Humus profiles of Siberian soils under different forming conditions

Humus profiles of Siberia soils under different conditions and models of soil formation are considered in the paper. It is shown that the humus profiles of soils formed in the regions of displacement of landscape and soil borders and developed according to the polygenetic model as well as the soils of synlithogenous type of pedogenesis have a complicated structure. Simple structure of the humus profile characterizes soils developing within the framework of a simple (ideal, normal) model of soil formation.     

Denitrification studies in a temperate forest catena soil

Summary Formation of ammonium during the reduction of nitrate under moderate and strict anaerobic incubation of two topsoils of a temperate forest catena, an acid mull and an anmoor was studied. In mull, both conditions of incubation caused reduction of nitrate and release of ammonium. The accumulation of ammonium continued even when there was no nitrate left hence indicating the formation of ammonium apparently through desamination of organic matter. Whereas, in anmoor neither any such formation of ammonium nor any significant reduction of nitrate was observed in the case of moderate anaerobic incubation. But under strict anaerobic incubation, progressive disappearance of nitrate was encountered from the beginning up to 30 days and this was accompanied by an increasing accumulation of ammonium in this soil. Yet this accumulation stopped when there was no nitrate left. Thus, the formation of ammonium is caused by the reduction of nitrate in anmoor.     

Vertical profiles of microbial communities in perfluoroalkyl substance-contaminated soils

Poly- and perfluoroalkyl compounds (PFASs) are ubiquitous in the environment, but their influences on microbial community remain poorly known. The present study investigated the depth-related changes of archaeal and bacterial communities in PFAS-contaminated soils. The abundance and structure of microbial community were characterized using quantitative PCR and high-throughput sequencing, respectively. Microbial abundance changed considerably with soil depth. The richness and diversity of both bacterial and archaeal communities increased with soil depth. At each depth, bacterial community was more abundant and had higher richness and diversity than archaeal community. The structure of either bacterial or archaeal community displayed distinct vertical variations. Moreover, a higher content of perfluorooctane sulfonate (PFOS) could have a negative impact on bacterial richness and diversity. The rise of soil organic carbon content could increase bacterial abundance but lower the richness and diversity of both bacterial and archaeal communities. In addition, Proteobacteria, Actinobacteria, Chloroflexi, Cyanobacteria, and Acidobacteria were the major bacterial groups, while Thaumarchaeota, Euryarchaeota, and unclassified Archaea dominated in soil archaeal communities. PFASs could influence soil microbial community.     

Long term 15N studies in a catena of the shortgrass steppe

A set of long term¹⁵N studies was initiated during the summers of 1981 and 1982 on the backslope and footslope, respectively, of a catena in the shortgrass steppe of northeastern Colorado. Microplots labeled with¹⁵N urea were sampled for¹⁵N and total N content in 1981 and 1982 and again in 1992. In November, 1982, 100% of the added N was recovered in the soil-plant system of the finer-textured footslope, compared to 39% in the coarser-textured backslope microplots. Ten years later,¹⁵N recovery of the applied N decreased at both topographic positions to 85% in the footslope and 29% in the backslope. Average losses since the time of application were 3.5 g N m^–2yr^–1 in the backslope and 0.8 g N m^–2yr^–1 in the footslope. In 1992, soil organic matter was physically fractionated into particulate (POM) and mineral associated (MAON) fractions and 21-day mineralization incubations were conducted to assess the relative amounts of¹⁵N that were in the slow, passive and active soil organic matter pools, respectively, of the two soils. Our findings confirm the assumptions that POM represents a large portion of the slow organic compartment and that the MAON represents a large fraction of the passive compartment defined in the Century model. The N located in the MAON had the lowest availability for plant uptake. Isotopic data were consistent with textural effects and with the Century model compartmentalization of soil organic N based on the residence time of the organic N.     

Humus status of different soils affected by pollution with fluorides from aluminum production in the Baikal region

The effect of pollution by fluorides from aluminum production on the humus status in different types of arable soils was studied in field experiments. They included modeling of a high pollution level by addition of NaF prevailing in industrial air emissions. The negative effect of fluorides on the humus status, related to an increase in the mobility of humic substances, was more pronounced in gray forest soil than in sod-meadow soil. This depended on the soil physicochemical properties determining the buffer capacity toward NaF and the content of water-soluble fluorides.     

Vegetation structure and biodiversity along the eucalypt forest to rainforest continuum on the serpentinite soil catena in a subhumid area of Central Queensland,Australia

Abstract The deep lateritic earths that cap the serpentinite outcrop in the Rockhampton – Marlborough area on the Tropic of Capricorn in Central Queensland have been eroded to expose the underlying ultramafic rock. Water‐holding capacity of these nutrient‐poor soils increases in a gradient from the skeletal soils to the deep lateritic earths and results in a continuum of structural formations from open‐woodland to woodland to open‐forest. A couple of closed‐forest (rainforest) stands have developed where seepage into Marlborough Creek occurs throughout the year. Aerodynamic fluxes (frictional, thermal and evaporative) in the atmosphere as it flows over and through the vegetation influence the annual foliage growth in all strata in the continuum from skeletal soils to deep lateritic earths. The lateral growth of each plant is abraded so that the sum of the foliage projective covers of overstorey (FPCo) and understorey (FPCu) strata – that is Σ(FPCo + FPCu) – remains constant throughout the serpentinite soil catena. As more water becomes available in the soil catena, the mineral nutrient levels in overstorey leaves increase, making developing leaves more vulnerable to insect attack. Although the number of leaves produced annually on each vertical foliage shoot in the overstorey increases along the soil‐water gradient, Σ(FPCo + FPCu) remains constant in all stands. The carbon isotope ratios (a measure of stomatal resistance) and leaf specific weights (LSWs) (a measure of the proportion of structural to cytoplasmic content in a leaf) of overstorey and understorey strata, however, are constant throughout the continuum. The well‐watered rainforest pockets – where seepage occurs – form the end point of this serpentinite continuum. LSWs and carbon isotope ratios of the canopy trees are similar to those in the sheltered understorey in the eucalypt communities. A gradient of foliage attributes is observed from evergreen canopy trees (12 m) to subshrubs (2 m) in the sunlit life forms that compose the complex structure of the rainforest stands in the humid to subhumid climate of Central Queensland. As alpha diversity (number of species per hectare) is correlated with annual shoot growth per hectare, species richness along the serpentinite continuum is almost half that of nearby plant communities on medium‐nutrient soils. The one to two eucalypt species per hectare are about a tenth of the number recorded on adjacent medium‐nutrient soils.     

15N abundance of surface soils,roots and mycorrhizas in profiles of European forest soils

¹⁵N natural abundances of soil total N, roots and mycorrhizas were studied in surface soil profiles in coniferous and broadleaved forests along a transect from central to northern Europe. Under conditions of N limitation in Sweden, there was an increase in ¹⁵N of soil total N of up to 9% from the uppermost horizon of the organic mor layer down to the upper 0–5 cm of the mineral soil. The ¹⁵N of roots was only slightly lower than that of soil total N in the upper organic horizon, but further down roots were up to 5% depleted under such conditions. In experimentally N-enriched forest in Sweden, i.e. in plots which have received an average of c. 100 kg N ha^–1 year^–1 for 20 years and which retain less than 50% of this added N in the stand and the soil down to 20 cm depth, and in some forests in central Europe, the increase in ¹⁵N with depth in soil total N was smaller. An increase in ¹⁵N of the surface soil was even observed on experimentally N-enriched plots, although other data suggest that the N fertilizer added was depleted in¹⁵N. In such cases roots could be enriched in¹⁵N relative to soil total N, suggesting that labelling of the surface soil is via the pathway: — available pools of N-plant N-litter N. Under N-limiting conditions roots of different species sampled from the same soil horizon showed similar ¹⁵N. By contrast, in experimentally N-enriched forest ¹⁵N of roots increased in the sequence: ericaceous dwarf shrubs15N enriched compounds in fungal material, which could contribute to explain the observed ¹⁵N profiles if fungal material is enriched, because it is a precursor of stable organic matter and recalcitrant N. This could act in addition to the previous explanation of the isotopically lighter soil surface in forests: plant uptake of ¹⁵N-depleted N and its redeposition onto the soil surface by litter-fall.     

Cyanobacterial nitrogen fixation in arid soils of Central Australia

Abstract The distribution of nitrogen-fixing cyanobacteria was studied in two regions of Central Australia, one near Yulara and the other in the Ti-Tree Basin. Soil and other samples were tested in situ for nitrogen fixation by the acethylene reduction assay. They were then enriched in low light in suitable growth medium containing no fixed carbon or nitrogen over a period of months. The cyanobacterial components were identified and their nitrogen-fixing capacity measured again both in the light and in darkness. It is concluded that a variety of genera of cyanobacteria survive in the arid region of Central Australia and can be assumed to contribute fixed nitrogen to the soils of the region.     

Plant indicators of alluvial soils of Central Iraq

Summary The alluvial soils of Central Iraq are occupied by 4 main vegetation types. The soils under the riverian vegetation are characterised by medium salinity and high proportions of bivalent cations. The soils occupied by arid scrub vegetation have comparatively higher contents of clay and small amounts of soluble salts. The soils of the halophytic vegetation are highly saline and main component of this is sodium chloride. The soils under the aquatic vegetation are highest in organic matter and low in salinity.     

Microbial diversity of topographical gradient profiles in Fushan forest soils of Taiwan

To evaluate the microbial diversity of Fushan forest soils, the variation of soil properties, microbial populations, and soil DNA with soil depth in three sites of different altitude were analyzed. Microbial population, moisture content, total organic carbon (C_org), and total nitrogen (N_tot) decreased with increasing soil depth. The valley site had the lowest microbial populations among the three tested sites due to the low organic matter content. Bacterial population was the highest among the microbial populations. The ratios of cellulolytic microbes to the total bacteria in organic layers were high, implying their roles in the carbon cycle. The microbial biomass carbon (C_mic) and nitrogen (N_mic) contents ranged from 130.5 to 564.1 μg g⁻¹ and from 16.7 to 95.4 μg g⁻¹, respectively. The valley had the lowest C_mic and N_mic. The organic layer had the highest C_mic and N_mic and decreased with soil depth. Analysis using denaturing gradient gel electrophoresis (DGGE) of polymerase chain reaction (PCR) amplicons of 16S rDNA showed that the bacterial diversity of the three sites were very similar to each other in the major bands, and the variation was in the minor bands. However, the patterns in PCR-DGGE profile through gradient horizons were different, indicating the prevalence of specific microbes at different horizons. These results suggest that the microbial diversity in the deeper horizons is not simply the diluted analogs of the surface soils and that some microbes dominate only in the deeper horizons. Topography influenced the quantity and diversity of microbial populations.     

Soil nutrients distribution and moisture dynamics on upper catena in a semi-arid nature reserve

The distribution of soil nutrients and soil moisture dynamics on slopes of catenary landscape, were recorded in a semi-arid nature reserve located in the Eastern Transvaal, South Africa. Soil nutrients were accumulating in the slopes of the catena whereas the crests were highly leached. Open grassland bands segregating between the two soil types and their associated plant species, did not show clear stratification of nutrient deposition amongst ground levels down to 1.5 m below the surface. There was however, a tendency of soils with high nutrient contents to correlate with areas of high woody vegetation density. Patterns of soil moisture levels during two annual rainfall periods showed some segregation between soil depths, although the trends indicated that the duration of saturation and dry out of soils levels differed more between rainy seasons than between soil levels during a particular season.     

Cooperation in two-person evolutionary games with complex personality profiles

We propose a theory of evolution of social systems which generalizes the standard proportional fitness rule of the evolutionary game theory. The formalism is applied to describe the dynamics of two-person one-shot population games. In particular it predicts the non-zero level of cooperation in the long run for the Prisoner's Dilemma games, the increase of the fraction of cooperators for general classes of the Snow-Drift game, and stable nonzero cooperation level for coordination games.     

The Asplenium trichomanes complex in East Central Sweden

An investigation of the Asplenium trichomanes complex in some Swedish provinces is presented. The study comprises ssp. trichomanes 2n = 72, ssp. inexpectans 2n = 72, ssp. quadrivalens 2n = 144 and a triploid hybrid 2n = 108. The ssp. inexpectans is reported from Sweden for the first time. It is previously only known from Central and Southern Europe. It was found to be about as common as the other two subspecies occurring in Sweden.     

Radiography of peat profiles: a fast method for detecting human impact on vegetation and soils

The value of radiographic investigation of peat cores for detecting deposited mineral particles on peat surfaces in the past is demonstrated. In small peat bogs this mineral deposition often reflects sand erosion associated with human activity in the vicinity of the bog. The technique provides important additional stratigraphic and environmental information. The methods are described and illustrated with reference to investigations of human impact on past vegetation in the area of Kosel, Schleswig-Holstein, Northern Germany. Results of radiography and measurements of ash content are compared with the anthropogenic indicators in the pollen record.     

Microbial communities of frozen soils of the Tuimaada Valley in Central Sakha

This study determined the characteristic features of microbial communities inhabiting frozen soils of Central Sakha. All groups of microorganisms were present in high numbers comparable with the microbial densities in steppe soils of Transbaikalia; their distribution along soil profiles followed a specific pattern with no decrease in abundance with depth. In summer, the dominant groups of the microbial pool were actinomycetes and oligonitrophilic bacteria, while in autumn it was heterotrophic bacteria. A typical feature of the frozen soils of Central Sakha was the gradual penetration of microorganisms into deeper soil horizons during the vegetation season and their accumulation in the suprapermafrost horizon by autumn.     

Plasmid profiles of Mycobacterium avium complex isolated from swine

Twenty strains of Mycobacterium avium complex (MAC) isolated from swine and five strains from humans were examined for drug susceptibility and plasmid content. Four strains of swine origin and two strains of human origin harbored plasmid DNAs differing in molecular weights. No relationship between plasmid contents and drug resistance was observed. Southern DNA-DNA hybridization showed that small plasmids from swine MAC strains were homologous to those from human origin at the nucleotide level.     

Determinacy and synchronicity of fallow succession in the Tuva steppes

Succession on five fallows of Tuva has been studied. It has been shown that the fallow succession proceeds regularly and synchronously. Under the arid conditions of Tuva, weeds are developed at the initial stage of the succession (0–4 years). The first intermediate stage (4–7 years) on all fallows is characterized by the absolute predominance of weeds and the appearance of dominants typical for specific steppes. At the second intermediate stage (7–11 years), the species of aboriginal steppes dominate on all fallows. At the late stage (11–17 years), terminal communities with the combinations of species typical for each steppe, including predominant species, are developed.     

Phospholipid fatty acid composition of microorganisms in pine forest soils of Central Siberia

The phospholipid fatty acid (PLFA) composition of microorganisms in podzolic soils of pine forests was studied in Central Siberia. The live microbial biomass in the 1-m mineral soil layer was found to gradually decrease with depth. Although the biomass decreased by half in the lower horizons, its content remained sufficiently high (12–14 nmol FAs/g soil). The coefficient of similarity in the fatty acid composition between the soils of forest and open (unforested) sites was 0.85. The coefficient of fatty acid richness in the mineral soil layer decreased with depth, while differences in fatty acid profiles increased.     

Evaluating environmental conditions of a temporary pond complex using rotifer emergence from dry soils

In this study we evaluated the usefulness of rotifer emergence from dry soils to indicate the environmental status of a remnant temporary pond complex in an agricultural area in central Spain. Because the ponds did not flood during our project, emergence was studied in relation to environmental variables in outdoor microcosms. Redundancy analysis and nestedness analysis showed that salinity and total nitrogen concentrations shaped the emerged communities. Depauperate rotifer assemblages from pond microcosms with higher salinity and nitrogen levels were nested subsets of species-rich communities from microcosms of less enriched sites. Rotifer community structure also identified small ponds as reference sites that should receive priority in conservation and degradation mitigation programs. Results suggest that rotifer emergence from rewetted sediments using microcosms can be useful for evaluating the nutrient status during the dry phase of temporary wetlands. While results from this approach are conservative, requiring comparisons with field observations, their tentative value lies in alerting management and providing a basis for future research of poorly studied but threatened temporary habitats. Rotifer emergence could be a useful alternative to traditional biological indicators of nutrient status that depend on the presence of water.