科研之友
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摘要
Stream nutrient uptake and limitation are interconnected by relationships between nutrient supply and demand. We used multiple approaches, including estimates of nutrient supply, measures of stream metabolism derived from dissolved O-2 curves, and nutrient-enrichment experiments, as complementary measures of nutrient supply, demand, and limitation in New Hope Creek, a 3r d -order stream in the Duke Forest of North Carolina. Over the course of 1 y of sampling, NO3- N supply relative to demand (S:D) was large during winter (S:D = 133.4), spring (S:D = 62.0), and summer (S:D = 108.32). Potential N demand, estimated based on ecosystem metabolic rates, was measurable during winter, spring, and summer months, but we measured no N uptake in response to N addition from nutrient-enrichment experiments. In contrast, during autumn, declines in stream NO3- N concentrations to annual minima (autumn concentration range 0.009-0.034 mg/L NO3- N), and low S:D (1.84) induced transient N limitation, and NO3- N enrichment stimulated increased uptake. We demonstrate that nutrient-enrichment experiments fail to detect uptake when nutrient concentrations are nonlimiting even when ambient biological uptake remains an important sink for the nutrient of interest. In addition, we present a conceptual model of 'supply-demand space' to aid interpretation of nutrient-enrichment data. Last, we suggest that simultaneous measures of nutrient supply, demand, uptake, and limitation can help define supply-demand relationships and provide a step toward a more robust understanding of biogeochemical cycling in streams.
- 出版日期2018-9
