Emergent properties of ecosystems are a consequence of the synergistic effects of community composition on "ecosystem function" (flux of energy and materials through the ecosystem). The idea that the forest is more than the trees conveys the importance of the concept, but it can be applied broadly to every ecosystem. Species' impacts on turnover rates and productivity have profound effects. As a very simple example, Blair et al. (1990) found that while decomposition rates for mixed litter were similar to the decomposition rates for the litter of tree species incubated individually, there were significant alterations to N flux and abundance of decomposer organisms that could not be predicted based on the patterns detected in incubations of individual litter types. Indeed, one of the most hotly debated and difficult relationships to define is that of the importance of biodiversity to ecosystem function.
There have been a number of hypotheses developed to explain the inherent importance of biodiversity, but few studies have provided convincing support for these hypotheses. Questions such as whether biodiversity impacts characteristics including ecosystem productivity, nutrient retention, and stability have permeated the literature over the past several decades. In an era of decreasing global biodiversity and decreasing genetic diversity, these questions require immediate attention. Intellectually there is no denying that maintaining biodiversity is essential to maintaining the integrity of systems. There are two main problems with this challenge. The first is that measuring the complete biodiversity of a system and determining the degree to which it is in an "undisturbed state" is difficult. Second, biodiversity is not a term that is indicative of quality but quantity. Increasing diversity by increasing undesirable species such as nonnative invasive species will not maintain the integrity of a system, so biodiversity for biodiversity's sake is not the answer. So, what species or how many species should an ecosystem contain? The example above of Blair et al. (1990) suggests that species interactions impact ecosystem function, in this case N flux within a system, which will feed back to impact energy allocation to nutrient acquisition by the plant. Tilman (1996) demonstrated that ecosystem stability increased with aboveground species diversity. However, Klironomos et al. (2000) found that the presence or absence of arbuscular mycorrhizal (AM) fungi significantly changed the relationship of plant diversity to aboveground productivity. Without the fungi, productivity increased as plant species were added to a total of 15 species in a linear fashion. Productivity was maximized at 10 plant species in an asymptotic fashion with AM fungi present. The results suggest that considerations of the importance of diversity in ecosystem function must include an understanding of diversity of all participants, otherwise the importance of diversity among different components may be overlooked. In contrast, the island biogeography study by Wardle et al. (1997) described above found the islands with the greatest aboveground diversity had lower ecosystem process rates. Whether lower rates of nutrient cycling and decomposition are tied to lower belowground diversity remains to be seen.
One of the biodiversity hypotheses examines the degree to which there is functional redundancy in microbial communities. This hypothesis suggests that there are so many species that have the same function that loss of one will not alter the way that the system operates. There are no studies that can provide adequate support for or can eliminate this hypothesis. The amount of stress placed on ecosystems across the globe by anthropogenic influences has changed the way ecosystems operate. Whereas there may have been no impact of the loss of one species from a system before anthropogenic N deposition, this chronic disturbance may have changed the response of the system to the loss of one species. There are two main terms used to characterize the way that an ecosystem responds to a disturbance. While a system that does not change appreciably following a disturbance is said to be resistant, a system that changes but returns to its predisturbance state within a reasonable time frame is said to be resilient. The degree to which ecosystems are resistant or resilient may depend entirely on biodiversity and on the amount of stress currently on the system. Unfortunately, as much as this information is needed to protect ecosystems from degradation and protect species against loss, the stability of ecosystems is an emergent property that cannot easily be measured quantitatively as a parameter or by quantifying one or more of its component parts.
Integrating across scales is a challenge that ecologists have faced for the past hundred years. Scientists that examine microorganisms or soil communities have always dealt with this particular issue. For example, how does one acquire soil samples, in a forest, that are representative of the organisms that live there, in a manner that will allow one to evaluate treatment differences or small-scale rates of change? Conversely, present interpretation of global-scale processes such as net primary productivity and C cycling require very little understanding of micro-bial community dynamics. Processes such as nutrient cycling impact site productivity, but productivity at a global scale can be predicted based on temperature and moisture patterns alone. In models, the microbially mediated steps of nutrient cycling are also predicted by patterns of temperature and moisture. The dilemma facing scientists is that if one considers the component parts of any elemental cycle, the rate that a nutrient becomes available for uptake is dependent on the life cycle of a soil bacteria or the reach of a mycorrhizal companion. In other cases, such as where there is a unique biological interaction (e.g., pathogenesis, mutualism, ecosystem engineering), prediction of population and community dynamics is critical. Failure to investigate the causes and impacts of microbial community structure over the long term will retard our ability to manage ecosystems for the greatest benefit to society and reduce our understanding of the impacts of species loss and global climate change. The role that each organism plays must be examined across spatial scales from molecules to ecosystems, and temporal scales from seconds to centuries, or our ability to predict problems or mitigate damage will be impaired. Integration across scales is a challenge that those that study below-ground systems can begin to facilitate.
The field of science known as ecology is more integrative than most other fields. Ecologists are dependent on specialists that reach across the breadth of the physical sciences. Scientists that study soil microbiology and biochemistry can contribute to and benefit from approaching the medium and organisms they examine as ecologists. Society has placed a great burden on scientists by damaging systems before understanding how they operate. Science is now charged with developing an understanding of these systems and finding ways to mitigate the damage. This can be accomplished only by integrating across scientific fields. As such, this brief introduction to ecology was prepared to stimulate an awareness of the contributions that studies of soils have already made to our understanding of the operation of the natural world and the need to continue to integrate scientific endeavors from molecules to the biosphere.
references and suggested reading
Aber, J. D., and Melillo, J. M. (2001). "Terrestrial Ecosystems." 2nd ed. Academic Press, San Diego.
Alabouvette, C., Lemanceau, P., and Steinberg, C. (1996). Biological control of Fusarium wilts: opportunities for developing a commercial product. In "Principles and Practice of Managing Soilborne Plant Pathogens" (R. Hall, ed.), pp. 192-212. Am. Phytopathol. Soc. Press, St. Paul, MN.
Allen, M. F. (1991). "Ecology of Mycorrhizae." Cambridge Univ. Press, Cambridge, UK.
Allen, M. F., Crisafulli, C., Friese, C. F., and Jeakins, S. L. (1992). Reformation of mycorrhizal symbioses on Mount St. Helens, 1980-1990: interactions of rodents and mycorrhizal fungi. Mycol. Res. 69, 447-453.
Azcon-Aguilar, C., and Barea, J. M. (1992). Interactions between mycorrhizal fungi and other rhizos-phere microorganisms. In "Mycorrhizal Functioning" (M. F. Allen, ed.), pp. 163-198. Chapman & Hall, New York.
Belyea, L. R., and Lancaster, J. (1999). Assembly rules within a contingent ecology. Oikos 86, 402-416.
Bever, J. D. (2003). Soil community feedback and the coexistence of competitors: conceptual frameworks and empirical tests. New Phytol. 157, 465-473.
Blackwood, C. B., and Paul, E. A. (2003). Eubacterial community structure and population size within the soil light fraction, rhizosphere, and heavy fraction of several agricultural systems. Soil Biol. Biochem. 35, 1245-1255.
Blair, J. M., Parmelee, R. W., and Beare, M. H. (1990). Decay rates, nitrogen fluxes and decomposer communities of single and mixed-species foliar litter. Ecology 7, 1976-1985.
Brown, J. H., Stevens, G. C., and Kaufman, D. M. (1996). Geographic range: size, shape, boundaries, and internal structure. Annu. Rev. Ecol. Syst. 27, 597-623.
Brundrett, M. C. (2002). Coevolution of roots and mycorrhizas of land plants. New Phytol. 154, 275-304.
Coleman, D. C., and Crossley, D. A., Jr. (2004). "Fundamentals of Soil Ecology." 2nd ed. Academic Press, San Diego.
Coutinho, H. L. C., Kay, H. E., Manfio, G. P., Neves, M. C. P., Ribeiro, J. R. A., Rumjanek, N. G., and Beringer, J. E. (1999). Molecular evidence for shifts in polysaccharide composition associated with adaptation of soybean Bradyrhizobium strains to the Brazilian Cerrado soils. Environ. Microbiol. 1, 401-408.
Davelos, A. L., Kinkel, L. L., and Samac, D. A. (2004). Spatial variation in frequency and intensity of antibiotic interactions among streptomycetes from prairie soil. Appl. Environ. Microbiol. 70, 1051-1058.
de Jonge, R., Takumi, K., Ritmeester, W. S. and van Leusden, F. M. (2003). The adaptive response of Escherichia coli O157 in an environment with changing pH. J. Appl. Microbiol. 94, 555-560.
del Giorgio, P. A., and Cole, J. J. (1998). Bacterial growth efficiency in natural aquatic systems. Annu. Rev. Ecol. Syst. 29, 503-541.
de Vries, N., Kuipers, E. J., Kramer, N. E., van Vliet, A. H. M., Bijlsma, J. J. E., Kist, M., Bereswill, S., Vandenbroucke-Grauls, C. M. J. E., and Kusters, J. G. (2001). Identification of environmental stress-regulated genes in Helicobacter pylori by a lacZ reporter gene fusion system. Helicobacter 6, 300-309.
Derre, I., Rapoport, G., and Msadek, T. (1999). CtsR, a novel regulator of stress and heat shock response, controls clp and molecular chaperone gene expression in gram-positive bacteria. Mol. Microbiol. 31, 117-131.
Elliott, E. T., Anderson, R. V., Coleman, D. C., and Cole, C. V. (1980). Habitable pore space and micro-bial trophic interactions. Oikos 35, 327-335.
Frey, S. D., Gupta, V. V. S. R., Elliott, E. T., and Paustian, K. (2001). Protozoan grazing affects estimates of carbon utilization efficiency of the soil microbial community. Soil Biol. Biochem. 33, 1759-1768.
Gange, A. C., Brown, V. K., and Sinclair, G. S. (1994). Reduction of lack vine weevil larval growth by vesicular-arbuscular mycorrhizal infection. Entomol. Exp. Appl. 70, 115-119.
Gil, R., Silva, F. J., Zientz, E., Delmotte, F., Gonzalez-Candelas, F., Latorre, A., Rausell, C., Kamerbeek, J., Gadau, J., Hölldobler, B., van Ham, R. C. H. J., Gross, R., and Moya, A. (2003). The genome sequence of Blochmannia floridanus: comparative analysis of reduced genomes. Proc. Natl. Acad. Sci. USA 100, 9388-9393.
Goodwin, S. B., Cohen, B. A., and Fry, W. E. (1994). Panglobal distribution of a single clonal lineage of the Irish potato famine fungus Proc. Natl. Acad. Sci. USA 91, 11591-11595.
Gruber, N., Friedlingstein, P., Field, C. B., Valentini, R., Heimann, M., Richey, J. E., Lankao, P. R., Schulze, E. D., and Chen, C. T. A. (2004). The vulnerability of the carbon cycle in the 21st century: an assessment of carbon-climate-human interactions. In "The Global Carbon Cycle" (C. B. Field and M. R. Raupach, eds.), Vol. 62, pp. 45-76. Island Press, Washington, DC.
Hanski, I., Clobert, J., and Reid, W. (1995). Effect of landscape pattern on competitive interactions. In "Mosaic Landscapes and Ecological Processes" (L. Hansson, L. Fahrig, and G. Merriam, eds.), pp. 203-224. Chapman & Hall, London.
Harrison, S. (1991). Local extinction in a metapopulation context: an empirical evaluation. In "Metapopulation Dynamics: Empirical and Theoretical Investigations" (M. Gilpin and I. Hanski, eds.), pp. 73-88. Academic Press, London.
Hastings, A., Hom, C. L., Ellner, S., Turchin, P., and Godfray, H. C. J. (1993). Chaos in ecology: is Mother Nature a strange attractor? Annu. Rev. Ecol. Syst. 24, 1-33.
Hutchinson, G. E. (1957). Concluding remarks. Cold Spring Harbor Symp. 22, 415-427.
Jenny, H. (1961). Derivation of state factor equations of soils and ecosystems. Soil Sci. Soc. Am. Proc. 25, 385-388.
Jones, C. G., Lawton, J. H., and Shachak, M. (1994). Organisms as ecosystem engineers. Oikos 69, 373-386.
Keddy, P. A. (1992). Assembly and response rules: two goals for predictive community ecology. J. Veg. Sci. 3, 157-164.
Kieft, T. L. (2000). Size matters: dwarf cells in soil and subsurface terrestrial environments. In "Nonculturable Microorganisms in the Environment" (R. R. Colwell and D. J. Grimes, eds.), pp. 19-46. ASM Press, Washington, DC.
Kingsland, S. E. (1991). Defining ecology as a science. In "Foundations of Ecology: Classic Papers with Commentaries" (L. A. Real and J. H. Brown, eds.). Univ. of Chicago Press, Chicago.
Klironomos, J. N., and Hart, M. M. (2001). Food-web dynamics—animal nitrogen swap for plant carbon. Nature 410, 651-652.
Klironomos, J. N., and Kendrick, W. B. (1995). Stimulative effects of arthropods on endomycorrhizas of sugar maple in the presence of decaying litter. Funct. Ecol. 9, 528-536.
Klironomos, J. N., McCune, J., Hart, M., and Neville, J. (2000). The influence of arbuscular mycor-rhizae on the relationship between plant diversity and productivity. Ecol. Lett. 3, 137-141.
Leake, J. R., and Read, D. J. (1997). Mycorrhizal fungi in terrestrial habitats. In "The Mycota," IV, "Environmental and Microbial Relationships" (D. T. Wicklow and B. Sóderstróm, eds.), pp. 281-301. Springer-Verlag, Berlin.
Levins, R. (1969). Some demographic and genetic consequences of environmental heterogeneity for biological control. Bull. Entomol. Soc. Am. 15, 237-240.
Lomolino, M. V. (1999). A species-based, hierarchical model of island biogeography. In "Ecological Assembly Rules: Perspectives, Advances, Retreats" (E. Weiher and P. Keddy, eds.), pp. 272-310. Cambridge Univ. Press, Cambridge, UK.
Lónn, A., Gárdonyi, M., van Zyl, W., Hahn-Hagerdal, B., and Otero, R. C. (2002). Cold adaptation of xylose isomerase from Thermus thermophilus through random PCR mutagenesis gene cloning and protein characterization. Eur. J. Biochem. 269, 157-163.
MacArthur, R. H., and Levins, R. (1967). The limiting similarity, convergence, and divergence of coexisting species. Am. Nat. 101, 377-385.
MacArthur, R. H., and Wilson, E. O. (1967). "The Theory of Island Biogeography." Princeton Univ. Press, Princeton, NJ.
Martinez, N. D., and Dunne, J. A. (1998). Time, space, and beyond: scale issues in food-web research. In "Ecological Scale: Theory and Applications" (D. L. Peterson and V. T. Parker, eds.), pp. 207-226. Columbia Univ. Press, New York.
Molles, M. C. (2002). "Ecology: Concepts and Applications." McGraw-Hill, Boston.
Morin, P. (1999). "Community Ecology." Blackwell Sci., Malden, MA.
Murphy, S. L., and Tate, R. L., III (1996). Bacterial movement through soil. In "Soil Biochemistry" (G. Stotzky and J.-M. Bollag, eds.), Vol. 9, pp. 253-286. Dekker, New York.
Odum, E. (1997). "Ecology: a Bridge between Science and Society." 3rd ed. Sinauer, Sunderland, MA.
Paine, R. T. (1969). A note on trophic complexity and species diversity. Am. Nat. 103, 91-93.
Panikov, N. S. (1995). "Microbial Growth Kinetics." Chapman & Hall, London.
Parker, V. T., and Pickett, S. T. A. (1998). Historical contingency and multiple scales of dynamics within plant communities. In "Ecological Scale: Theory and Applications" (D. I. Peterson and V. T. Parker, eds.), pp. 171-191. Columbia Univ. Press, New York.
Parton, W. J., Schimel, D. S., Cole, C. V., and Ojima, D. S. (1987). Analysis of factors controlling soil organic matter levels in Great Plains grasslands. Soil Sci. Soc. Am. J. 51, 1173-1179.
Paul, E. A., and Clark, F. E. (1996). "Soil Microbiology and Biochemistry." 2nd ed. Academic Press, New York.
Pearl, R., and Reed, L. J. (1920). On the rate of growth of the population of the United States since 1790 and its mathematical representation. Proc. Natl. Acad. Sci. USA 6, 275-288.
Pianka, E. R. (1970). On r- and ^-selection. Am. Nat. 104, 592-597.
Rayner, A. D. M., Beeching, J. R., Crowe, J. D., and Watkins, Z. R. (1999). Defining individual fungal boundaries. In "Structure and Dynamics of Fungal Populations" (J. J. Worrall, ed.), pp. 19-41. Kluwer Academic, Dordrecht.
Real, L. A., and Brown, J. H., eds. (1991). "Foundations of Ecology: Classic Papers with Commentaries." Univ. of Chicago Press, Chicago.
Reznick, D., Bryant, M. J., and Bashey, F. (2002). r- and ^-selection revisited: the role of population regulation in life-history evolution. Ecology 83, 1509-1520.
Robinson, C. H. (2001). Cold adaptation in Arctic and Antarctic fungi. New Phytol. 151, 341-353.
Roeßler, M., and Müller, V. (2001). Osmoadaptation in bacteria and archaea: common principles and differences. Environ. Microb. 3, 743-754.
Rozen, D. E., and Lenski, R. E. (2000). Long-term experimental evolution in Escherichia coli. VIII. Dynamics of a balanced polymorphism. Am. Nat. 155, 24-35.
Schimel, D. S., Enting, I. G., Heimann, M., Wigley, T. M. L., Raynaud, D., Alves, D., and Siegenthaler, U. (1995). CO2 and the carbon cycle. In "Climate Change 1994" (J. T. Houghton, L. G. Meira Filho, J. P. Bruce, H. Lee, B. A. Callander, E. F. Haites, N. Harris, and K. Maskell, eds.), pp. 35-71. Cambridge Univ. Press, Cambridge, UK.
Settembre, E. C., Chittuluru, J. R., Mill, C. P., Kappock, T. J., and Ealick, S. E. (2004). Acidophilic adaptations in the structure of Acetobacter aceti N5-carboxyaminoimidazole ribonucleotide mutase (PurE). Acta Crystallogr. D 60, 1753-1760.
Silva, F. J., Latorre, A., and Moya, A. (2001). Genome size reduction through multiple events of gene disintegration in Buchnera APS. Trends Genet. 17, 615-618.
Six, J., Frey, S. D., Thiet, R. K., and Batten, K. M. (2006). Bacterial and fungal contributions to carbon sequestration in agroecosystems. Soil Sci. Soc. Am. J. 70, 555-569.
Smith, S. E., and Read, D. (1997). "Mycorrhizal Symbiosis." 2nd ed. Academic Press, London.
Staley, J. T. (1997). Biodiversity: are microbial species threatened? Curr. Opin. Biotech. 8, 340-345.
Stubblefield, S. P., and Taylor, T. N. (1988). Recent advances in palaeomycology. New Phytol. 108, 3-25.
Tilman, D. (1982). "Resource Competition and Community Structure." Princeton Univ. Press, Princeton, NJ.
Tilman, D. (1996). Biodiversity: population versus ecosystem stability. Ecology 77, 350-363.
Turchin, P. (1995). Population regulation: old arguments and a new synthesis. In "Population Dynamics: New Approaches and Synthesis" (N. Cappuccino and P. W. Price, eds.), pp. 19-40. Academic Press, San Diego.
Vandermeer, J. H., and Goldberg, D. E. (2003). "Population Ecology: First Principles." Princeton Univ. Press, Princeton, NJ.
Wardle, D. A., Zackrisson, O., Hornberg, G., and Gallet, C. (1997). The influence of island area on ecosystem properties. Science 277, 1296-1299.
Weiher, E., and Keddy, P., eds. (1999). "Ecological Assembly Rules: Perspectives, Advances, Retreats." Cambridge Univ. Press, Cambridge, UK.
Wiens, J. A. (1997). Metapopulation dynamics and landscape ecology. In "Metapopulation Biology: Ecology, Genetics, and Evolution" (I. Hanski and M. E. Gilpin, eds.), pp. 43-61. Academic Press, San Diego.
Wilson, J. B. (1999). Guilds, functional types, and ecological groups. Oikos 86, 507-522.
Woese, C. R. (1994). There must be a prokaryote somewhere: microbiology's search for itself. Microbiol. Rev. 58, 1-9.
Wu, J., and Loucks, O. L. (1995). From balance of nature to hierarchical patch dynamics: a paradigm shift in ecology. Q. Rev. Biol. 70, 439-466.
Wu, X. L., and Conrad, R. (2001). Functional and structural response of a cellulose-degrading methanogenic microbial community to multiple aeration stress at two different temperatures. Environ. Microbiol. 3, 355-362.
Young, J. P. W. (1998). Bacterial evolution and the nature of species. In "Advances in Molecular Ecology" (G. R. Carvalho, ed.). IOS Press, Amsterdam.
Was this article helpful?