Hydromorphic and clay-related processes in soils from the Llanos de Moxos (northern Bolivia)

The Llanos de Moxos is one of the largest wetlands in the world (more than 100,000 km²) due to seasonal floods. The soil parent materials are fine Quaternary sediments brought by tributaries of the Amazon River. Forests cover some areas, although the dominant vegetation is a pastured savannah and backswamps. At present, the main land use is a very extensive rangeland, and slash and burn agriculture in minor areas.We have studied 15 profiles from several sample areas between Trinidad and San Ignacio. Field and laboratory studies have been carried out in order to elucidate the soil-forming processes taking place and to gain basic knowledge for a sustainable land management.Coarser soils are located near the present river system or in former riverbank areas, often under forest; textures here are loam or silty loam, silty clay loam being dominant. Finer soils may have up to 85% clay and are usually under savannah cover. Illite is the dominant clay mineral in all soils, followed by smectite and kaolinite; vermiculite is absent. Quartz is present in a very significant amount in the clay fraction of all studied soils. Goethite and lepidocrocite are present in all soils, lepidocrocite being a good indicator of poor drainage conditions.Soils are mainly acid, but there are soils with calcium carbonate accumulation in the subsoil, or even saline soils (salitrales). Soils are flooded for a significant period (3–6 months) and bypass flow is very active. Hydromorphic processes are always present and morphologies include hard and soft iron–manganese concretions with diffuse boundaries within peds, impregnative Fe coatings and Fe depletion hypocoatings along pore walls. The micromorphological study shows different degrees of hydromorphism, some of them associated to the present pore system and some with a palaeo character, often disturbed by active slickensides. Microsparite nodules are also present in some low-lying soils. The soils present several morphological features related to the mobility of the fine fraction that can be related to drainage conditions, as recent clay coatings, clay and silt infillings and coatings and clay-depleted hypocoatings. The most clayey soils show striated b-fabrics and frequent slickensides, and some others point to ferrolysis as iron-depleted hypocoatings and low crystallinity clay coatings along pores, although this is not supported by mineralogical data. A moderate cation supply probably prevents strong acidification.     

Micromorphological evidence of paleoenvironmental changes in Northern Cilento (South Italy) during the Late Quaternary

Three representative soil profiles developed during the Late Quaternary in Northern Cilento (South Italy) were studied by optical microscopy and SEM-EDS observation of thin sections to examine soil features as evidence for past climatic fluctuations.Two of the profiles are polygenetic and the third monogenetic. All these have a clear interglacial imprint, whereas the polygenetic profiles also contain other features, which can be related to periglacial conditions during the stadial glacial periods although in midlatitude coastal areas. All the paleosols show a strong marine influence during development, which probably resulted from windblown processes or submergence during past interglacial phases.     

The use of micromorphology in soil pollen analysis: The interpretation of the pollen content of slope deposits in Galicia, Spain

Humic horizons of soil profiles often contain pollen and spores. Comparison of the sequence of pollen associations of soil profiles with pollen zones of reference diagrams offers palyno-ecological information, relevant for reconstruction of landscape ecological development. In palynological studies of semiterrestrial and aquatic deposits, pollen is considered to be part of the sediment and anaerobic conditions in water-saturated deposits promote its conservation. This is not true for pollen in soils. Aerobic conditions in drained soils result in bio-oxidation of unprotected pollen grains. Interpretation of soil pollen associations requires knowledge of the processes of infiltration and conservation of pollen grains in the soil material. Micromorphology is an important technique to investigate these processes. This is demonstrated in a case study of polycyclic slope deposits in Galicia (Spain). The buried cambisols, in pleistocene solifluction deposits, contain post-sedimentary infiltrated pollen. The pollen associations reflect successive phases in soil ecological development. The holocene colluvial deposits contain syn-sedimentary incorporated pollen. The pollen associations reflect environmental conditions during the deposition of colluvial layers.     

Soil surface drip point features: an integrated approach using analytical photogrammetry and soil micromorphology

This study considers changes occurring on a soil surface after exposure to simulated rainfall. The soil surface in question has a crop cover of artificial maize, and interest focuses specifically on the surface features produced by leaf drips. An analytical photogrammetric approach is used to examine surface morphological change at a small scale (1 mm). These topographical changes are then related to sub-surface crust development as observed by the use of impregnated polished blocks. For the first time therefore soil surface and soil sub-surface changes are integrated together in one study. The results reveal a ‘cut and fill' type process in which aggregate welding and breakdown operate in parallel.     

Deep weathering and landscape evolution in a tropical plateau

The thick weathering profiles of humid tropical areas are an important, yet generally neglected, source of information on landscape evolution. Six complete profiles of the weathering mantle were sampled by drilling on the three stepped levels of the Campos do Jordão Plateau, on the NW flank of the Continental Rift of Southeastern Brazil. Mineralogical and micromorphological analyses of drill core samples, complemented by geochemical interpretations and by previous data on the upper saprolite, indicate continuity of a general lateritic trend during the entire process of mantle formation. Lateritization phases of different intensity were defined and considered to reflect adjustment to changes in environmental conditions created by the gradual uplift of the plateau to its present position. Older and more superficial materials related to intense lateritic weathering are characterized by allitization with direct formation of gibbsite from silicates, probably related to tropical climates existing immediately before the formation of the continental rift, during the Paleogene, and also before any significant increase in altitude. Monosialitization phase with general kaolinitization and restricted indirect formation of gibbsite from silicates could be associated to less aggressive climates that followed the Neogene (Miocene?) accentuation of uplift rates along the continental rift. The changes produced by uplift in the tropical climate eventually favored the development of a podzolization trend in soils above 1800 m.     

Genesis and characterization of manganiferous soils in the Eastern Piedmont, USA

Manganese is normally a trace element in soils, but it is important due to its effects on soil chemistry and morphology. There are rare, Mn-rich soils in the Eastern Piedmont of the USA that have not been previously studied. The morphology, mineralogy, and chemical and physical properties of these manganiferous soils were documented in order to better understand their pedogenesis. The soils were found to contain as much as 169 g kg⁻¹ Fe and 140 g kg⁻¹ Mn as oxides (dithionite-citrate-bicarbonate extractable). These high levels of Mn oxides impart an extremely dark color to the soil material (moist Munsell value and chroma commonly < 2/1). Manganiferous soil materials have unusual physical properties such as high particle density (up to 3.25 × 10⁻⁶ Mg m⁻³ on bulk soil), low bulk density (as low as 0.39 × 10⁻⁶ Mg m⁻³), and extremely high porosity (maximum calculated 88%). X-Ray Diffraction and Fourier Transform Infrared spectra show that the dominant Fe oxide and Mn oxide minerals in the soils are hematite and lithiophorite, respectively. Samples of the parent marble were dissolved in acid for Fe and Mn analysis and collection of non-carbonate residues (NCR). Based on the quantities of Fe and Mn in the bedrock, the mineralogy of the NCR, and micromorphological observations, it appears that the black, porous, Mn-rich material is derived directly from the dissolution of marble bedrock and accumulation of silicate residues plus Mn and Fe from within the rock. These soils, which appear to have a similar origin to Mn wad deposits, offer a unique opportunity for future studies of soil Mn due to the naturally high concentration of this metal.     

Root–soil adhesion as affected by crop species in a volcanic sandy soil of Mexico

Field observations have shown that root residues maintain root-adhering soil for several months after harvest. The aim of this work was to compare post-harvest effect of Amaranthus hypochondriacus (amaranth), Phaseolus vulgaris (common bean) and Zea mays (maize) roots on root-adhering soil, aggregation and organic carbon content. The experimental site was located on a volcanic sandy soil (Typic Ustifluvent) in the Valley of Mexico. In 1999 and 2000, maize had the highest root mass (92 and 94 g m⁻²) and the highest root-adhering soil (9051 and 5876 g m⁻²) when a root–soil monolith of 0.20 m × 0.20 m × 0.30 m was excavated after harvest. In contrast, bean roots (2 and 5 g m⁻²) had only 347 and 23 g m⁻² of adhering soil per monolith in each year. Amaranth had intermediate values between maize and bean. Dry soil aggregate classes (<0.25, 0.5, 1, 2, 5 and >5 mm) were similarly distributed among the three species. The sum of the three soil macro-aggregates classes >1 mm was 0.1 g g⁻¹ in both years. Neither water stability of the 2–5 mm aggregates (0.05–0.09 g g⁻¹) nor soil organic C (SOC) in three aggregate classes (<0.25, 1–2 and >5 mm; mean 14.6 mg g⁻¹) was affected by species (P < 0.05) in either year. Observations of thin sections (10× and 40×) revealed absence of macro-aggregates under maize. Soil compaction was attributed to high mass of maize roots in the sampled soil volume. Root systems sampled after harvest had the capacity to maintain a well structured soil mass, which was proportional to root mass. Root-adhering soil measured in the field could be used to select species promoting soil adhesion by roots.     

Morphological characterisation of humus forms in recent coastal dune ecosystems in Belgium and northern France

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.     

Variability at the electron microscopic level in leaves of members of the genus Vitis

Scanning electron microscopy (SEM) was used to examine the characteristics of the upper and lower sides of leaves belonging to members of the genus Vitis – 11 vinifera varieties (‘Albariño’, ‘Treixadura’, ‘Caíño Blanco’, ‘Mencía’, ‘Chasselas’, ‘Cabernet Sauvignon’, ‘Alicante Bouschet’, ‘Godello’, ‘Torrontés’, ‘Blanco Legítimo’ and ‘Caíño Tinto’) and three non-vinifera varieties (‘110-Ritcher’, ‘SO4’ and ‘Jacquez’). All the genotypes studied grew in the same plot, were of the same age, and had been raised following the same cultivation practices. The leaves examined were taken from node 8 of a fruiting shoot growing from the previous year's wood. The same part of the leaf – the area between the main vein and the first right lateral vein – was examined in all plants. SEM observations were made at 200×, 655× and 2000×. Photomicrographs and drawings were prepared reflecting the observed morphology of the upper and lower leaf surfaces. Variables such as cell density, cell surface area (in the horizontal plane) and stomatal density and surface area (in the horizontal plane) were measured for both leaf surfaces, and intra- and inter-varietal differences recorded. The upper leaf surfaces of all the studied genotypes were similar, but clear differences were recorded for the lower sides.     

委陵菜属植物叶表皮微形态及其与环境关系

[目的]研究叶表皮特征在委陵菜属植物分类中的应用价值,同时对其与环境的关系进行讨论。[方法]利用光学显微镜对大庆地区9种委陵菜属植物叶表皮的形态特征及其与环境关系进行了观察和研究。[结果]9种委陵菜表皮细胞为多边形、近多边形和不规则形状;垂周壁式样出现近平直、弧形、浅波形和波形的分化;气孔器均为无规则型,随机分布;表皮毛有3种类型：单细胞直的不分枝毛、单细胞卷曲不分枝毛和腺毛。[结论]该研究为委陵菜属植物的系统分类及合理开发利用提供了更丰富的资料和依据。