Kerner M., Spitzy A.
Institute for Hydrobiology and Fishery Science, University of Hamburg, Zeiseweg 9, 22765 Hamburg, Germany.
Microb Ecol. 2001 Jan;41(1):69-81. doi: 10.1007/s002480000031.
Bacterial conversion of high (HMW > 3,000 Da) and low (LMW < 3,000 Da) molecular weight DON (dissolved organic nitrogen) was studied along the freshwater section of the Elbe estuary during the summer of 1997. Indigenous populations of picoplankton were incubated in a flow-through chamber that allowed a constant exchange of sterile, filtered Elbe water as the culture medium for the microorganisms, which remained within the chamber. Nitrogen conversion was followed by changes in the concentrations of total and low molecular weight DON and dissolved inorganic nitrogen compounds, the uptake of O2, and bacterial growth. Along the Elbe estuary, total DON concentrations varied between 0.69 and 1.1 mg N L-1, of which between 64 and 79% was LMW-DON. Ammonium was a minor nutrient present in the Elbe at concentrations below 0.26 mg N L-1. During incubation in the laboratory between 27 and 64% of the LMW-DON was consumed at rates ranging from 24 to 51 µg N L-1 h-1. HMW-DON was used only when the degradable LMW-DON pool became exhausted and accounted for between 60 and 100% of the HMW-DON. This produced an increase in the DON consumption rate between 43 and 79 µg N L-1 h-1. Nitrification rates were independent of the external ammonium concentration until it decreased to below 1 µg N-NH4 L-1. Most of the N in the nitrification process originated as NH4 regenerated from DON. Between 75 and 100% of the LMW-DON and ammonium consumed was rapidly converted to nitrate. This amount decreased to between 65 and 85% when HMW-DON was consumed in addition to the LMW-DON. DON and ammonium consumption supported nitrification rates up to 71 µg N L-1 h-1. The amount of DOC (dissolved organic carbon) degraded was not equivalent to the C:N ratio of the total dissolved organic matter. Calculations based on oxygen consumption for respiration and ammonium regeneration revealed that the substrates used during the incubations contained C:N at ratios of about 3:1. These results suggest that the nitrogen-rich compounds had been removed from the dissolved organic matter and subsequently consumed by bacteria, while the carbon skeleton remained mostly unaffected by the degradation processes.
1997年夏季，对易北河河口淡水段中高分子量（HMW > 3,000 Da）和低分子量（LMW < 3,000 Da）溶解有机氮（DON）的细菌转化进行了研究。微微型浮游生物的本地种群在一个流通式培养室中进行培养，该培养室允许无菌、经过滤的易北河水作为微生物的培养基不断交换，微生物则留在培养室内。通过总DON和低分子量DON以及溶解无机氮化合物浓度的变化、氧气的吸收和细菌生长来跟踪氮的转化。在易北河河口，总DON浓度在0.69至1.1 mg N L-1之间变化，其中64%至79%为低分子量DON。铵是易北河中含量较少的养分，浓度低于0.26 mg N L-1。在实验室培养期间，27%至64%的低分子量DON被消耗，消耗速率在24至51 µg N L-1 h-1之间。只有当可降解的低分子量DON库耗尽时，高分子量DON才会被利用，且占高分子量DON的60%至100%。这使得DON消耗速率增加到43至79 µg N L-1 h-1之间。硝化速率与外部铵浓度无关，直到其降至低于1 µg N-NH4 L-1。硝化过程中大部分氮源自从DON再生的NH4。75%至100%的低分子量DON和消耗的铵迅速转化为硝酸盐。当除了低分子量DON还消耗高分子量DON时，这一比例降至65%至85%之间。DON和铵的消耗支持了高达71 µg N L-1 h-1的硝化速率。降解的溶解有机碳（DOC）量与总溶解有机物的C:N比不相等。基于呼吸耗氧量和铵再生的计算表明，培养期间使用的底物C:N比约为3:1。这些结果表明，富氮化合物已从溶解有机物中去除，随后被细菌消耗，而碳骨架在降解过程中大多未受影响。
