Ecosystem, grassland

Evidence suggests that structure and function are intimately related, but the precise nature of the relationship remains to be fully elucidated. Although some research clearly shows that structure responds before function to perturbation, other evidence indicates that the functional group component of an ecosystem (grassland and plant systems) may be a greater determinant of ecosystem processes than the species component of diversity (Tilman et al. 1996,1997). They conducted experiments in which species diversity (number of plant species), functional diversity (number of functional groups), and functional composition (different combinations of functional groups) of various plant species were manipulated in experimental field plots (Tilman et al. 1996, 1997). They found that the number of functionally different... 

Fig. 11. Forage production of grassland ecosystems subject to initial overgrazing (early 20th century, degree of production estimated) and subsequent invasion by the alien grass, Eragrostis lehmanniana (after Morton, 1985).

Kuperman, R.G. and Carreiro, M.M., Soil heavy metal concentrations, microbial biomass and enzyme activities in a contaminated grassland ecosystem, Soil Biol Biochem, 29 (2), 179-190, 1997. 

Loiseau P, Soussana JF (1999) Elevated [C02], temperature increase and N supply effects on the turnover of below-ground carbon in a temperate grassland ecosystem. Plant Soil 210 233-247... 

Grassland ecosystem On a revegetated mine tailings dam Soil (1-8 cm depth) 1915-2160 DW 106... 

Andrews, S.M., M.S. Johnson, and J.A. Cooke. 1989. Distribution of trace element pollutants in a contaminated grassland ecosystem established on metalliferous fluorspar tailings. 2 zinc. Environ. Pollut. 59A 241-252. 

Bardgett RD, Shine A (1999) Linkages between plant litter diversity, soil microbial biomass and ecosystem function in temperate grasslands. Soil Biol Biochem 31 317-321... 

With respect to soils, a receptor is thus characterized as a specific combination of land use (e g., Forest ecosystem types, agricultural crops) and soil type. The critical loads can be calculated for both agricultural soils (grassland, arable land) with HM inputs with deposition, fertilizers, and wastes, and non-agricultural (forest and steppe) soils, where atmospheric deposition is the only input to the system. 

Possible effects on soil hfe, plants (phytotoxicity) and on ground water are of concern in all types of ecosystems. Food quality criteria are, however, of relevance for arable land only, whereas possible secondary poisoning effects on domestic animals or terrestrial fauna are relevant in grassland and non-agricultural land. A final critical limit can be based on the most sensitive receptor. Even though effects vary for each metal, soil microbes and soil fauna are generally most sensitive. 

The receptors of interest are soils of agricultural (arable lands, grasslands) and non-agricultural (forests, steppes, heath lands, savanna, etc.) ecosystems. In non-agricultural ecosystems, the atmospheric deposition is the only input of heavy metals. Regarding the Forest ecosystems, a distinction should at least be made between Coniferous and Deciduous Forest ecosystems. When detailed information on the areal distribution of various tree species (e.g., pine, fir, spruce, oak, beech and birch) is available, this should be used since tree species influence the deposition and uptake of heavy metals and the precipitation excess. On a world scale, soil types can be best distinguished on the basis of the FAO-UNESCO Soil Map of the World, climate and ecosystem data from NASA database (1989). 

Variable geographical conditions and distribution of emission source causes highly uneven distribution of ecosystem-specific deposition patterns across Europe. From the viewpoint of the adverse effects it appears that the most interesting ecosystems are forests, arable lands, grasslands, and freshwaters. In Figure 19 depositions of cadmium to forests and to arable lands are exemplified. As seen, in areas where there are both forests and arable lands, deposition fluxes to forests are substantially higher than to arable lands. 

Miethling R et al (2000) Variation of microbial rhizosphere communities in response to crop species, soil origin, and inoculation with Sinorhizobium meliloti L33. Microb Ecol 40 43 Gray ston S J et al (2001) Accounting for variabUity in soU microbial communities of temperate upland grassland ecosystems. SoU Biol Biochem 33 533... 

Tropical rain forest, grassland and savanna, scrub and deciduous forest The tropics and subtropics are comprised within 30° of latitude on both sides of the equator. Various ecosystems are represented the tropical rain forest (Jacobs 1981), grassland and savanna, scrub and deciduous forest, and arid land (AY 1979) (Fig. 6.1). 

The tropical ecosystem called grassland and savanna is found in the southern American continent (particularly northern Colombia, Bolivia, and central Brazil) and most extensively in Africa (from just below the Sahara to the Cape Province). In the East it is limited to northern Australia. 

Steenwerth, K.L., Jackson, L.E., Calderon, F.J., Stromberg, M.R. and Scow, K.M. 2003. Soil microbial community composition and land use history in cultivated and grassland ecosystems of coastal California. Soil Biology and Biochemistry 35(3) 489-500. 

Natural disturbance patterns can be very important when evaluating the likelihood of recovery from anthropogenic stressors. Ecosystems that have been subjected to repeated natural disturbances may be more vulnerable to anthropogenic stressors (e.g., overfishing). Alternatively, if an ecosystem has become adapted to a disturbance pattern, it may be affected when the disturbance is removed (fire-maintained grasslands). The lack of natural analogues makes it difficult to predict recovery from novel anthropogenic stressors such as exposure to synthetic chemicals. 

Figure 6.1. Ecosystem area and soil carbon content to 3-m depth. Lower Panel Global areal extent of major ecosystems, transformed by land use in yellow, untransformed in purple. Data from Hassan et al. (2005) except for Mediterranean-climate ecosystems transformation impact is from Myers et al. (2000) and ocean surface area is from Hassan et al. (2005). Upper Panel Total C stores in plant biomass, soil, yedoma/permafrost. D, deserts G S(tr), tropical grasslands and savannas G(te), temperate grasslands ME, Mediterranean ecosystems F(tr), tropical forests F(te), temperate forests F(b), boreal forests T, tundra FW, freshwater lakes and wetlands C, croplands O, oceans. Data are from Sabine et al. (2004), except C content of yedoma permafrost and permafrost (hght blue columns, left and right, respectively Zimov et al., 2006), and ocean organic C content (dissolved plus particulate organic Denman et al., 2007). This figure considers soil C to 3-m depth (Jobbagy and Jackson, 2000). Approximate carbon content of the atmosphere is indicated by the dotted lines for last glacial maximum (LGM), pre-industrial (P-IND) and current (about 2000). Reprinted from Fischlin et al. (2007) in IPCC (2007). See color insert.

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