取、分析和鉴定方法难于P_i。近年来,随着液相³¹P核磁共振(³¹P NMR)波谱技术在土壤学领域的应用,为定量分析土壤P_o组分及含量提供了新的技术手段,同时为更好地理解生态系统演化过程中不同形态P_o的转化特征奠定了基础。本文主要总结了土壤P_o的种类和性质,介绍了液相³¹P NMR分析土壤P_o的原理和方法,在此基础上综述了自然成土过程中不同形态P_o的转化特征及其影响因素,并指出了需进一步研究的方向和关键科学问题：包括量化成土过程中不同形态P_o转化速率、途径与环境阈值,阐明...