摘要
A monitoring program with a weekly sampling frequency over a 15-month period indicates that urea concentrations above a certain threshold level may trigger the blooms of Alexandrium catenella in Thau lagoon. However, urea concentrations were also sometimes related to ammonium and dissolved organic nitrogen concentrations, indicating that the role of urea may not be a direct one. An original approach is used to assess the relative contribution of several nitrogen sources (nitrate, nitrite, ammonium, urea) to growth of A. catenella by comparing nitrogen uptake rates to nitrogen-based growth rates estimated from dilution experiments during four blooms over a 4-year period (2001–2004) in Thau lagoon. Nitrate and nitrite contributed 0.1–14% and 0.1–5% respectively of growth requirements. Ammonium and urea were the main N sources fueling growth of A. catenella (30–100% and 2–59%, respectively). Indirect estimates indicated that an unidentified N source could also contribute significantly to growth at specific times. Concerning ammonium and urea uptake kinetics, half-saturation constants varied between 0.2 and 20 μgat N L−1 for ammonium and between 0.1 and 44 μgat N L−1 over the 4-year period, indicating that A. catenella can have a competitive advantage over other members of the phytoplankton even under low concentrations of ammonium and urea. However, the observed large changes in ammonium and urea uptake kinetics on a short time scale (days) during blooms preclude more precise estimates of those contributions to growth and require further investigation.
摘要译文
在15个月的时间内每周采样频率的toring计划表明尿素浓度高于某一阈值水平可能会引发Thau泻湖的亚历山大藻（Alexandrium catenella）盛开。然而，尿素浓度有时也与铵和溶解的有机氮浓度有关，表明尿素的作用可能不是直接的。最初的方法用于评估几种氮源（硝酸盐，亚硝酸盐，铵，尿素）对A生长的相对贡献。通过比较在Thau泻湖的4年期间（2001-2004）四次大量繁殖期间的稀释实验估算的氮吸收速率和氮基生长速率来进行的catenella。硝酸盐和亚硝酸盐分别占生长要求的0.1-14％和0.1-5％。铵和尿素是促进A. catenella生长的主要N源（分别为30-100％和2-59％）。间接估计表明，未确定的N源也可能在特定时间对增长作出重大贡献。关于铵和尿素吸收动力学，在4年期间，半饱和常数在铵和N L sup -1 / sup之间变化，在N和1 / sup之间变化在0.1和44μg之间，表明A.即使在低浓度的铵和尿素下，catenella也可以比浮游植物的其他成员具有竞争优势。然而，在开花期间短时间内（天）的铵和尿素吸收动力学中保留的大的变化排除了对生长的贡献的更精确估计并且需要进一步研究。
YvesCollos[a];AndréVaquer[a];MohamedLaabir[a];EricAbadie[b];ThierryLaugier[b];AnniePastoureaud[b];PhilippeSouchu[b];. Contribution of several nitrogen sources to growth of Alexandrium catenella during blooms in Thau lagoon, southern France[J]. Harmful Algae, 2007,6(6): 781-789