科研之友
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摘要
Short term nitrogen uptake dynamics in the marshes of the southern Everglades, USA, were determined through implementation of a field mesocosm and isotopic enrichment method. The approach was tested using six mesocosms, three enriched with a 300 parts per thousand (15)N tracer, Ca(NO(3))(2) (+/- 98% (15)N) and three unenriched mesocosms. This (15)N tracer technique allowed the determination of nitrogen fluxes between key ecosystem components. The in situ mesocosm experiment was conducted in a freshwater marl prairie marsh habitat for a period of 21 days. Macrophytes (Cladium jamaicense), periphyton, soil, and consumers (Gambusia holbrooki) were sampled at prescribed intervals to determine the optimal sampling periods necessary to capture peak (15)N tracer uptake. Over the course of the study period, (15)N tracer was detected in all ecosystem components sampled except for soils. Periphyton exhibited the most rapid initial (15)N tracer uptake, with an increase of 3.86 parts per thousand to 7.79 parts per thousand (+/- 1.70) only 5 minutes after tracer addition. Periphyton (15)N signatures continued to increase to 16.49 parts per thousand (+/- 6.45) and 108.15 parts per thousand (+/- 49.40) after 10 minutes and 6 hours, respectively. Increased (15)N signatures were also noted in the macrophyte and consumer components, with peak tracer uptake values occurring in aboveground macrophyte tissue at t = 9 day (26.62 parts per thousand (+/- 5.00)), the belowground macrophyte tissue at t = 15 day (22.01 parts per thousand (+/- 5.83)), and in consumers at t = 15 day (297.09 parts per thousand (+/- 127.36)). Tracer uptake by the soil component was minimal with no significant amount of tracer being detected in any of the three soil layers sampled (0-1, 1-5, and 5-10 cm). This testing of the in situ mesocosm and (15)N isotopic enrichment approach provides a foundation for further experimentation with the method at this and other wetland study sites.
- 出版日期2008-6
