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Biofilm growth and nitrogen uptake responses to increases in nitrate and ammonium availability

机译：生物膜生长和氮素吸收对硝酸盐和铵盐利用率增加的响应

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Nitrate (NO3 (-)) and ammonium (NH4 (+)) are the two major dissolved inorganic nitrogen (DIN) species available in streams. Human activities increase stream DIN concentrations and modify the NO3 (-):NH4 (+) ratio. However, few studies have examined biofilm responses to enrichment of both DIN species. We examined biofilm responses to variation in ambient concentrations and enrichments in either NO3 (-) or NH4 (+). We incubated nutrient diffusing substrata (NDS) bioassays with three treatments (DIN-free, +NO3 (-) and +NH4 (+)) in five streams. Biomass-specific uptake rates (U (spec) ) of NO3 (-) and NH4 (+) were then measured using in situ additions of N-15-labeled NO3 (-) and NH4 (+). Biomass (estimated from changes in carbon content) and algal accrual rates, as well as U (spec) -NO3 (-) of biofilms in DIN-free treatments varied among the streams in which the NDS had been incubated. Higher ambient DIN concentrations were only correlated with enhanced biofilm growth rates. U (spec) -NO3 (-) was one order of magnitude greater and more variable than U (spec) -NH4 (+), however similar relative preference index (RPI) suggested that biofilms did not show a clear preference for either DIN species. Biofilm growth and DIN uptake in DIN-amended NDS (i.e., +NO3 (-) and +NH4 (+)) were consistently lower than in DIN-free NDS (i.e., control). Lower values in controls with respect to amended NDS were consistently more pronounced for algal accrual rates and U (spec) -NO3 (-) and for the +NH4 (+) than for the +NO3 (-) treatments. In particular, enrichment with NH4 (+) reduced biofilm U (spec) -NO3 (-) uptake, which has important implications for N cycling in high NH4 (+) streams.
机译：硝酸盐（NO3（-））和铵盐（NH4（+））是溪流中可用的两种主要溶解无机氮（DIN）物质。人类活动会增加溪中DIN的浓度并改变NO3（-）：NH4（+）的比例。但是，很少有研究检查生物膜对两种DIN物种富集的反应。我们检查了生物膜对环境浓度变化和NO3（-）或NH4（+）富集的反应。我们将营养扩散基质（NDS）生物测定与五种物流中的三种处理方法（无DIN，+ NO3（-）和+ NH4（+））一起孵育。然后使用原位添加N-15标记的NO3（-）和NH4（+）来测量NO3（-）和NH4（+）的生物量特异性吸收率（U（spec））。在无NDS处理的流中，生物质（通过碳含量的变化估算）和藻类的积累率以及生物膜的U（规格）-NO3（-）在无DIN处理中会有所不同。较高的环境DIN浓度仅与生物膜生长速率提高相关。 U（spec）-NO3（-）比U（spec）-NH4（+）大一个数量级，并且变化更大，但是相似的相对偏爱指数（RPI）表明，生物膜对两种DIN物种均没有明显的偏爱。经过DIN修正的NDS（即+ NO3（-）和+ NH4（+））中的生物膜生长和DIN吸收始终低于不含DIN的NDS（即对照）。相对于+ NO3（-）处理，相对于修正的NDS，藻类应计率和U（规格）-NO3（-）和+ NH4（+）的对照值更低。特别是，富含NH4（+）会减少生物膜U（spec）-NO3（-）的吸收，这对高NH4（+）流中的N循环具有重要意义。

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