| Popis: |
Human activities involved with urban development have substantial impact on soil. This work examined anthropogenic influences measured by changes in soil profile, length of urbanization period, and the distance from paved roads on soil ecosystems, specifically on the size of key soil nutrient pools, and the abundance and diversity of soilborne nitrogen fixing bacteria and soil nematodes. Further spatial organization of the urban soil nematode community was described at functional guild and taxonomic level to explore ways to improve the value of nematodes as bioindicators. First, experimental plots with four different soil matrixes which are commonly found in newly developed urban sites (topsoil, compost amended topsoil, subsoil and compost amended subsoil) were established. The abundance and diversity of soilborne nitrogen fixing bacteria using gene marker, nifH were monitored for one-year period after tall fescue lawn establishment. Initially, abundance of nifH measured by quantitative polymerase chain reaction was significantly lower in subsoil compared to topsoil, but it enriched quickly to the level in topsoil over a one year period. However, the composition of nifH differed between topsoil and subsoil plots. Second, the sizes of key soil nutrient pools were measured and compared along temporal and spatial gradients related to urban development. Study sites were selected from same land use type; turfgrass-covered soils in public schools. Total soil carbon, nitrogen, organic matter, pH, and exchangeable Ca varied in a predictable manner with duration of urbanization and distance from paved roads. To evaluate the potential of soil nematodes as indicators for detecting differences in urban soil chemistry, soil nematodes were extracted, counted, and identified to the genus level. Along the urbanization duration gradient, soil nematode abundance and diversity indices clearly reflected differences in soil chemistry. The abundance of soil nematodes in road-side soils was lower, in spite of higher quantity of total carbon and nitrogen compared to interior soils suggesting that soil processes such as decomposition and mineralization may have been suppressed in road-side soils. However, none of the soil nematode community indices, which measure proportions of functional guilds reflected altered urban soil chemical properties. To explore ways to improve the soil nematode community index system, spatial organization of urban soil nematodes was assessed at the genus, trophic group, colonizer-persister class, and functional guild levels using the aggregation index, ‘b’ from Taylor’s power law. Overall, soil nematodes tended to aggregate more at the functional group level than at the genus level. The colonizer-persister scale, which reflects life strategy traits of nematodes, was related to the parameter b; colonizers with higher fecundity and smaller body size aggregated more than persisters with low fecundity and larger body size. |
