摘要:

SummaryThe soil is important in sequestering atmospheric CO2and in emitting trace gases (e.g. CO2, CH4and N2O) that are radiatively active and enhance the ‘greenhouse’ effect. Land use changes and predicted global warming, through their effects on net primary productivity, the plant community and soil conditions, may have important effects on the size of the organic matter pool in the soil and directly affect the atmospheric concentration of these trace gases.A discrepancy of approximately 350 × 1015g (or Pg) of C in two recent estimates of soil carbon reserves worldwide is evaluated using the geo‐referenced database developed for the World Inventory of Soil Emission Potentials (WISE) project. This database holds 4353 soil profiles distributed globally which are considered to represent the soil units shown on a1/2° latitude by1/2° longitude version of the corrected and digitized 1:5 M FAO–UNESCO Soil Map of the World.Total soil carbon pools for the entire land area of the world, excluding carbon held in the litter layer and charcoal, amounts to 2157–2293 Pg of C in the upper 100 cm. Soil organic carbon is estimated to be 684–724 Pg of C in the upper 30 cm, 1462–1548 Pg of C in the upper 100 cm, and 2376–2456 Pg of C in the upper 200 cm. Although deforestation, changes in land use and predicted climate change can alter the amount of organic carbon held in the superficial soil layers rapidly, this is less so for the soil carbonate carbon. An estimated 695–748 Pg of carbonate‐C is held in the upper 100 cm of the world's soils. Mean C: N ratios of soil organic matter range from 9.9 for arid Yermosols to 25.8 for Histosols. Global amounts of soil nitrogen are estimated to be 133–140 Pg of N for the upper 100 cm. Possible changes in soil organic carbon and nitrogen dynamics caused by increased concentrations of atmospheric CO2and the predicted associated rise in t

ISSN:1351-0754    

DOI:10.1111/j.1365-2389.1996.tb01386.x

出版商:Blackwell Publishing Ltd    

年代:1996

数据来源: WILEY

摘要:

SummaryThe mineralogies of ‘Tirs’ (Typic Pelloxererts), and ‘Debs’ (Typic Haploxerolls and Typic Xerochrepts) soils of the Gharb plain in north‐western Morocco are investigated, with special attention given to the determination of the nature of the smectitic phase using the lithium test (Li test) and the alkylammonium method. The sand and silt mineralogy of Tirs soils is dominated by quartz with small amounts of feldspars and kaolinite. The sand and silt fractions of Dehs soils also contain significant amounts of mica, chlorite, and interstratified phyllosilicates. The clay minerals of Tirs soils are predominantly a high‐charge smectite. The estimated interlayer charge for this phase is 0.61 mol(c)/O10(OH)2and the fraction of tetrahedral charge varies from 38 to 44%. Although the percentage tetrahedral charge is less than 50%, the smectitic phase behaves as beidellite with the Li test. Dehs clays are more heterogeneous, consisting of smectite, vermiculite, illite, kaolinite, chlorite, and interstratified illite/smectite and illite/vermiculite. The Li test and the alkylammonium method demonstrate that a high‐charge smectite or vermiculite is interstratified with illite. A low‐charge montmorillonite is also present both in Tirs and in Dehs soils. The high‐charge beidellitic phase is believed to be a transformation product of mica, whilst the low charge montmorillonite is thought to be inherited from th

ISSN:1351-0754    

DOI:10.1111/j.1365-2389.1996.tb01387.x

出版商:Blackwell Publishing Ltd    

年代:1996

数据来源: WILEY

摘要:

SummaryTemperate saltmarshes are a potential source of atmospheric methane. We have measured the concentration and emission of methane in typical saltmarsh soils (Salic Fluvisols) and humus‐rich saltmarsh soils (Thionic Fluvisols) from the German North Sea coast. We also measured the methane production rates of the latter. The methane content of typical saltmarsh soils reached 12.0 μmol 1−1, although values of 1–4 μmol 1−1were usual. The sulphate concentrations of the pore‐water were about 10 mm, which means sulphate reduction is not limited and methanogenesis would be suppressed. Methane concentrations were generally largest in summer. Independent of the redox potential and the degree of soil development, methane concentrations were smallest in those soils poorest in humus. Methane emission rates were almost zero. In the humus‐rich saltmarsh soils, methane concentrations were roughly a thousand times larger than those in typical saltmarsh soils, reaching values of 23 mmol 1−1The sulphate concentrations of the pore‐water were often less than 1 mM, indicating limited sulphate reduction. Methane production was up to 80 μg cm−3day−1and was not inhibited when we added sulphate. Methane emission rates reached up to 190 μg m−2day−1in summer, with values up to 20 μg m−2day−1at other times. The two kinds of saltmarsh soil behave quite differently: the typical saltmarsh soils act as a sink for methane; the humus

ISSN:1351-0754    

DOI:10.1111/j.1365-2389.1996.tb01388.x

出版商:Blackwell Publishing Ltd    

年代:1996

数据来源: WILEY

摘要:

SummaryThe analysis of free lipids in 12 soils from three representative types of Mediterranean forest has been carried out in an attempt to describe diagnostic molecules reflecting differences between the ecosystems and the intensity of the soil organic matter turnover. The study centred on the analysis by gas chromatography–mass spectrometry of the soil compounds extracted with petroleum ether from soils in central Spain, developed under monospecific formations of stone pine (Pinus pined), evergreen oak (Quercus rotundifolia) and Spanish juniper (Juniperus thurifera), the lipid extracts from their leaves also being analysed as reference material.The comparison between the distribution patterns of alkanes and fatty acids in plant lipids and the corresponding soil lipids was used to assess the extent to which the former accumulate in soil or are substituted by other biogenic or diagenetic homologues. In general, the alkane patterns showed the greatest variation in soils under oak, and the differences between lipid patterns in plant and soil were greatest in the juniper forests. As indicators of the vegetation type, the soil fatty acids had little value.Up to 60 major cyclic compounds were identified, including mainly di‐ and sesquiterpenes, in addition to some monoterpenes and nonterpenic naphthalenes and decalins. Of these major constituents, 33 compounds were found in soil but were not present in plant extracts, and 18 compounds were identified in plants but were not in the soils. The results suggest an arrangement of the soil samples based on the composition of the signature lipid assembla

ISSN:1351-0754    

DOI:10.1111/j.1365-2389.1996.tb01389.x

出版商:Blackwell Publishing Ltd    

年代:1996

数据来源: WILEY

摘要:

SummaryThe green fraction of humic acids (HAs), Pg, was fractionated by gel chromatography on Sephadex G‐50. Repeated chromatography of the crude Pg obtained by the first chromatography of HA yielded a sharp peak (G1) and two broad bands (G2) of purified Pg. The recovery of Pg in G1and G2as percentages of the total Pg content of the HA were 16.2 and 14.5%, respectively. Distinct peaks were detected at 615, 570, 450 and 280 nm in the UV‐visible spectra of both G1and G2in alkali solutions. Estimates of weight‐average molecular weight were 9.7 * 103for G1and 1.23 * 104for G2. In the1H‐NMR spectra the percentage of hydroxyl groups of 4,9‐dihydroxy‐perylene‐3, 10‐quinone (DHPQ) nuclei, which are known to be the chromophore of Pg, was 4.1 and 4.5% of the total H, respectively. Based on these values and the H/C ratios, DHPQ‐C was estimated as 28% of total C.13C‐NMR spectra obtained using inverse‐gated decoupling yielded 40–41% aromatic C, which suggested the presence of aromatic rings other than DHPQ. All of the IR,13C‐ and1H‐NMR spectra indicated that the two purified Pg samples largely differed from each other in their contents of alkyl an

ISSN:1351-0754    

DOI:10.1111/j.1365-2389.1996.tb01390.x

出版商:Blackwell Publishing Ltd    

年代:1996

数据来源: WILEY

摘要:

SummaryHumic substances contain significant quantities of free radicals which have important functions in many biological processes in soil involving electron transfer. Such radicals may be detected by electron spin resonance spectroscopy in both solid and solution state and are usually reported as giving a single unstructured peak. Humic acids from a range of soil types varying in parent material and pH have been examined by electron spin resonance spectroscopy of their solutions in 0.1mKOH. Spectra with an effective g‐value typical of an organic free radical were obtained. Observation of hyperfine structure was highly dependent on the instrument settings used. It was present at a modulation amplitude of 0.0142 mT, but not at 0.101 mT. Similarly, there was a reduction in resolution as microwave power was increased from 0.505–20 mW. This may explain the inability of some investigators to observe structure in soil humic acids. Resolution of hyperfine features was greatly enhanced by recording spectra in the second derivative mode. Using appropriate instrument settings all the humic acids showed hyperfine structure, although the intensity of these components varied by a factor of 100, being much greater in humic acid from highly acidic so

ISSN:1351-0754    

DOI:10.1111/j.1365-2389.1996.tb01391.x

出版商:Blackwell Publishing Ltd    

年代:1996

数据来源: WILEY

摘要:

SummaryA combination of radiocarbon (14C) dating and biomarker analyses of the aliphatic hydrocarbons in soil lipids is proposed as a novel and improved method for studying the environmental history of peaty soils. The radiocarbon concentration of unfractionated bulk organic matter, hydrolysed soil residues and two lipid fractions (the aliphatic hydrocarbons and carboxylic acids) recovered from a stagnohumic gley soil, were compared using AMS (accelerator mass spectrometry) and radiometric14C dating techniques. The radiocarbon ages recorded by the aliphatic hydrocarbon fractions were consistently older than those measured from the unfractionated soil, and were in most cases older than the residues remaining after acid hydrolysis. This pattern was observed at three different depths in the soil profile. The apparent age difference between the hydrocarbon fraction and its unfractionated substrate increased with depth. An abundance of long–chain n–alkanes, similar to those found in higher plant waxes, characterized the aliphatic hydrocarbon fraction from the deepest soil (at 21.5–24.5–cm depth). The radiocarbon age of this basal organic component (13470± 170 yearsbp) indicated that it derived from the initial re–establishment of vegetation on the local deglaciated landscape with the onset of the Windermere Interstadial (c. 14000–1300014C yearsbp). Bulk organic detritus within the basal horizon dated at some 3000 years younger, and presumably as a result of the downward penetration and retention of some mobile organic residues produced later in the development of the soil profile. The survival and apparent stratigraphical stability of these recoverable aliphatic hydrocarbons provides the opportunity, via the development of AMS dating, to measure an unambiguous radiocarbon age for the origin of organic residues retained in soils a

ISSN:1351-0754    

DOI:10.1111/j.1365-2389.1996.tb01392.x

出版商:Blackwell Publishing Ltd    

年代:1996

数据来源: WILEY

摘要:

SummaryThe basic principles of the electrophoretic behaviour of humic substances (HS) still need to be systematically investigated. HS extracted from a Cryorthod (HS–1) and from an Haplumbrept (HS–2) were first fractionated by ultrafiltration to obtain two series of fractions of reduced polydispersity with a nominal mean relative molecular mass (M) of 7500, 20000, 40000, 75000 and 200 000 Da. Fractions extracted from the same soil behaved like an homologous series when tested by size exclusion chromatography, showing a linear relation ofMwith molecular size. When plotted against their meanM, the elution volumes of HS fractions extracted from the two different soils originated lines of different slope. Absolute electrophoretic mobilities of the fractions were determined in polyacrylamide gel slabs of increasing polyacrylamide concentration using a single buffer system; in all gels there was a close linear relation between the electrophoretic mobility and the logarithm of the meanMof HS fractions. Extrapolation of mobilities of HS–1 at zero gel concentration gave intercepts that did not differ significantly, showing that there was a constant mobility for all fractions in free solution. These results mean that charge differences have little effect on the electrophoretic mobilities of HS extracted from the same soil and imply the theoretical possibility of determiningMdistributions of HS by polyacrylamide gel electrophoresis in a single buffer system. Mobilities of HS–2 fractions were compared with those of HS–1: the latter fitted the regression equations of mobility against logarithm of the molecular weight obtained from HS–1 humic substances only in gels of small acrylamide concentration. Deviations were larger at smallM, probably because of the increasing fulvic character of the fractions, and increased in gels of greater acrylamide concentration, indicating that charge differences may not be negligible when comparing humic substances extracted from diff

ISSN:1351-0754    

DOI:10.1111/j.1365-2389.1996.tb01393.x

出版商:Blackwell Publishing Ltd    

年代:1996

数据来源: WILEY

摘要:

SummaryThe effect of pH and the addition of carboxylates (acetate, oxalate, tartrate, salicylate and citrate) on the solubility of soil phosphate has been investigated to assess the possible effects of root exudates on phosphate availability. The soil was a neutral calcic Luvisol with a large pH buffer capacity. Various concentrations of strong acid (0–20 mmol kg−1) and anion (0–2 mmol kg−1) were applied to soil in suspension (0.5 g soil cm−3). The effect of 2 mmol kg−1oxalate on the adsorption isotherm of phosphate was also studied. The rate of isotopic exchange was largely unchanged by any of the treatments. Neither pH nor acetate had an effect on phosphate solubility. The addition of di– and trivalent anions increased phosphate solubility somewhat. The effect increased with increasing concentration of anion, and was generally independent of pH and the proportion of anion adsorbed. Oxalate was more efficient in limiting the adsorption of freshly added phosphate than in desorbing native phosphate. The results illustrate that rhizosphere acidification does not necessarily increase phosphate solubility. However, carboxylates, the conjugate bases of organic acids, may play an important role in improving the availability of s

ISSN:1351-0754    

DOI:10.1111/j.1365-2389.1996.tb01394.x

出版商:Blackwell Publishing Ltd    

年代:1996

数据来源: WILEY

摘要:

SummaryWe studied the sorption of phosphate and oxalate on a synthetic aluminium hydroxysulphate complex and the associated release of sulphate from this complex. In the pH range 4.0–9.0 the presence of phosphate or oxalate tended to increase the release of sulphate. Much more phosphate than oxalate was sorbed, but in most cases oxalate caused more removal of sulphate than did phosphate. Only in acid systems may these results be partly attributed to the greater solubilization of the complex in the presence of oxalate than in the presence of phosphate. At pH>8.0 in the presence of phosphate, and at pH>6.5 in the presence of oxalate, the quantities of sulphate replaced were greater than the quantities of phosphate or oxalate sorbed, suggesting that hydroxyl ions competed with phosphate and oxalate for sorption sites and sulphate removal. Sulphate was only partly removed from the complex even after repeated washings with phosphate or oxalate solutions or after 120 h in the presence of these ligands at pH 6.0. When phosphate and oxalate were added as a mixture much more phosphate than oxalate was retained. Phosphate strongly inhibited oxalate sorption, whereas oxalate partly prevented phosphate sorption only at pH<7.0. More sulphate was removed in the presence of both the anions than in the presence of phosphate alone, but less than that desorbed in the presence of oxalate alon

ISSN:1351-0754    

DOI:10.1111/j.1365-2389.1996.tb01395.x

出版商:Blackwell Publishing Ltd    

年代:1996

数据来源: WILEY