Stanislav Pen-Mouratov

Responses of nematode community structure to pesticide treatments in an arid ecosystem of the Negev Desert

The aim of this study was to determine the effect of pesticides on free-living soil nematodes in a desert system. Spatial and temporal distributions as well as changes in nematode community structure were investigated. Soil samples were collected monthly between November 2000 and November 2001 from four plots: one treated with Nemacur, one with Edigan, one with water and one untreated plot as control. The nematode population as well as spatial distribution was found to be affected by treatments on a temporal basis. The different treatments applied led to a significant difference in the abundance of nematode trophic groups, where the fungivores and bacterivores were found to decrease in the pesticide-treated samples. A total of 31 genera were found in the samples, with 21 in the Nemacur-treated sample and 16 in the Edigan-treated sample. Ecological indices such as trophic diversity, maturity index and Shannon index elucidated the effect of pesticides on density, diversity and trophic group composition.

Coupling geochemical, mineralogical and microbiological approaches to assess the health of contaminated soil around the Almalyk mining and smelter complex, Uzbekistan

This study describes the impact of airborne pollution resulting from mining and smelting activities on the soils of the Almalyk mining and industrial area (NE Uzbekistan). Samples were collected along a transect downwind of the industrial area. Enriched contents of some metals were found in the upper soil layers near the metallurgical complex (Zn≤3010 mg kg(-1), Pb≤630 mg kg(-1), Cd≤30 mg kg(-1)) which suggests that these metals were derived from local stack emissions. The morphology and internal microstructure of metal-bearing spherical particles found in the heavy mineral fraction suggest that these particles were probably a result of inefficient flue gas cleaning technique of the smelter. The highest metal concentrations were found also in soil solutions and exchangeable solid fractions from the first three locations, and decreased with increasing distance from the pollution source along transect. Thermodynamic equilibrium calculations suggest that the mobile metal pool in the contaminated soil is mainly controlled by dissolution of metal carbonates formed as weathering product of the metalliferous particles. The health of the microbiological soil ecosystem was assessed by measurements of basal respiration, nematode abundance, biomass-related C and N content, and microbial metabolic quotient qCO2. Significant correlations were found between the dissolved metal content and the microbiological health parameters, a negative one for Cmic/Corg ratio, and a positive one for qCO2. A negative correlation was found between the amount of nematodes and the metal contents suggesting that the contaminated soil has significant impact on the functioning of the microbiological community. A better understanding of the spatial variations in the whole ecosystem functioning due to airborne impact could be very useful for establishing suitable land use and best management practices for the polluted areas.

Research Note: Spatial Variation of AM Fungal Spore Numbers under Canopies of Acacia raddiana

The spatial variation of arbuscular mycorrhizal fungal spores under the canopy of Acacia raddiana was studied in a desert system. Soils samples from the base of the stem, its canopy radius, and outside its canopy at four stations in the Negev desert were collected from a 0 to 50 cm depth at sections of 10 cm each. The mean spore density was found to fluctuate between 265 100 g−1 to 105 100 g−1 in fluvisols and calcaric fluvisols, respectively. Our results suggest that spore density and spore distribution were found to be directly correlated with soil type, elucidating the importance of soil physical composition on AM fungi distribution in desert soil ecosystems.

Soil Biota in the Arava Valley of Negev Desert, Israel

Abstract Soil microorganism biomass and respiration and the soil nematode community were observed in the hypersaline desert valley that is found between the Dead Sea and the Red Sea. The lowest point of the valley is approximately 400 m below sea level, and is the lowest point on earth. Soil samples ( n = 72) were collected from the 0–10 and 10–20 cm soil layers at different altitudes (from −400 to +100 m) in the open spaces between plants during one of the most extreme xeric periods. Both soil microbial respiration and microbial biomass were found to be negatively dependent on soil moisture (SM) and organic matter (OM), and positively dependent on pH values. The physical-chemical characteristics of this hypersaline area were extremely unfavorable for the soil nematode communities, and the nematodes were entirely absent in the open area below sea level. The bacterivores were found to be the most resistant nematodes in this hyperarid region, with the Wilsonema being the most widespread genus. We suggest that nitrogen availability may play a crucial role in the below-ground soil interaction in this region, with bacterivore nematodes as indicators of nitrogen availability.

Spatio-Temporal Effect on Soil Respiration in Fine-Scale Patches in a Desert Ecosystem

ABSTRACT Soil organisms in terrestrial systems are unevenly distributed in time and space, and often aggregated. Spatio-temporal patchiness in the soil environment is thought to be crucial for the maintenance of soil biodiversity, providing diverse microhabitats tightly interweaving with resource partitioning. Determination of a “scale unit” to help understand ecological processes has become one of the important and most debatable problems in recent years. A fieldwork was carried out in the northern Negev Desert highland, Israel to determine the influence of fine-scale landscape patch moisture heterogeneity on biogeochemical variables and microbial activity linkage in a desert ecosystem. The results showed that the spatio-temporal patchiness of soil moisture to which we attribute influential properties, was found to become more heterogenic with the decrease in soil moisture availability (from 8.2 to 0.4 g kg−1) toward the hot, dry seasons, with coefficient of variation (CV) change amounting to 66.9%. Spatio-temporal distribution of organic matter (OM) and total soluble nitrogen (TSN) was found to be relatively uniformly distributed throughout the wet seasons (winter and spring), with increase of relatively high heterogeneity toward the dry seasons (from 0.25% to 2.17% for OM, and from 0 to 10.2 mg kg−1 for TSN) with CV of 47.4% and 99.7% for OM and TSN, respectively. Different spatio-temporal landscape patterns were obtained for Ca (CV = 44.6%), K (CV = 34.4%), and Na (CV = 92%) ions throughout the study period. CO2 evolution (CV = 48.6%) was found to be of lower heterogeneity (varying between 2 and 39 g CO2-C g−1 dry soil h−1) in the moist seasons, e.g., winter and spring, with lower values of respiration coupled with high heterogeneity of Na+ and low levels of TSN and organic matter content, and with more homogeneity in the dry seasons (varying between 1 and 50 g CO2-C g−1 dry soil h−1). Our results elucidate the heterogeneity and complexity of desert system habitats affecting soil biota activity.

Successive development of soil ecosystems at abandoned coal-ash landfills

The main goal of the present study was to determine the effect of the native vegetation on the successive development of the soil ecosystem at abandoned coal-ash landfills of the Angren coal-fired power plant in Uzbekistan. Two different landfills (one not in use for 3 years, termed newer, and the other not in use for 10 years, termed older) with different degrees of vegetation cover were chosen to assess the time and vegetation effects on soil biota and habitat development. The soil biotic structure, including soil microorganisms and soil free-living nematode communities, was investigated both at open plots and under different native plants at the coal-ash landfill area. The observed soil microorganisms were found to be the most important component of the observed ecosystems. Total abundance, biomass, species, trophic and sexual diversity of soil free-living nematodes, along with fungi and organic-matter content, were found to be correlated with trace metals. The nematode trophic and species abundance and diversity increased from the newer toward the older coal-ash landfills. The sex ratio of the nematode communities was found to be dependent on the environmental conditions of the study area, with the males being the most sensitive nematode group. All applied ecological indices confirmed that open landfill plots distant from plants are the most unfavorable areas for soil biota. In that respect, the native plants Alhagi maurorum Desv. and Tamarix sp. were found to be important environmental components for the natural remediation of a soil ecosystem in the coal-ash landfill area.

Do slope orientation and sampling location determine soil biota composition

Abstract“Evolution Canyon” is a typical Mediterranean-basin canyon with a summer dry stream at the bottom and large differences in vegetation cover and solar radiation between the north-facing slope (NFS) and the south-facing slope (SFS). It is known to act as an abiotic mediator influencing the community structure of soil fauna. The aim of this study was to determine the spatial dispersion of soil microbial and free-living nematode communities in the open sites (between shrubs) in the upper (0–10 cm) soil layer at four altitudes on both slopes. The combination of relative soil moisture availability and temperature, known to be one of the main triggers for soil biota activity, was explained by slope orientation. The above-mentioned differences were found to significantly affect microbial biomass and CO2 evolution resulting in temporary stress, corresponding to higher values in metabolic quotient (qCO2) values. These differences may represent microbial investment in energy in order to overcome stress resulting from the microclimatic differences between the two slopes. Moreover, the degree of substrate limitation (primary production due to the differences in plant cover) of microbial activity was explained by the difference in microbial functional groups. The total abundance of soil free-living nematodes was found to be 2-fold higher on the SFS than on the NFS. Thirty-nine genera, including 12 bacteria-feeders, 5 fungi-feeders, 12 plant-parasites, and 10 omnivore-predators, were found at the study site, with 34 genera on the NFS and 29 on the SFS. The generic diversity of the bacteriafeeding nematodes was higher on the SFS than on the NFS. This study elucidates the importance of slope orientation and its effect on the structural levels of soil microbial and nematode communities.

Distribution of Soil Microbial Biomass and Free-living Nematode Population in Terrace Chronosequences of Makhtesh-Ramon Crater

ABSTRACT In this study, we examined the effects of the age of erosional fluvial terraces of Makhtesh Ramon (Ramon crater) in the central Negev Desert on soil chemical and biological properties. There were significant effects of erosion age of these terraces on soil moisture, organic carbon, soil salinity, and electrical conductivity. It is known that soil biological activity in arid ecosystems is determined by well-known limiting factors such as soil moisture and organic matter. Significant (P < 0.002) differences in total nematode population and microbial biomass [(22.0–3.4 Cmic (µg C g−1 soil)] were observed between terraces. Biological activity of soils in lower and younger terraces was greater than in older and higher terraces. The ecophysiological status (qCO2) of the soil microbial community was found to decrease from a maximal value of 1.3 to 0.32 mg CO2‒C (gCmich)−1 along the terraces (from younger to older ones). This study illustrates the integrated effect of age, altitude, and the morphostratigraphic position of terraces on the biological activity of soils.

Effect of sand-dune slope orientation on soil free-living nematode abundance and diversity

SummaryThe spatial and temporal dynamics and composition of a soil free-living nematode community were studied in order to determine the impact of slope orientation on the community on the xeric south- and the mesic north-facing sand-dune slopes.A significant effect of sampling location on organic matter, total number of free-living nematodes, and trophic diversity was found. Although soil moisture had a significant effect on separate nematode trophic groups and on most of the applied ecological indices, no differences in soil moisture were observed between slopes. Organic matter was found to have a significant effect on the fungivore nematodes. The obtained results indicate that the south-facing slope is more favorable for the observed free-living nematodes than the other sampling sites. Twenty-four of the 77 nematode species that were found in the observed area showed dependence on dune slope orientation. The fungibacteria ratio, Simpson’s dominance index, and basal index were useful tools for determining slope differences.

Seasonal Effect of Geomorphological Chronosequence Features on Soil Biota Dynamics

Numerous studies have been devoted to the physical-chemical weathering processes leading to the creation of unique soil formations having their own history that induce soil-biotic diversity. However, the extent to which unique geomorphic formations influence soil biotic seasonal variation is not clear. Our aim was to define seasonal variations of soil biota in soils of different-aged terraces of the Makhtesh Ramon anticline erosional cirque in southern Israel. The strong effect of Makhtesh Ramon (Ramon crater) erosional fluvial terrace age initiated by climatic changes during the Late Pleistocene- Early Holocene period on seasonal variations in both soil properties and the abundance and composition of soil biota were demonstrated. However, age dependence was not constant and values for observed soil properties and microbial activity were negligible between younger and older terraces for certain seasons, while free-living nematodes along with bacterial-feeding group were strongly dependent on the geomorphic features of the ages throughout the study period.