Submitted to: Soil Biology and Biochemistry
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 10/10/1999
Publication Date: N/A
Citation: Ettema, C.H., Lowrance, R.R., Coleman, D.C. 1999. Riparian soil response to surface nitrogen input: the indicator potential of free-living soil nematide populations. Soil Biology and Biochemistry 1625-1638. Interpretive Summary: One of the most important human alterations of global ecological conditions has been the huge increase in available nitrogen (N) introduced into terrestrial and aquatic ecosystems through industrial N fixation for agriculture. Certain ecosystems such as wetlands and riparian zones are known to be effective at trapping N. Much of the trapping ability or ability to act as an N sink is due to uptake of N by vegetation and micro- bial removal of N by denitrification. Unfortunately, long-term enrichment of ecosystems with N may lead to N saturation and a decrease in ability of ecosystems to remove or trap N and thus a decrease in water quality improvement function of the ecosystem. These changes may be manifested through changes in microbial dynamics and microbial biomass in soil of the affected ecosystem. Nematodes are among the most diverse and abundant groups of organisms in soil ecosystems. Because of their abundance and widespread occurrence in soils, a number of programs such as the USEPA Environmental Monitoring and Assessment program have suggested using nematodes as indicators of soil ecosystem health. Part of the assessment of soil ecosystem health involves assessment of effects of long-term, chronic N enrichment. Results from an N addition experiment indicate that nematodes can probably be used as indicators of N enrichment and potential N saturation when combined with other ecosystem measures. These results mean that more tools are available to scientists to assess the long-term changes in terrestrial ecosystems due to human mediated N enrichment.
Technical Abstract: Nitrogen (N) saturation is believed to occur in ecosystems receiving high levels of N loading for long time periods. N saturation of riparian ecosys- tems may lead to nitrate leaching and impacts on water quality. Free-living nematode populations, because of their sensitivity to changing environmental conditions, may provide an early warning sign of N satura- tion. An N addition experiment was conducted to evaluate potential of thes nematodes to act as indicators of N saturation. During 6 months, we measured changes in feeding and life history strategy groups, following single high and repeated low inorganic N-additions to a near stream zone (zone 1) and an upslope area (zone 2) within a riparian forest in the Gulf- Atlantic Coastal Plain of GA. In both cases, N-addition significantly increased the number of bacterivores, but not fungivores. Only bacterivores with r-selected life strategies (high reproduction rate, small body size, short life cycle) increased. Microbivore correlations with microbial data were considerably stronger in N amended treatments than i controls, suggesting that N-addition synchronized microbial-microbivorous dynamics. At the end of experiment, bacterivore abundance returned to control levels, probably partly due to predation, as predator populations had dramatically increased several months after the first N-addition. Increase in predator abundance was greater in single high than repeated low N addition treat- ments, as was the case for bacterivore populations. Results indicate that nematodes can be indicators of N saturation when monitored with other system characteristics such as denitrification rates and litter N.