Catálogo de publicaciones - libros

Microorganisms are very small, and their individual effects are equally miniscule. Their effects on ecosystems, however, are felt at the landscape scale. To understand how their aggregate activities are arranged on these landscapes, microbes must be studied at a variety of scales, from the microscopic to the regional, and those scales must eventually be reconciled. Keywords: bacteria, spatial distribution, community analysis, multiscale, interaction scale

This chapter provides a review of the basic statistical techniques used to detect and quantify spatial structure in ecological data as they can be applied to the analysis of microbial communities. It also discusses the general implications of spatial structure in data analysis, including the inappropriate use of parametric statistical tests with spatially autocorrelated data, and suggests possible alternative procedures. Methods discussed include geostatistics and variogram analysis, kriging, correlograms, Mantel and partial Mantel tests, and time-series analysis. Keywords: spatial structure, microbial communities, statistical analysis, autocorrelation, geostatistics, kriging, scale, spatial autocorrelation

There is a growing body of evidence that the spatial distribution of bacteria and their relationships with other soil features play a significant role in the macroscopic function of soil. In the past this has not been widely appreciated, possibly due to the difficulty of studying soils at scales that are relevant to bacterial communities. This paper reviews the evidence for the influence of microscale interactions on function at larger scales and describes recent methodological advances that allow the microscale spatial distribution of bacterial cells and bacterial activities to be quantified. Approaches for integrating the microscale into models of soil function are briefly discussed as are new techniques that have the potential to improve our understanding of microbial – habitat interactions and of how these are linked to soil function. Keywords: bacterial spatial distribution, microscale, microhabitat, scale, biological thin sections, microsampling

After the discovery of the tremendous bacterial diversity in soil at all spatial scales, numerous studies have been motivated by the fact that soil represents a very large reservoir of various genes. Nevertheless, the organization of bacterial cells at the microscale in the soil fabric has been overlooked, although all functional interactions appearing at the ecosystem level initially intervene at the scale of the bacterial cells. Many microbiological processes are based on encounters between cells, and between cells and substrates, between cells and surfaces. This chapter provides insight into the microscale spatial distribution of bacteria in soil, with a special emphasis on the concepts of microcolonies and microhabitats as structuring elements for these patterns. Keywords: bacterial diversity, soil, spatial organization, microscale, microhabitat

Natural populations and habitats are spatially heterogeneous: organisms and the resources they use are not uniformly distributed over space or time, but instead are found in different degrees of aggregation. The rhizosphere, that region of soil surrounding plant roots where microbial activity is influenced by the root, is one of the most microbiologically active habitats on earth. The rhizoplane, the innermost boundary of the rhizosphere, is the surface of the plant root including root hairs, and is a hot spot of plant–microbe activity. Bacteria and fungi on the rhizoplane are favorably positioned to intercept root exudates, and rhizoplane sites are points of root interaction with plant pathoens as well as beneficial microbes.

Terrestrial subsurface environments (below the plow layer) contain an enormous amount of the earth’s biomass, yet are relatively undersampled compared to topsoil, aquatic, and marine environments. Depth emerges as a primary axis for relating distributions of microorganisms and the factors controlling their distribution. There is generally a sharp drop in microbial biomass, diversity, and activity as organic-rich topsoils deepen to mineral-dominated subsoils. Progressively deeper samples from the vadose zone to the capillary fringe and into saturated zones often reveal increases in biomass and changes in dominant microbial populations. Biomass appears to slowly decline with depth, and cell viability is limited by temperature between 4.5 and 6 km. In many subsurface environments, spatial distributions of microorganisms are extremely variable, frequently defying prediction. In a few highly structured saturated environments, such as confined or contaminated shallow aquifers, predominant terminal electron accepting activities are arranged in a spatially ordered manner that is consistent with selected geochemical measurements. Sampling issues specific to subsurface environments still require substantial added effort and expense to achieve a reasonable sample density in comparison to most other environments. Technological advances in microbial assay methodologies are easing some of the methodological boundaries that are often exceeded by subsurface samples. Keywords: aquifer, distribution, microorganism, spatial, subsurface, vadose

Filamentous fungi are unique and significant “spatial integrators” of soil systems. By virtue of their indeterminate and mycelial form, they are able to occupy large volumes of the soil matrix and influence a panoply of soil-based services that underpin the functioning of terrestrial ecosystems. In this chapter, factors which affect the spatial organisation filamentous fungi are described and reviewed at the scale of the hypha, the mycelium, and the community. Environmental factors such as the architecture of the soil and the spatial distribution of nutrient resources play pivotal roles in determining the form and organisation of mycelia. Biotic interactions between fungi and other soil-dwelling organisms further pattern the fungal colonies and the resultant communities. Some of the consequences of such spatial organisation for soil function relate particularly to soil structural dynamics, biotic regulation of plant and microbial communities, and the transport of nutrient elements through the soil system. Keywords: fungi, environmental spatial heterogeneity, biotic interactions, nutrient cycling, nutrient transport, soil

Patchiness of planktonic microorganisms may have important implications in microbial communities not only at small scale within habitats but also at large scales within lake basins and districts in landscapes, and within oceanic regions and biogeographical provinces. However, studies are generally limited to one specific planktonic entity (bacterio-, phyto-, or zooplankton) or one spatial scale and extent (across oceans or freshwater systems, or within systems), and there is still no functional perspective on multiscale patchiness patterns of microbial communities and their generative processes. This review presents some of the key aspects of plankton spatial heterogeneity including concepts, patterns, and processes in the context of a multiscale perspective. The ecological significance of spatial heterogeneity for planktonic microorganisms is presented with a functional perspective relating distribution patterns to environmental processes. The importance of abiotic and biotic forces and that of the biophysical coupling in structuring microbial community in aquatic systems at scales relevant to ecological states or processes of organisms, populations, and ecosystems is discussed. The importance of the application of new and advanced technology, as well as statistical approches is presented and their spatial relevance discussed. Keywords: Spatial heterogeneity, microorganisms, plankton communities, marine and freshwater ecosystems

Recent advances in techniques for investigating soil organisms and evaluating spatial structure have improved our understanding of the spatial dynamics of the soil microbial community. Identifying the scale at which microbial community function and interact in forest soils is essential to designing sampling schemes that will allow us to adequately evaluate the complex relationships between the microbial community and vegetation. Geostatistical tools useful for evaluating these relationships include tools that allow researchers to identify the extent to which the data are spatially structured and allow for the creation of maps for linking organisms and ecosystem characteristics that might exist at different scales. Research on the microbial community in forest soils using these and other scaling techniques has demonstrated that microbial communities both are patterned by and influence the spatial dynamics of the vegetation in their environment at scales that range from centimeter to stand size. Microbes are key to nutrient cycling and microbial community dynamics respond to the vegetation in their immediate vicinity in ways that reflect both the specific identity of the microbe and plant and the spatially patterning of the processes. The mechanisms that underlie these tight relationships of pattern and function reflect the dependence of autotrophs on decomposers and mutualists for nutrient acquisition and the long evolutionary history of these organisms. Improved understanding of the complex spatial relationships between the microbial community and vegetation will improve our ability to provide management guidelines that will allow managers to protect our forest resources. Keywords: forest soils, bacteria, fungi, microorganism, ecosystem function, community structure