Abstract: This study concerns ligninolysis phenomena occurring over 13 months in forest litter. Evergreen oak (Quercus ilex L.) litter was taken as a model because Quercus ilex L. is the most abundant tree species in forests of the French Mediterranean area. Several biotic and abiotic factors potentially involved in transformations of polyphenolic compounds, were measured between October 1997 and October 1998. These factors were: global fungal microflora, the fungi producing phenoloxidases (PO + ), the activities of several phenoloxidases, hydrosoluble phenols, and temperature, humidity and pH of the litter. Results showed that the annual dynamics of fungi and phenoloxidase activities appear to be seasonal, i.e. that these biotic factors such as, were optimal in autumn. A multiple regression analysis showed that there was no correlation between biotic factors such as, fungal populations and phenoloxidase activity and abiotic factors such as, temperature, humidity and pH. Laccases were the preponderant phenoloxidase activities during the year, while those of Mn-peroxidases only appeared in the autumn of 1997. Other phenoloxidases, lignin-peroxidases and tyrosinases were never detected. Interactions between laccases and humic substances were also investigated. Adsorption of laccases on humic substances leads to a shift in the optimal temperature activity of these enzymes from 50 to 308C. Activities of laccases also shifted towards more acidic values when laccases were not adsorbed on humic substances. Nevertheless, the optimal pH was the same (5.7) whether laccases were adsorbed or not to humic substances. Electrophoresis analysis showed little variations in the number of phenoloxidase isoenzymes. Indeed, laccases showed three isoenzymes during the year (Rf 0.23, 0.34 and 0.43). Only one isoform of Mn-peroxidase, with an Rf 0.21, was detected in the litter. 7 2000 Elsevier Science Ltd. All rights reserved.

Abstract: Understanding the processes that underlie larval fish growth are important in predicting recruitment. However, the factors and mechanisms that influence early life stages of fishes are complex and not well understood. We evaluated the role of several abiotic and biotic factors in determining larval fish growth rates across 21 Illinois reservoirs. Larval crappies Pomoxis spp., sunfish Lepomis spp., and gizzard shad Dorosoma cepedianum were collected by push nets from May through July in 1995. Lakes were classified based on morphometric, limnological, and biotic variables using principal components analysis (PCA). In general, the abiotic variables loaded highest in PCA and explained the most variation across reservoirs. The relationships between larval fish growth, using otolith daily rings, were then examined with the principal components and by multiple regression. Larval fish growth rates were highly variable across reservoirs. Mean growth was lowest, but the range of growth rates were highest f...

Abstract: Two types of soil, Haplic Andosols (HA-soil) and Low-humic Andosols (LA-soil), collected from Fukushima in Japan were used to study soil suppressiveness of clubroot disease of Chinese cabbage ( Brassica oleraces ), caused by Plasmodiophora brassicae . Relationships between disease index and concentration of resting spores in both soils, i.e. dose response curves, revealed that LA-soil was more suppressive to the disease than HA-soil. The disease index in LA-soil was significantly lower than that in sterilized LA-soil (SLA-soil) even at 10 6 inoculum concentration, although there was no difference between HA-soil and sterilized HA-soil (SHA-soil) under severe disease pressure. The result suggests that biotic factors in LA-soil are responsible for disease suppression even at a high inoculum level of the pathogen. In addition, the disease index was lower in SLA-soil than in SHA-soil at all inoculum levels, suggesting that abiotic factors were also involved in the suppressiveness of LA-soil. These results indicate that the simultaneous effects of both biotic and abiotic factors are involved in the suppressiveness in LA-soil. The experiment with mixture of sterilized or non-sterilized LA-soils with infested HA-soil indicated that the suppressive factors, i.e. biotic plus abiotic factors, in LA-soil also function even in the soil mixture including HA-soil. The disease index was significantly higher in infested HA-soil diluted with SHA-soil than in infested HA-soil diluted with non-sterilized HA-soil at an inoculum level below estimated 10 3 resting spores g −1 soil. The results suggest that biotic factors play an important role in disease suppression even in conducive HA-soil infested with a low inoculum level of the pathogen.

Abstract: This study was designed to find out which environmental factors (temperature, oxygen concentration and food resources) are more important in steering the rotifers vertical distribution and community structure in an oligo-changing to-mesotrophic reservoir. It was observed that, despite the influence of temperature and oxygen content of the water, biotic factors especially the food availability and changes in trophic state were crucial in shaping the vertical distribution and species composition of rotifers in Meimoa Reservoir, located in Tagus River in Portugal.

Abstract: Microorganisms such as biological control agents (BCA), plant growth-promoting rhizobacteria (PGPR) and yield increasing bacteria (YIB) were introduced along growing roots. The colonization process of introduced bacteria was proved that they attached root tipfirst, then distributed along roots, multiplicated there, and survived as certain population size. The colonization location was closely related with root exudates, which was usually at the junction between cortex cells or at the base of lateral roots or root hairs. The variation of colonization by introduced microorganisms in the rhizosphere was caused by biotic and abiotic factors. Biotic factors included the physiological characters of introduced microorganisms and interactions between introduced microorganisms and native microbes. The more important factors were plant genotypes which associated with introduced beneficial microbes and regulated the population and community of those microbes affecting the colonization of introduced microorganisms. Abiotic factors here referred to soil environmental conditions, e.g., soil texture, water content, soil temperature and pH value.

Abstract: Pneumatophores of the mangrove trees Avicennia marina along the Egyptian Red Sea coast were investigated, to measure the spatial variability in their epiphytic community. Forty eight species of epiphytes (36 algae and 12 invertebrates) were recorded all over the investigated sites. With the resulting data being subjected to comparison indices (Jaccard), the more adjacent sites were the more similar in their biotic contents. This spatial variability is not a geographical trend but it could be attributed to the abiotic and biotic components characteristic to each site.

Abstract: Distribution of the emergent macrophytes Bolboschoenus medianus and Bolboschoenus caldwellii is dominated by the latter at regions higher on the elevation gradient, whereas the former is dominant further down the gradient. Monocultures and mixtures of plants were grown across a water-depth gradient in experimental ponds to determine whether distribution is due to abiotic factors, biotic factors, or a combination of both. Monocultures of each species tolerated exposure, showing little variation in relative growth rate (RGR), net assimilation rate (NAR) or leaf area ratio (LAR). Survival when initially flooded was dependent on shoot height. Plants surviving inundation responded by increasing height through reallocation of biomass. The RGR of B. medianus was maintained across the water-depth gradient by increasing NAR as LAR declined. The RGR of B. caldwellii beyond a depth of −20 cm declined because reductions in LAR were not paralleled by increases in NAR. Mixtures of species growing at 20 cm and 0 cm indicated that biotic interactions occurred and that B. caldwellii was the dominant species. Neither species dominated at −60 cm, presumably because this was beyond the depth tolerated by both species. The study suggests that the zonation of B. medianus and B. caldwellii is attributable to a combination of both abiotic and biotic factors.

Abstract: Droughts and summer drying create unusual temporary aquatic habitats in the form of isolated pools in many small streams around the world. To examine spatial and temporal variation in fish community structure of drying stream pools, their relation to abiotic environmental variables, and associations among species, fish were sampled during summer 1995 and 1996 from pools of four streams in the Ozark mountains, Arkansas, USA. Redundancy analysis of physical-chemical variables showed significant differences among stream sites, but no significant difference between years or stream site by year interaction. Stream sites separated consistently along axes one (habitat heterogeneity) and two (temperature/canopy cover) in both years. Redundancy analysis of fish species-size class densities showed a significant stream site by year interaction. Groupings of stream sites based on fish assemblages were not well explained by physical-chemical variables measured at the pool scale, but were related to location within the drainage basin, and these groupings differed between years. There were 27 (15.8%) and 10 (5.8%) significant associations found among fish species-size classes in 1995 and 1996, respectively, and all but two significant associations in 1995 were positive. Pool depth, habitat heterogeneity, pool size and dissolved oxygen/canopy cover were important local abiotic factors depending on response variables examined. In both years, large fish total density, large central stoneroller density (≥80 mm TL), and small sunfish (<80 mm TL) density were positively related to pool depth. Otherwise, there was no consistent relationship between physical-chemical variables and dependent variables (fish density and species richness) within a year or between years for a given dependent variable. These results support the hypothesis that local abiotic factors are important in structuring fish assemblages in harsh environments, but the importance of those factors varies temporally, and regional influences appear to override local abiotic conditions as factors structuring fish assemblages in drying stream pools. Predation by terrestrial vertebrates may also be an important factor structuring these fish assemblages that has been largely overlooked.

Abstract: The environment of any animal species is a complex set of both abiotic and biotic qualities. Dominant abiotic parameters are light conditions, ambient temperature, relative humidity, precipitation, and wind speed. Biotic components may be classified by the trophic levels at which they occur. On the same trophic level we find conspecifics as mates, as members of a social group, and as competitors. On the same trophic level there are also competitors from other species. Biotic components from different trophic levels are represented by prey, predators, and parasites. The combination of all these factors determines how the world looks for an individual at a specific moment in time.

Abstract: Forest edges are known to consist of microenvironments that may provide habitat for a different suite of species than forest interiors. Several abiotic attributes of the microenvironment may contribute to this change across the edge to center gradient (e.g., light, air temperature, soil moisture, humidity). Biotic components, such as seed dispersal, may also give rise to changes in species composition from forest edge to interior. We predicted that abiotic and biotic measures would correlate with distance from forest edge and would differ among aspects. To test these predictions, we measured abiotic and biotic variables on twelve 175 m transects in each of two 24 ha forest fragments in east-central Illinois that have remained in continuous isolation for upwards of 100 years. Both univariate and multivariate techniques were used to best describe the complex relationships among abiotic factors and between abiotic and biotic factors. Results indicate that microclimatic variables differ in the degree to and distance over which they show an edge effect. Relative humidity shows the widest edge, while light and soil moisture have the steepest gradients. Aspect influences are evidenced by the existence of more pronounced edge effects on south and west edges, except when these edges are protected by adjacent habitat. Edges bordered by agricultural fields have more extreme changes in microclimate than those bordered by trees. According to PCA results, species richness correlates well with microclimatic variation, especially light and soil moisture; however, in many cases species richness had a different depth of edge influence than either of these variables. The herbaceous plant community is heavily dominated by three species. Distributions of individual species as well as changes in plant community composition, estimated with a similarity index, indicate that competition may be influencing the response of the vegetation to the edge to interior gradient. This study indicates that edge effects must be considered when the size and potential buffering habitat of forest preserves are planned.