Microfauna

Abstract: The paper describes the ecosystem constituted by marine sediments and their microfiora and fauna but with special emphasis on the ecology of ciliated protozoa. This description is based on quantitative studies of the vertical and horizontal distribution of the fauna, the physicochemical factors (O2, H2, S, Eh, pH, grain size, organic matter, salinity) and the microfiora, and on model experiments with artificial and natural sediments. Factors controlling the oxidation-reduction properties of sediments, the O2-uptake of reduced sediments and the respiration and photosynthesis of undisturbed sediments were studied. Among other things it is demonstrated that the microfaunal communities can be correlated with the oxidation-reduction properties of sediments and with their mechanical composition and that the endproducts of anaerobic decomposition (notably H2S) are of large trophic significance to the sediment ecosystem through the activity of cherno- and photoautotrophic bacteria. The energetic role of ...

Abstract: Global environmental changes are expected to impact the abundance of plants and animals aboveground, but comparably little is known about the responses of belowground organisms. Using meta-analysis, we synthe- sized results from over 75 manipulative experiments in order to test for patterns in the effects of elevated CO2, warming, and altered precipitation on the abundance of soil biota related to taxonomy, body size, feeding habits, eco- system type, local climate, treatment magnitude and duration, and greenhouse CO2 enrichment. We found that the positive effect size of elevated CO2 on the abundance of soil biota diminished with time, whereas the negative effect size of warming and positive effect size of precipi- tation intensified with time. Trophic group, body size, and experimental approaches best explained the responses of soil biota to elevated CO2, whereas local climate and ecosystem type best explained responses to warming and altered precipitation. The abundance of microflora and microfauna, and particularly detritivores, increased with elevated CO2, indicative of microbial C limitation under ambient CO2. However, the effects of CO2 were smaller in field studies than in greenhouse studies and were not sig- nificant for higher trophic levels. Effects of warming did not depend on taxon or body size, but reduced abundances were more likely to occur at the colder and drier sites. Precipitation limited all taxa and trophic groups, particu- larly in forest ecosystems. Our meta-analysis suggests that the responses of soil biota to global change are predictable and unique for each global change factor.

Abstract: Much of the work regarding earthworm effects on other organisms has focused on the functional significance of microbial-earthworm interactions, and little is known on the effects of earthworms on microfloral and faunal diversity. Earthworms can affect soil microflora and fauna populations directly and indirectly by three main mechanisms: (1) comminution, burrowing and casting; (2) grazing; (3) dispersal. These activities change the soil's physico-chemical and biological status and may cause drastic shifts in the density, diversity, structure and activity of microbial and faunal communities within the drilosphere. Certain organisms and species may be enhanced, reduced or not be affected at all depending on their ability to adapt to the particular conditions of different earthworm drilospheres. A large host of factors (including CaCO3, enzymes, mucus and antimicrobial substances) influence the ability of preferentially or randomly ingested organisms to survive (or not) passage through the earthworm gut, and their resultant capacity to recover and proliferate (or not) in earthworm casts. Small organisms, particularly microflora and microfauna, with limited ability to move within the soil, may benefit from the (comparatively) long ranging movements of earthworms. Microflora and smaller fauna appear to be particularly sensitive to earthworm activities, and priming effects enhancing nutrient release, particularly in casts, are common. Larger fauna such as microarthropods, enchytraeids and Isopods may be enhanced under some conditions (e.g., in earthworm middens), but in other cases earthworm activity may lead to a decrease in their populations due to competition for food (microbes and organic materials), and spatial and temporal changes in food abundance. Nevertheless, considering the presently available data, the beneficial interactions of earthworms and microflora and fauna appear to far outweigh the potential negative effects. However, much is still unknown regarding the interactions of earthworms of different ecological categories on the diversity and function of microfloral and faunal communities, and much more interdisciplinary research is needed to assess the potential role of earthworms in regulating the diversity of microflora and fauna in soil systems and the potentially beneficial or harmful effects this regulation may have on ecosystem function and plant growth in different ecosystems.