科研之友
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摘要
Increased application of nitrogen (N) fertilizers in agricultural systems contributes to significant environmental impacts, including eutrophication of fresh and coastal waters. Rice cutgrass [Leersia oryzoides (L.) Sw.] can significantly enhance denitrification potential in agricultural ditch sediments and potentially reduce N export from agricultural watersheds, but relationships with known drivers are not well understood. To address this, we examined effects of nitrate (NO3-) availability on dinitrogen gas (N-2) and NO(3)(-)fluxes seasonally. Net denitrification rates were measured as positive N-2 fluxes from vegetated intact sediment cores using membrane inlet mass spectrometry (MIMS). We developed Michaelis-Menten models for N-2 fluxes across NO(3)(-)gradients in the spring, summer, and fall seasons. Summer N-2 models exhibited the highest V max (maximum amount of net N-2 flux) and K (concentration of NO(3)(-)in the overlying water at which the net N-2 flux is half of V-max), with a maximum production of N-2 of similar to 20 mg N-2 m(-2) h(-1). Maximum percentage NO(3)(-)retention occurred at 1 mg NO3-L-1 in the overlying water in all seasons, except summer where maximum retention persisted from 1 to 5 mg NO3- L-1. Denitrification rates were strongly correlated with NO(3)(-)uptake by vegetated sediments in spring (r(2) = 0.94, p < 0.0001) and summer (r(2) = 0.97, p < 0.0001), but low NO 3 uptake in fall and winter resulted in virtually no net denitrification during these seasons. Our results indicate that vegetated ditch sediments may act as effective NO3- sinks during the growing season. Ditch sediments vegetated with cutgrass not only immobilized a significant fraction of NO(3)(-)entering them but also permanently removed as much as 30 to 40% of the immobilized NO3- through microbial denitrification.
- 出版日期2017-12
