Department of Soil and Water Sciences, University of Florida, Gainesville, 32611 FL, USA.
Department of Soil and Water Sciences, University of Florida, Gainesville, 32611 FL, USA.
Water Res. 2016 Dec 1;106:51-61. doi: 10.1016/j.watres.2016.09.048. Epub 2016 Sep 30.
River tributaries are ecologically important environments that function as sinks of inorganic nitrogen. To gain greater insight into the nitrogen cycle (N-cycle) in these environments, the distributions and activities of microbial populations involved in the N-cycle were studied in riparian and stream sediments of the Santa Fe River (SFR) tributaries located in northern Florida, USA. Riparian sediments were characterized by much higher organic matter content, and extracellular enzyme activities, including cellobiohydrolase, β-d-glucosidase, and phenol oxidase than stream sediments. Compared with stream sediments, riparian sediments exhibited significantly higher activities of nitrification, denitrification, dissimilatory nitrate reduction to ammonia (DNRA) and anaerobic ammonia oxidation; correspondingly, with higher copies of amoA (a biomarker for enumerating nitrifiers), nirS and nirK (for denitrifiers), and nrfA (for DNRA bacteria). Among N-cycle processes, denitrification showed the highest activities and the highest concentrations of the corresponding gene (nirK and nirS) copy numbers. In riparian sediments, substantial nitrification activities (6.3 mg-N kg soild average) and numbers of amoA copies (7.3 × 10 copies g soil average) were observed, and nitrification rates correlate with denitrification rates. The guild structures of denitrifiers and nitrifiers in riparian sediments differed significantly from those found in stream sediments, as revealed by analysis of nirS and archaeal amoA sequences. This study shows that riparian sediments serve as sinks for inorganic nitrogen loads from non-point sources of agricultural runoff, with nitrification and denitrification associated with elevated levels of carbon and nitrogen contents and extracellular enzyme activities.
河流支流是生态上重要的环境，它们充当无机氮的汇。为了更深入地了解这些环境中的氮循环（N 循环），本研究对美国佛罗里达州北部圣达菲河（SFR）支流的滨岸和溪流沉积物中的与 N 循环有关的微生物种群的分布和活性进行了研究。滨岸沉积物的有机质含量、胞外酶活性（包括纤维二糖水解酶、β-d-葡萄糖苷酶和酚氧化酶）均明显高于溪流沉积物。与溪流沉积物相比，滨岸沉积物的硝化、反硝化、异化硝酸盐还原为氨（DNRA）和厌氧氨氧化活性显著较高；相应地，氨单加氧酶（amoA，用于计数硝化菌的生物标志物）、nirS 和 nirK（用于反硝化菌）和 nrfA（用于 DNRA 细菌）的拷贝数也较高。在 N 循环过程中，反硝化作用表现出最高的活性和相应基因（nirK 和 nirS）拷贝数的最高浓度。在滨岸沉积物中，观察到大量的硝化活性（平均 6.3mg-N-kg-soild）和 amoA 拷贝数（平均 7.3×10 拷贝-g-土壤），硝化速率与反硝化速率相关。滨岸沉积物中反硝化菌和硝化菌的 guild 结构与溪流沉积物中的 guild 结构明显不同，这是通过 nirS 和古菌 amoA 序列分析揭示的。本研究表明，滨岸沉积物是农业径流非点源无机氮负荷的汇，硝化和反硝化与较高的碳和氮含量以及胞外酶活性有关。
