Ascospore morphology of bryophilous Pezizales is closely associated with the place of infection and host ecology

Fungal spores are morphologically highly diverse and are therefore frequently used as diagnostic characters in taxonomy. However, the connection between spore morphology and fungal ecology remains poorly understood. Using phylogenetic comparative analyses, we investigated the putative relationships between four ascospore traits and the dominant place of infection, host ecology, and host taxonomic placement in 123 species of biotrophic parasites of bryophytes. Ascospore shape, ornamentation height and relative lipid content are significantly correlated in bryophilous Pezizales. Species attached by their hyphae to bryophyte rhizoids have more globose ascospores with higher ornamentation and relative lipid content than species attached to aboveground organs. Furthermore, some ascospore traits are significantly associated with host lifespan, habitat preferences, and taxonomic placement of their host bryophytes. Our results suggest that the ascospore morphology in this fungal group is closely linked to its ecology and several of the detected relationships point to the existence of distinct dispersal strategies.     

The Inter-Valley Soil Comparative Survey: the ecology of Dry Valley edaphic microbial communities

Recent applications of molecular genetics to edaphic microbial communities of the McMurdo Dry Valleys and elsewhere have rejected a long-held belief that Antarctic soils contain extremely limited microbial diversity. The Inter-Valley Soil Comparative Survey aims to elucidate the factors shaping these unique microbial communities and their biogeography by integrating molecular genetic approaches with biogeochemical analyses. Although the microbial communities of Dry Valley soils may be complex, there is little doubt that the ecosystem''s food web is relatively simple, and evidence suggests that physicochemical conditions may have the dominant role in shaping microbial communities. To examine this hypothesis, bacterial communities from representative soil samples collected in four geographically disparate Dry Valleys were analyzed using molecular genetic tools, including pyrosequencing of 16S rRNA gene PCR amplicons. Results show that the four communities are structurally and phylogenetically distinct, and possess significantly different levels of diversity. Strikingly, only 2 of 214 phylotypes were found in all four valleys, challenging a widespread assumption that the microbiota of the Dry Valleys is composed of a few cosmopolitan species. Analysis of soil geochemical properties indicated that salt content, alongside altitude and Cu²⁺, was significantly correlated with differences in microbial communities. Our results indicate that the microbial ecology of Dry Valley soils is highly localized and that physicochemical factors potentially have major roles in shaping the microbiology of ice-free areas of Antarctica. These findings hint at links between Dry Valley glacial geomorphology and microbial ecology, and raise previously unrecognized issues related to environmental management of this unique ecosystem.     

Molecular and biochemical aspects of rhizobacterial ecology with emphasis on biological control

The rhizosphere is the narrow zone of soil surrounding the root that is subject to influence by the root. Rhizobacteria are plant-associated bacteria that are able to colonize and persist on roots. An understanding of the ecology of a microorganism is a fundamental requirement for the introduction of a microbial inoculant into the open environment. This is particularly true for biological control of root pathogens in the rhizosphere, where one is actively seeking to alter the ecological balance so as to favour growth of the host plant and to curtail the development of pathogens. Some strains of plant growth-promoting rhizobacteria can effectively colonize plant roots and protect plants from diseases caused by a variety of root pathogens and growth promotion of plants through direct stimulation of growth hormone. Such beneficial or plant health-promoting strains are emerging as promising biocontrol agents. They are suitable as soil inoculants either individually or in combination and may be compatible with current chemical pesticides. Considerable progress has been achieved using molecular genetic techniques to elucidate the important microbial factors or genetic traits involved in the suppression of fungal root diseases. Strategies utilizing molecular genetic techniques have been developed to complement the ongoing research ranging from the characterization and genetic improvement of a selected biocontrol agent to the measurement of its persistence and dispersal. Finally, biocontrol is considered as part of a disease control strategy like integrated pest management which offers a successful approach for the deployment of both agro-chemicals and biocontrol agents.     

Influence of ecological and edaphic factors on biodiversity of soil nematodes

Nematodes are the most diverse and highly significant group of soil-inhabiting microorganisms that play a vital role in organic material decomposition and nutrient recycling.Diverse geographical locations and environmental gradients show a significant impact on the diversity of nematodes. Present study aims to assess the effects of ecological (altitude, temperature, moisture) and edaphic (soil pH, nutrients, soil patches) factors on the soil nematode diversity and structure at five different landscape patches (forests, apple orchards, rice fields, pastures, and alpine zone) from ten different sites of Kashmir valley (India). Differences in the altitudinal gradients results in the shift of generic nematode population. Among the soil patches, highest nematode diversity was observed in forest soil and least in alpine soil; however, bacteriovorous nematodes dominated all the soil patches. The temperature and moisture have a significant effect on nematode diversity, the highest nematode trophic levels were observed above 21°C temperature, and 30% moisture. Nematode abundance decreased from alkaline to acidic pH of the soil. Soil nutrients such as, nitrogen (N) and phosphorus (P) have shown a detrimental effect in nematode richness at each site, where nematode diversity and richness of genera were higher at abundant soil N and P but decreased at low soil nutrients. Ecological indices like diversity index (DI), Shannon-Wiener Index (H'), enrichment index (EI), and maturity Index (MI) values demonstrated forest soil more favourable for nematodes and high soil health status than other soil patches. This study suggested that these indices may be helpful as soil monitoring tools and assessing ecosystem sustainability and biodiversity.     

The effect of competition and edaphic conditions on the establishment of halophytes on brine effected soils

In order to test the feasibility of using native halophytes to reclaim brinecontaminated soil, seedlings of five inland halophytes, Atriplexprostrata, Hordeum jubatum, Salicornia europaea, Spergularia marina, and Suaeda calceoliformis, were planted at threedensities on a site near Athens, Ohio which had been contaminated by oilwell brine water. Ten replicates of each density treatment weretransplanted on two distinct areas of high and low salinity in May of 1993. Seedling survivorship, soil moisture, and soil salinity were monitored weeklythroughout the growing season. Biomass production and ion uptake weredetermined for each plant surviving until harvest. Soil analyses wereperformed prior to planting and after harvest to determine overall changesin soil chemistry and to determine the amount of Na⁺ reductionfrom the soil due to leaching by precipitation during the course of theexperiment. Survival was determined to be density independent for all ofthe species with the exception of S. marina where survival wasfacilitated at high density. Increased salinity negatively affected the survivaland yield of A. prostrata. The remaining species had greater survivalunder high salinity conditions, and density appeared to be the key factorinfluencing yield. Sodium and chloride ions were accumulated in planttissues in much greater amounts than K⁺, Ca⁺²or Mg⁺². Salicornia europaea plants grown in high densityon the high salinity site accumulated the highest amount of Na⁺ andH. jubatum grown in low density on the high salinity site accumulatedthe lowest amount of Na⁺. Soil salinities measured directly from theroot zone were significantly reduced (p<0.05) at the end of thegrowing season when compared to their controls. Atriplex prostrata(high density/low salinity) plots produced the greatest reduction in soilsalinity (15.8%) and S. marina (high density/high salinity) plots hadthe least reduction (1.2%).     

The effect of the bioremediation of soil contaminated with petroleum derivatives on the occurrence of epigeic and edaphic fauna

This field study investigated the colonization process of soil contaminated with different petroleum products (petrol, diesel fuel, spent engine oil; dose: 6000 mg of fuel·kg^?1 dry mass [d.m.] of soil) by epigeic and edaphic invertebrates during the progress of natural bioremediation and bioremediation enhanced using selected microorganisms (ZB-01 biopreparation). Epigeic fauna was captured using pitfall traps. Occurrence of edaphic fauna in soil samples as well as total petroleum hydrocarbon contents (TPH) were also investigated. Results showed that inoculation with ZB-01 biocenosis allowed the degradation of petroleum derivatives in the soil contaminated with diesel fuel and engine oil, with 82.3% and 75.4% efficiency, respectively. Applying bioremediation to all contaminated soils accelerated the process of recolonization by edaphic invertebrates. However, the 28-month period was too short to observe full population recovery in soils contaminated with diesel fuel and engine oil. Microbe-enhanced bioremediation accelerated recolonization by epigeic invertebrates on soil contaminated with diesel fuel, whereas it exerted inhibitory effect on recolonization of soil contaminated with engine oil (especially by Collembola). The observed discrepancies in the rates of recolonization for soils contaminated with petrol and diesel fuel that were still noted at the stage of no longer different TPH levels justify the idea to include the survey of edaphic faunal density as one of the parameters in the ecological risk assessment of various bioremediation techniques.     

The role of soil Phosphorus in differentiation of edaphic ecotypes in Aegilops peregrina

Summary The role of soil Phosphorus (P) availability on the ecotypic differentiation of plants was investigated. Populations of Aegilops peregrina (Hack.) were collected from four habitats which differed in their soil P. The four soils were: Meron (a P-deficient montmorillonitic xerochrept on dolomite), Malkiya (a P-fertile kaolinitic xerochrept on hard limestone), Har-Hurshan and Bet-Guvrin (lithic xerorthents on soft limestone with appreciable amounts of P, mainly as carbonate-apatite).Plants of the four populations were grown in pots with Meron soil which were previously equilibrated with four different amounts of soluble phosphate to give 1.2, 3.1, 10.7 and 18.9 gP g^-1 soil of sodium-bicarbonate extractable P. Plants originated from Malkiya population produced higher dry matter yields than the other three populations. Dry matter yields of the various populations were analyzed by means of a Mitcherlich's response function, versus sodium-bicarbonate extractable (available) soil P. The analysis revealed that Malkiya population plants had a significant advantage over Meron population plants in the response parameter c: this express the response rate of the plants to phosphate by means of dry matter production. With regard to the parameter Po, which represents the ability of plants to utilize barely-available fractions of soil P, the opposite was true. Har-Hurshan and Bet-Guvrin populations were intermediate in these two parameters. A version of the Mitcherlich response function is proposed, which expresses plant yield as a function of both soil available P and plant age.Meron plants contained the highest percentage of P in plant material, but compared to the other populations, they were the most inefficient in producing dry matter from the already absorbed P. Plants from the calcareous soils, Har-Hurshan and Bet-Guvrin, did not show any apparent trend.In soils which contain moderate amounts of lime, P may become a major limiting growth factor. Plant populations became adapted to low availability of P by (1) improving their ability to utilize barely-available soil P fractions and (2), by decreasing their productivity.     

Relationships among microclimate,edaphic conditions,vegetation distribution and soil nitrogen dynamics on the Bogong High Plains,Australia

We examined microclimatic conditions and soil nitrogen (N) dynamics of different alpine plant community types on the Bogong High Plains in Victoria, Australia. Three community types are predominant in the High Plains region, namely grassland, heathland and woodland and together they form so‐called inverted treelines, with grassland in valley floors below the treeline. Outdoor temperature loggers were deployed in the three vegetation types to establish differences among microclimatic conditions. We incubated soils to determine rates of N production and collected additional soil samples for analysis of soil properties and soluble N. Temperature data showed that only grassland communities experienced sub‐zero temperatures in winter. Temperature and soil moisture influenced indices of N mineralization and N nitrification in this alpine ecosystem. Rates of N mineralization were significantly faster than nitrification that only produced consequential amounts of nitrate in summer. This information, together with considerably lower pools of nitrate than ammonium and organic N in the soil, implies that ammonium is the dominant form of soluble N in the ecosystem whereas nitrate most likely only has minor importance for plant nutrition. The results of this study provide insight into ecological processes of this alpine ecosystem and demonstrate the vulnerability of the system to altered climatic and edaphic conditions in the course of climate change.     

Effect of cropping systems on soil chemical characteristics,with emphasis on soil acidification*

The soil under intensive cultivation and low addition of crop residues is exposed to erosion and reduction of organic matter. Increases in soil organic matter, cation exchange capacity (CEC) and nutrient availability may occur in no-till systems with legumes and with large additions of organic residues. Nevertheless, some legumes may increase soil acidification through the carbon and nitrogen cycles. An experiment was carried out over 10 years, with 10 cropping systems on a Dark Red Podzolic soil (Paleudult) to evaluate the effect of no-till cropping systems on soil chemical characteristics. Legume cropping systems resulted in the greatest soil organic C gain and the highest ECEC to a depth of 17.5 cm. The increase was greatest at 0 - 2.5 cm layer. Clover systems resulted in the highest soil acidification at 2.5 - 7.5 and 7.5 - 17.5 cm depths. The rate of soil pH decrease at 2.5 - 7.5 cm depth under clover+ t Spergula/maize system was 0.1 unit year^-1. Differences in soil acidification affected soil ECEC. Soil exchangeable cation data indicate that nitrate leaching increased soil acidification. Maize yields were greatest in legume systems due to increased N supply.     

An investigation of the population ecology of syntopic shrews inhabiting water-cress beds

The population ecology of the shrews Neomys fodiens, Sorex araneus and S. minutus living syntopically in an area of commercial water-cress beds was investigated by live-trapping over a two-year period. The shrew population comprised 52% 5. araneus , 31% N. fodiens and 17% S. minutus. Sorex araneus was the most numerous species in all seasons. Peak numbers of shrews occurred in summer with low numbers in the ensuing winter. Input of new individuals was high, especially of N. fodiens which exceeded 60% in most months. Survival in the study area never exceeded 8 months in N. fodiens and 11 months in S. araneus. Both species suffered approximately 50% mortality and emigration in the first two months of life. Apart from a few, more nomadic, shrews, N. fodiens and S. araneus seemed quite sedentary during trapping periods, moving a mean distance of 13.7 m and 17.2 m between successive captures, respectively. The relatively low numbers of recaptures of N. fodiens at successive trapping periods indicated nomadic behaviour. Both species were more active during darkness than during daylight, and were more active in spring and summer than in winter. High turnover of the shrew population was attributed to mortality and emigration. Emigration was possibly encouraged by competition for space, particularly for nesting sites.     

Influences of soil acidity on Streptomyces populations inhabiting forest soils.

The Streptomyces populations inhabiting five acidic forest soils were examined. It was found that lowering the pH of a medium selective for streptomycetes (starch-casein agar) to the pH of the particular soil horizon being plated influenced both the total numbers and types of streptomycetes that were isolated from the soils examined in this study. On the acidified medium both the numbers of streptomycetes and the percentage of total bacteria on the plates represented by streptomycetes increased (as compared with the same medium with a pH of 7.2). These differences were greatest on the isolations from the most acid soils. The largest concentrations of streptomycetes were found in the surface horizon (0 to 15 cm) and the litter layer immediately over the surface mineral horizon. Acidity tolerance tests demonstrated that random samplings of isolates contained acidophilic, neutrophilic, and acidoduric strains, with the largest numbers of acidophiles being found on the acidified media from the most acid soils. There were no differences between overall utilization of selected carbohydrates among the isolates taken from either the neutral or acidic media, although a larger proportion of the acid media isolates produced acid from the carbohydrates. Evidence is presented which indicates that different types of streptomycetes were isolated on the acid media, and possible reasons for the presence of these acid-tolerant populations are discussed.     

Influences of soil acidity on Streptomyces populations inhabiting forest soils.

The Streptomyces populations inhabiting five acidic forest soils were examined. It was found that lowering the pH of a medium selective for streptomycetes (starch-casein agar) to the pH of the particular soil horizon being plated influenced both the total numbers and types of streptomycetes that were isolated from the soils examined in this study. On the acidified medium both the numbers of streptomycetes and the percentage of total bacteria on the plates represented by streptomycetes increased (as compared with the same medium with a pH of 7.2). These differences were greatest on the isolations from the most acid soils. The largest concentrations of streptomycetes were found in the surface horizon (0 to 15 cm) and the litter layer immediately over the surface mineral horizon. Acidity tolerance tests demonstrated that random samplings of isolates contained acidophilic, neutrophilic, and acidoduric strains, with the largest numbers of acidophiles being found on the acidified media from the most acid soils. There were no differences between overall utilization of selected carbohydrates among the isolates taken from either the neutral or acidic media, although a larger proportion of the acid media isolates produced acid from the carbohydrates. Evidence is presented which indicates that different types of streptomycetes were isolated on the acid media, and possible reasons for the presence of these acid-tolerant populations are discussed.     

Ecology of soil fungi of a sal forest with emphasis on fungistasis

Summary An ecological study of the soil micro-fungi in three forest regions of different age was undertaken. The pH of the soil varied from 6.6 to 6.9. Soil samples were collected from three different depthsviz 0–6, 7–12, and 13–18 inches with aseptic precautions and were studied by a dilution-plate method using peptone-dextrose agar with rose bengal for the fungal analysis. Determinations were made of physico-chemical characters of soil such as organic matter, total nitrogen, phosphorus, water-holding capacity and pH of the soil. The organic matter and nitrogen favoured the growth of fungi in the soil. The upper horizon contained more of the organic matter, nitrogen, phosphorus, and perhaps other elements, which in turn favoured the growth of fungi in soil. The number of fungi decreased according to increase in depth of the soil samples. The frequency and abundance of some dominant fungi have been calculated and the fungal population has been represented both qualitatively and quantitatively. The pattern of colonization of nutrient agar by fungi from soil inocula changed with the increase of concentration of staling products produced by earlier established fungal colonies. At the highest concentration of staling the fungi colonizing the agar disks were species ofTrichoderma, Aspergillus, Penicillium, Curvularia, Alternaria andFusarium. The capacity of species to colonize the staled nutrient medium was due partly to tolerance of the metabolic products diffused in agar disks and partly to density of the population in the inoculated soil. The comparative account of germinated spores on unsterilized and sterilized soil and in controlled condition shows that fungistatic activity is higher in unsterilized soil. In Table 4 the F₃, an oldest soil sample has more fungistatic activity than F₁ and F₂, due to more litter deposition on the floor, which increases the population of micro-organisms and fungistatic activity.     

Zonal plant distribution and edaphic and micrometeorological conditions on a coastal sand dune

Some edaphic and meteorological conditions were examined to detect environmental gradients from shoreline to inland at the Kado-ori coast, Ibaraki, Japan, in 1989. Zonal distribution patterns of coastal dune plant species, including three ubiquitous perennials,Calystegia soldanella, Carex kobomugi andIschaemum anthephoroides, were described in relation to the environmental gradients. Environmental gradients were found in water availability, evaporative demand and soil-water salinity. Water availability, evaluated by thickness of capillary water layer, increased from 10 cm at 20 m to 48 cm at 85 m from the shoreline, reflecting the percentage of fine sand. Evaporative demand, which was evaluated by the evaporation rate from a wet black filter paper, decreased with increasing distance from the shoreline. Soil-water salinity was lowest (15 mmol/L) at 85 m from the shoreline and highest (90 mmol/L) at 30m. On the coast,C. soldanella, a salt-tolerant perennial, was distributed mainly in the environmentally harsh area 40–60 m from the shoreline.Ischaemum anthephoroides andC. kobomugi, less salt-tolerant perennials, occurred mainly 70–80 m from the shoreline, where environmental conditions were more hospitable.