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1.
The taxonomic hierarchy and nationwide distribution of soils with a salic horizon were studied using the USA Natural Resources Conservation Service Soil Survey Geographic (SSURGO) Database to provide a more holistic view of the role of soil-forming factors in pedogenesis than from isolated case studies.Soils with a salic horizon occupied an area of 11 000 km2,i.e.,0.1% of land area in the contiguous USA.These soils occur narrowly in three great groups(Aquisalids,Haplosalids and Halaquepts),11 subgroups,and 97 soil series.Soils with a salic horizon commonly had a mesic (50% of soil series) or thermic (19%) soil-temperature class,an aquic (89%) soil-moisture class,a mixed mineral class (79%),a calcareous (52%)reaction class,a superactive (59%) cation exchange activity class,and a fine (24% of soil series),fine-loamy (24% of soil series),or fine-silty (19% of soil series) particle-size class.Soils with a salic horizon were concentrated in the Basin and Range Province of western USA.The key pedogenic processes leading to the development of salic horizons were salinization,gleization,and calcification,with some evidence for argilluviation and silicification.  相似文献   

2.
A dune area of 2 km2 in the Negev (Israel) with an annual precipitation of 90 mm was mapped. The soils developed from eolic and fluviatile sediments were Arenosols, Calcisols. Solonchaks, Regosols and Fluvisols. The Arenosols of the dunes are more homogeneous in texture and salt content than the soils of the interdunal corridors: Besides the Fluvisols, also the Calcisols, Solonchaks and Regosols are stratified due to episodic flooding by a wadi, and are rich in salts and lime. The soils are of minor development. Aggregation and enrichment of lime, enrichment and movement of salts, and the enrichment of organic substances are indications of soil formation. The distribution of salts within the profiles was calculated by their solubility. High and low soluble salts appear together in thin layers of Calcisols, Solonchaks and Fluvisols, while the most-soluble salts appear in deeper layers. The salts, therefore, must have accumulated by lateral movement, precipitation and temporal flooding. Influence of groundwater can therefore be excluded. The Arenosols also show the same sequence of salt types, indicating the accumulation due to precipitation and eolic mass movement. Abandoned arable land sites did not show any different soil characteristics from the unused soils. On the basis of the distribution of salts in the profiles and soil types genesis and classification of the soils is discussed.  相似文献   

3.
The morphology of humus profiles, developed on recent sandy coastal dune ecosystems, is studied on macro- and microscale. Humus and soil profiles were described, sampled and analysed. Undisturbed, oriented samples were taken from the surface horizons for micromorphological study. The soils are situated in the National Biological Reserve of the Opal Coast, Merlimont, France and near De Haan, Belgium. On both sites, the parent material consists of aeolian calcareous sand. Surface horizons, however, are decarbonated due to leaching processes.In Merlimont, the sequence consists of two profiles, one under Pinus nigra ssp. laricio and one under Populus nigra ssp. nigra, characterised by a Resimor1/Dysmoder, 2 and Rhizomull, 1/Mesomull , 2 humus type, respectively. At the De Haan site, three profiles under Quercus robur, Populus ssp. and P. nigra var. austriaca are investigated. The humus types are respectively Mullmoder, 1 to Mull/Dysmull , 2, Mull , 1/ Oligomull , 2, Mormoder , 1/Dysmoder , 2.Differences among the humus profiles are related to presence/absence among the L-, F-, H- and A-horizons, structure, rooting, presence of hyphae, sclerotia and excrements.Macromorphologically, the difference between humus profiles under coniferous and deciduous forest/grassland is evident by thicker L-, F and/or H-horizons under coniferous trees. The microstructure of the L- and F-horizons shows a loose packing of subhorizontally oriented needles. The microstructure of the H-horizons varies from intergrain microaggregate to locally weak crumb. The microstructure of the surface mineral horizon of all profiles is mainly intergrain microaggregate, sometimes single grain and exceptionally bridged grain. Intimate mixing and complexation of organic matter to the mineral fraction into aggregates is very limited in the A-horizons. All A-horizons, irrespective of the humus type, are to some degree characterised by a “pepper and salt” appearance. The horizon symbol “H+E” is introduced to label this morphology.The Mull humus forms under deciduous trees are indicative of rather intense mesofauna activities. The absence of a crumb structure in the A-horizon of these soils could be due to the fast disintegration of earthworm casts in these sandy soils with no clay or silt fraction.  相似文献   

4.
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5.
《CATENA》1998,32(1):23-35
Several studies have documented the severity of recent soil erosion on the Canadian prairies where cultivation started about a century ago. Little quantitative information is available on erosion before 1960. This study attempts to quantify post- and pre-1960 soil erosion in a small cultivated basin near Saskatoon, Saskatchewan, Canada, by measuring 137Cs and magnetic susceptibility (χ) distribution with depth. Soil cores were collected along six transects (three across closed depressions and three across the drainage channel) in the cultivated field, and one transect across an uncultivated depression. The cores were sliced into 3-cm layers and the soil analyzed for 137Cs, χ, and organic and inorganic C. High variability in χ with depth in eroding areas (as indicated by 137Cs) made it impossible to use χ to quantify past soil losses in these locations. However, these eroding upper and middle slope positions have a much higher χ than lower slope areas where soil deposition occurs and where the variability in χ with depth could be used to estimate soil deposition. Estimating soil deposition from the χ vs. depth profiles was more successful in the closed depressions than in the drainage channel, where the χ profiles may reflect the variable source areas of the materials rather than the pedological conditions. The data indicated that soil deposition since 1960 has been about 30 to 50% of that prior to 1960. This suggests that soil deposition rates, and by implication, soil erosion rates, have been relatively steady since cultivation of these soils started, although there are clear indications that the spatial pattern of deposition has varied.  相似文献   

6.
《Soil & Tillage Research》1988,12(3):285-298
The objective of this study was to evaluate quantitatively the magnitude of the spatial and temporal variation for 7 soil physical properties on a conventionally-tilled Nigerian Paleustult. A 0.4-ha plot was disc-ploughed, disc-harrowed twice, subjected to tractor-wheel traffic at regular space intervals and then seeded to maize (Zea mays, L.). There were significant differences in the physical properties owing to tillage position (spatial variability) and date of sampling (temporal variability), more so in the 0–10-cm layer than in the 10–20-cm layer. In the surface layer, bulk density (Db) and penetrometer resistance (PR) were significantly higher (P ⩽ 0.01) along the tyre marks (maximum Db = 1.76 Mg m−3) than in the uncompacted crop row (maximum Db = 1.35 Mg m−3) and interrow positions (maximum Db = 1.46 Mg m−3). Saturated hydraulic conductivity (Ksat), total porosity (TP) and macroporosity (M) were significantly lower along the tyre mark than in the crop row and interrow positions. Ksat ranged from 0.6 to 42.8 cm h−1, TP, from 0.34 to 0.50 cm3 cm−3 and M from 0.06 to 0.25 cm3 cm−3 along the tyre mark and crop row positions, respectively. Significant temporal changes were noticed only in Ksat, soil moisture content (MC) and PR. Ksat increased steadily with time along the tyre mark, but showed an irregular trend in the other two positions. PR did not change with time along the tyre marks but it increased significantly with time along the other two positions. MC changed according to the periodicity of rainfall. Only TP varied, owing to tillage position × date interaction. The 10–20-cm layer was spatially less variable but temporally more viarable than the surface layer. Only Ksat and PR showed significant changes owing to the tillage positions, but Db, Ksat, PR and moisture retained at 10 kPa suction (τv10) showed significant temporal changes. Only τv110 varied owing to position × date interaction in this layer.  相似文献   

7.
Various parameters of the soil microbial community may be used in soil quality evaluation and environmental risk assessment. The objectives of this study were to assess the effects of different environmental factors on the characteristics of forest humus microbial communities, and to test which environmental factors most affect the gross microbial indices and physiological profiles of these communities. Samples were taken at 71 plots located in a heavily polluted area of the Krakowsko-Cze¸stochowska upland in southern Poland. The samples were analyzed for pH in KCl (pHKCl), organic C (Corg), total N (Nt) and S (St), and for total and soluble Zn, Pb and Cd concentrations. The considered microbial parameters included basal respiration (BAS), microbial biomass (Cmic), Cmic-to-Corg ratio, and community-level physiological profiles (CLPPs) studied using BIOLOG® Ecoplates. Multiple regression analysis was used to estimate the effects of humus properties on the microbial parameters. It indicated that St and Corg-to-Nt ratio were the most important factors positively affecting Cmic (β=0.15 and 0.11, respectively) and BAS (β=0.13 and 0.08, respectively). The Cmic-to-Corg ratio was related positively to St (β=0.12) but negatively to Nt (β=−0.08). The effects of pHKCl and heavy metals on the gross microbial indices were significant but less important. The most important effect on microbial activity on BIOLOG® plates and CLPPs was from pHKCl. The other significant variables included St, Corg-to-Nt and interactions of heavy metals with pHKCl. It was concluded that Cmic, Cmic-to-Corg and BAS might be good indicators of the general status of soil microbial communities, but their use in studying heavy metal effects may entail difficulties in separating the effects of other factors. The sensitivity of the BIOLOG® test to pHKCl suggests that it may be useful for studying the effects of acidification or liming on soil microbial communities. The significant effect of the interactions between heavy metals and other variables on physiological profiles indicated that high heavy metal content affects the metabolic functions of soil microbial populations.  相似文献   

8.
科尔沁沙地半固定沙丘不同坡位土壤C,N特征   总被引：1，自引：0，他引：1  
[目的]研究沙丘不同坡位土壤碳氮的分布特征,旨在探索沙丘不同坡位植被演替机制。[方法]选取高于5m的半固定沙丘,沿主要风向于坡底、坡中、坡顶和背风坡设置样点,对土壤容重、土壤总有机碳含量和土壤总氮含量进行测定,并计算碳氮比、碳氮密度和碳氮储量。[结果](1)不同坡位土壤碳含量均随深度增加显著降低,主要变异层发生在0—40cm层。不同坡位土壤碳含量在30—40cm层和60—100cm层存在差异。(2)氮含量与容重在不同坡位和不同深度均不存在显著差异性,碳氮比在坡底和坡顶存在显著的垂直差异性,背风坡60—100cm层土壤碳氮比显著高于其它坡位。(3)各坡位土壤碳密度随深度增加显著下降。30—40cm层土壤碳密度存在显著的坡位差异,而土壤氮密度的垂直差异和坡位间差异均不显著。(4)半固定沙丘土壤碳氮储量分别为716.89和94.14kg/m2,不同坡位差异性不显著;碳储量的构成在4种坡位差异较大,而各坡位不同深度土壤氮储量对总储量的贡献差异较小。[结论]科尔沁沙地半固定沙丘土壤碳氮含量与密度不同坡位的差异较小,同时各坡位的碳氮均存在显著的垂直差异性,尤其在30—40cm层,变异程度较大,这可能与该层植物根系分布有关。  相似文献   

9.
Mercury deposition was monitored at two mountain sites in Quebec using transplanted lichens and moss. The terricolous lichen species Cladina rangiferina, the epiphytic lichen species Hypogymnia physodes, and the feather moss Pleurozium schreberi were transplanted from a northern Ontario boreal site to the bases and summits of Roundtop Mountain and Mt. Tremblant in southern Quebec. After 12 months, transplants of C. rangiferina sited at the base and summit of Roundtop mountain and the summit of Mt. Tremblant showed a significant increase in mercury concentration over controls (p < 0.05). The largest difference occurred at the summit of Roundtop mountain where mercury concentration was 81.4 ± 10.9 ppb as compared to 45.6 + 10.6 ppb at the control site. No significant increases in mercury concentration in P. schreberi were seen after 12 months at any site althought trends of increase were apparent. After 20 months, further significant increases in Hg content were observed in both the terricolous lichen and the feather moss at both the Roundtop Mountain base and summit sites. A significant increase in Hg content of P. schreberi was also noted at the Mt. Tremblant summit site. Over the length of the study the greatest mercury concentration increases were observed in the feather moss at the Roundtop Mountain summit site (with a 248.3 ± 30.0 ppb mercury concentration as compared to 108.3 ± 30.0 ppb in controls). No significant change in mercury concentration in the epiphyte H. physodes was found during the study. These data indicate that mercury deposition is occurring, especially to higher elevation sites. While mercury inputs at the summits may be increased by the effects of fog, increases in mercury at the base sites cannot be accounted for the same way, but may represent the importance of dry deposition processes.  相似文献   

10.
科尔沁不同沙地土壤饱和导水率比较研究   总被引：14，自引：0，他引：14  
用Guelph入渗仪对科尔沁沙地不同沙漠化阶段土壤不同层次的土壤饱和导水率(Kfs)进行测定,分析研究了Kfs与沙地类型、土层厚度、沙丘坡位及土壤理化性质的关系.结果表明:(1)草地(潜在沙漠化)、固定沙丘(轻度沙漠化)和流动沙丘(严重沙漠化)的Kfs依次增大,平均值分别为2.15、4.79和5.89 mm min-1,呈现出土壤入渗能力随沙漠化程度的增强而增强的趋势;三种沙地间Kfs差异显著,沙丘不同坡位Kfs也有较大差异,表明科尔沁沙地Kfs具有较高的空间异质性;(2)三种沙地Kfs随深度的变化规律差异较大,草地Kfs随深度呈抛物线状变化,而固定沙丘Kfs随深度呈指数函数变化;(3)通过逐步回归分析发现对Kfs影响较大的土壤理化性质是土壤有机质含量、土壤细砂含量、黏粉粒含量和粗砂粒含量,并且Kfs与前三个因素呈显著的负相关关系,与最后一个因素呈显著的正相关关系.  相似文献   

11.
This work focuses on the behaviour of mercury in lateritic soil profiles found in the Serra do Navio and Tartarugalzinhoareas of the State of Amapá in Northern Brazil. The Hg contents are high in the upper horizons of the soil profiles(100–300 μg kg-1), and decrease to less than 100 μg kg-1 at depths of 200 or 300 cm. The higher levels of Hg are associated with higher Fe concentrations, particularly in the ferruginous accumulations as mottles andnodules. For each horizon of the soil profile, balance calculations were used to distinguish the amount of mercury naturally accumulated from rocks through lateritic pedogenesis (lithogenic mercury) from the anthropogenic mercury introduced in the profile through atmospheric contamination. The results show that the anthropogenic contribution is significant in the upper horizons (up to 95%% of the total Hg), and decreases downward in the soil profile. Mercury burdens were calculated for soil profiles in both upslope (272 880 and 217 440 μg m-2 for the first 70 cm) and downslope positions (118 800 and 182 160 %μg m-2 for the first 70 cm). The loss of Hg in downslope profiles seems to be related to the natural evolution of iron duricrust into latossols, which has been brought about by climatic changes toward increasing humidityin the Amazon since the Tertiary.  相似文献   

12.
The southeastern Tibetan Plateau, which profoundly affects East Asia by helping to maintain the stability of climate systems, biological diversity and clean water, is one of the regions most vulnerable to water erosion, wind erosion, tillage erosion, freeze–thaw erosion and overgrazing under global climate changes and intensive human activities. Spatial variations in soil erosion in terraced farmland (TL), sloping farmland (SL) and grassland (GL) were determined by the 137Cs tracing method and compared with spatial variations in soil organic carbon (SOC) and total nitrogen (total N). The 137Cs concentration in the GL was higher in the 0–0.03 m soil layer than in the other soil layers due to weak migration and diffusion under low precipitation and temperature conditions, while the 137Cs concentration in the soil layer of the SL was generally uniform in the 0–0.18 m soil layer due to tillage-induced mixing. Low 137Cs inventories appeared at the summit and toe slope positions in the SL due to soil loss by tillage erosion and water erosion, respectively, while the highest 137Cs inventories appeared at the middle slope positions due to soil accumulation under relatively flat landform conditions. In the GL, the 137Cs data showed that higher soil erosion rates appeared at the summit due to freeze–thaw erosion and steep slope gradients and at the toe slope position due to wind erosion, gully erosion, freeze–thaw erosion and overgrazing. The 137Cs inventory generally increased from upper to lower slope positions within each terrace (except the lowest terrace). The 137Cs data along the terrace toposequence showed abrupt changes in soil erosion rates between the lower part of the upper terrace and the upper part of the immediate terrace over a short distance and net deposition on the lower and toe terraces. Hence, tillage erosion played an important role in the soil loss at the summit slope positions of each terrace, while water erosion dominantly transported soil from the upper terrace to the lower terrace and resulted in net soil deposition on the flat lower terrace. The SOC inventories showed similar spatial patterns to the 137Cs inventories in the SL, TL and GL, and significant correlations were found between the SOC and 137Cs inventories in these slope landscapes. The total N inventories showed similar spatial patterns to the inventories of 137Cs and SOC, and significant correlations were also found between the total N and 137Cs inventories in the SL, TL and GL. Therefore, 137Cs can successfully be used for tracing soil, SOC and total N dynamics within slope landscapes in the southeastern Tibetan Plateau.  相似文献   

13.
Soil organic carbon (SOC) in eroded soil can be redistributed from upper slope positions and deposited and sequestered in depressional areas. However, the SOC lost from soil erosion is normally not considered when soil carbon budgets are derived and this could result in an overestimation of SOC loss from the agricultural areas. The impact of soil redistribution on the SOC budget of a sloping landscape in the Black soil region in Northeast China was studied using the presence of the 137Cs tracer which has been deposited since 1954 and the fly‐ash tracer, which was deposited in 1903. Five landscape positions (summit, shoulder‐, back‐, foot‐ and toe‐slope) were selected and included in this study. The depths of 137Cs and fly ash and the SOC content of the deposition layers were used to calculate the change in C content of the soil in the various landscape positions over the last century. We found that the most severe soil erosion occurred in soils in the shoulder‐slope position followed by the back‐slope and the summit positions. Soil deposition occurred in the toe‐slope position followed by the foot‐slope position. A total of 683 kg C was eroded from the summit, shoulder‐ and back‐slopes (in a 1 m wide strip) over the past 100 years and 418 kg C (about 61·2 per cent) was deposited in the low‐lying areas (foot‐ and toe‐slopes). Over half (61·5 per cent) of the deposition (257 kg SOC) occurred over the past 50 years. Most of the previously reported loss of C from the upper slope positions in the Black soils was in fact sequestered in the deposition areas in the landscape. Copyright © 2005 John Wiley & Sons, Ltd.  相似文献   

14.
Spatial variation is a ubiquitous feature of natural ecosystems, especially in arid regions, and is often present at various scales in these regions. To determine the scale dependence of the heterogeneity of soil chemical properties and the dominant scales （factors） for soil heterogeneity in arid regions, the spatial variability of soil resources was investigated in the Gurbantunggut Desert of Central Asia at the scales of 10-3, 10-2, 10-1, 100, 101, 102, 103 and 104 m （from individual plant to population or community to ecosystem）. Soil chemical properties including pH, electrical conductivity （EC）, organic carbon, total nitrogen, available nitrogen, total phosphorus, and available phosphorus were considered in the investigation. At a scale of 10-1 m, which represented the scale of individual plant, significant enrichment of soil resources occurred under shrub canopy and ＂fertile islands＂ formed in the desert ecosystem. Soil EC exhibited the largest heterogeneity at this scale, indicating that individual plants exerted a great influence on soil salinity/alkalinity. Soil nutrients exhibited the greatest heterogeneity at a scale of 102 m, which represented the scale of sand dune/interdune lowlands （between communities）. The main important factors contributing to soil spatial heterogeneity in the Gurbantunggut Desert were individual plants and different topographic characteristics, namely, the appearance of vegetation, especially shrubs or small trees, and existing sand dunes. Soil salinity/alkalinity and soil nutrient status behaved differently in spatial heterogeneity, with an inverse distribution between them at the individual scale.  相似文献   

15.
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16.
To evaluate the potential for constructed wetlands to treat acid coal mine drainage, six model wetland mesocosms (each 2.4 m × 15 cm) were filled with Sphagnum peat (15 cm deep), planted either with cattails (Typha latifolia) and living Sphagnum, living Sphagnum only, or left as bare peat (2 mesocosms per treatment). The model wetlands were exposed to synthetic acid coal mine drainage (pH 3.5, concentrations of Fe2+, Al3+, Mn2*, Ca2+, and Mg2+ of 78.8, 10.0, 5.2, 12.0, and 4.5 mg L?1, respectively) at a rate of 90 mL min?1, 6 hr d?1, 5 d wk?1, over a 16 week period. Chemical analysis of peat at periodic intervals indicated that the model wetlands were net sources of Al3+, Mn2+ Ca2+ and Mg2+, but net sinks for Fe2+. Type of vegetation had no significant effect on Fe2+ retention; of the 204 g of Fe2+ added to the model wetland systems, 162 g were retained. Formation of Fe oxides accounted for 73 to 86% of the Fee' retention, with exchangeable Fe contributing 0.2 to 1.2%, organically bound Fe contributing 4 to 19%, and residual Fe contributing 7 to 15% of total Fee' retention. Fe retention was greatest at the inflow ends of the model wetlands where Fe retention appeared to reach saturation at a final Fe concentration in the peat of 235 mg g?1. At the rate of application of the synthetic acid mine drainage, we estimated that the model wetland systems would have reached complete Fe saturation after 157 days. We suggest that the mesocosm approach could be useful in generating site-specific data that can be applied to the formulation of cost-benefit analyses that can compare a proposed wetland treatment system with alternative conventional chemical methods for treating acid mine drainage.  相似文献   

17.
In order to evaluate the variability of the soil profiles at two shapes (concave and convex) and five positions (summit, shoulder, back slope, footslope and toeslope) of a slope, a study of a virgin area was made in a Beech stand of mountain forests, northern Iran. Across the slope positions, the soil profiles demonstrated significant changes due to topography for two shape slopes. The solum depth of the convex slope was higher than the concave one in all five positions, and it decreased from the summit to shoulder and increased from the mid to lower slope positions for both convex and concave slopes. The thin solum at the upper positions and concave slope demonstrated that pedogenetic development is least at upper slope positions and concave slope where leaching and biomass productivity are less than at lower slopes and concave slope. A large decrease in the thickness of O and A horizons from the summit to back slope was noted for both concave and convex slopes, but it increased from back slope toward down slope for both of them. The average thickness of B horizons increased from summit to down slopes in the case of the concave slope, but in the case of convex slope it decreased from summit to shoulder and afterwards it increased to the down slope. The thicknesses of the different horizons varied in part in the different positions and shape slopes because they had different plant species cover and soil features, which were related to topography.  相似文献   

18.
To investigate the consequences of long-term N additions on soil CH4 dynamics, we measured in situ CH4 uptake rates, soil profiles and kinetics parameters during the growing season in a temperate deciduous forest in northwestern Pennsylvania (Allegheny College Bousson Environmental Forest). Measurements were made in control and adjacent plots amended with 100 kg N ha–1 year–1 for 8 years. We found that the in situ consumption rates were 0.19±0.02 (mean±SE) for the control and 0.12±0.01 mg CH4–C m–2 h–1 for the N treatment, indicating that consumption had been reduced by 35% after 8 years of N amendments. Despite the large difference in rates of consumption, there were no differences in the CH4 concentration profiles between the control and N-amended plots. Laboratory incubations of CH4 consumption throughout the soil column (organic horizon and mineral soil depths) showed that rates were greatest in the organic horizon of both control and N-amended soils, although consumption was reduced by 42% in the N-amended plot. However, the rate in the organic horizon was only about 50% the rate measured in organic horizons at other temperate forests. The apparent Km [Km(app)] value in the organic horizon of the control plot was fourfold less than the Km(app) value in the organic horizon of another temperate forest, but similar to the Km(app) values in adjacent plots amended with N for a decade. Unlike results for other temperate forests, Km(app) values at Bousson generally did not decrease with soil depth. These results indicate that N cycling strongly controls the CH4-consuming community, and suggest that alterations of the N cycle due to N deposition or addition may alter rates and the location of CH4 consumption by soils, even in soils with high N content and cycling rates.  相似文献   

19.
Distribution of actinomyeetes in beach and dune sand at two sites was studied. At one site. dunes were eroding while at the other accretion of sand and dune development occurred. Actinomycetes occurred in low numbers in beach sand hul increased sharply when dunes were colonized by Ammophila arenaria (L) Link or Agropyron junceiforme (A & D Löve) A & D Löve. Micromonospora strains predominated in beach sand but Streptomyces was the predominant genus in dunes.Salinity tolerance of isolates was not clearly related to their source but tolerance of dune isolates was generally greater than those from the beach. Tolerance of Streptomyces strains varied but all Micromonospora isolates were intolerant of salinities above that of sea water.Evidence for increased growth of actinomycetes in the root region of A. arenaria and A. junceiforme was obtained but there was little qualitative difference between those in the root region and root-free sand. In laboratory experiments actinomycetes colonized old. dead Ammophila roots more readily than young ones and arose carly in succession on the former. Young, living roots stimulated bacteria and fungi but not actinomyeetcs. It was concluded that most activity of actinomycetes in the Ammophila root region occurred on old root tissue and it was suggested that this might be true of other plants.  相似文献   

20.
Andosols often accumulate soil organic matter (SOM) in large amounts. To investigate the factors controlling the stability and lability of organic carbon (OC) in humus horizons of Andosols, we selected 19 A horizon samples (surface and subsurface horizons) from the Field Station of Tohoku University including areas where benchmark soil profiles of non-allophanic Andosols are distributed. We determined the soil properties possibly controlling the OC accumulation, such as pH(H2O), 1 M KCl-extractable aluminum (KCl-Al), pyrophosphate-extractable Al and iron (Alp, Fep), acid oxalate-extractable silicon (Sio), total OC, water-extractable OC, and humified OC. To evaluate the OC mineralization, we measured the soil respiration rates in a laboratory for non-treated, neutralized (CaCO3, Ca(OH)2 and NaOH), and nutrient applied (KH2PO4, (NH4)2SO4) soil samples. Statistical analyses, including a path analysis, showed that the Alp and pH(H2O) values are directly related to the OC concentration (P?<?0.01 and P?<?0.05, respectively). There was a significant negative correlation (P?<?0.01) between the soil respiration rates of the non-treated samples and the ratios of the humified OC to total OC, showing that the humification of the SOM was definitely related to the OC stability. Effects of the chemical treatments to the soil respiration rates were greater in the surface horizon samples with an abundant labile OC than those in the subsurface samples. Neutralization affected the soil respiration rates more significantly than the nutrient application. Among the neutralization treatments, the liming materials more effectively increased the respiration rates. This was probably due to an increase in the lability of the humified OC by liming.  相似文献   

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