Ammonium recycling supports toxic Planktothrix blooms in Sandusky Bay, Lake Erie: Evidence from stable isotope and metatranscriptome data
Ammonium recycling supports toxic Planktothrix blooms in Sandusky Bay, Lake Erie: Evidence from stable isotope and metatranscriptome data
复制标题
DOI：
10.1016/j.hal.2018.11.011
复制
发表时间：
2019-01-01
期刊：
影响因子：
6.6
通讯作者：
Newell, Silvia E.
中科院分区：
文献类型：
--
作者：
Hampel, Justyna J.;McCarthy, Mark J.;Newell, Silvia E.
伊利湖的桑达斯基湾接收了来自桑达斯基河的高营养负荷（氮和磷），桑达斯基河是一个农业分水岭。富营养化和蓝藻有害藻华（cyanoHABs）持续整个夏天。浮思蓟是桑达斯基湾的优势生华种和微囊藻毒素的主要产生者。不固定n- 2的蓝藻，如浮游thrix和微囊藻，在化学还原形式的氮上茁壮成长，如铵（NH4+）和尿素。对Sandusky湾铵离子再生、潜在吸收率和微生物群落对NH4+的总需要量进行了定量研究。6 ~ 8月，各站点对光的潜在NH4+吸收率均呈上升趋势。暗吸收率也随季节增加，到8月底，暗吸收率与光吸收率相当。8月的再生率明显高于6月。还比较了桑达斯基湾浮游thrix为主的水华和莫米湾微囊藻为主的水华对铵的吸收动力学。山达斯基湾的半饱和常数（K-m）在6月测得最高，在整个季节中逐渐降低。莫米湾的K-m值在夏初最低，10月上升。7月至8月底，Sandusky Bay的V-max显著增加，反映了对枯竭NH4+的激烈竞争。Sandusky Bay的mettranscriptome结果显示，从初夏的藻青素合成酶（luxury NH4+摄取；cphA1）表达转变为8月的藻青素酶（胞内N动员；cphB/cphA2）表达，支持了微生物群落在夏末氮缺乏的解释。综上所示，在夏末，当氮浓度较低时，Sandusky湾的蓝藻有害藻依赖再生NH4+来支持生长和毒素产生。夏末暗态NH4+吸收增加表明异养对藻圈NH4+耗竭有重要贡献。两个海湾的动力学实验表明，由于浮游thrix对低浓度NH4+具有更高的亲和力，因此在Sandusky湾浮游thrix比微囊藻具有竞争优势。
Sandusky Bay, Lake Erie, receives high nutrient loadings (nitrogen and phosphorus) from the Sandusky River, which drains an agricultural watershed. Eutrophication and cyanobacterial harmful algal blooms (cyanoHABs) persist throughout summer. Planktothrix agardhii is the dominant bloom-forming species and the main producer of microcystins in Sandusky Bay. Non-N-2 fixing cyanobacteria, such as Planktothrix and Microcystis, thrive on chemically reduced forms of nitrogen, such as ammonium (NH4+) and urea. Ammonium regeneration and potential uptake rates and total microbial community demand for NH4+ were quantified in Sandusky Bay. Potential NH4+ uptake rates in the light increased from June to August at all stations. Dark uptake rates also increased seasonally and, by the end of August, were on par with light uptake rates. Regeneration rates followed a similar pattern and were significantly higher in August than June. Ammonium uptake kinetics during a Planktothrix-dominated bloom in Sandusky Bay and a Microcystis-dominated bloom in Maumee Bay were also compared. The highest half saturation constant (K-m) in Sandusky Bay was measured in June and decreased throughout the season. In contrast, K-m values in Maumee Bay were lowest at the beginning of summer and increased in October. A significant increase in V-max in Sandusky Bay was observed between July and the end of August, reflective of intense competition for depleted NH4+. Metatranscriptome results from Sandusky Bay show a shift from cyanophycin synthetase (luxury NH4+ uptake; cphA1) expression in early summer to cyanophycinase (intracellular N mobilization; cphB/cphA2) expression in August, supporting the interpretation that the microbial community is nitrogen-starved in late summer. Combined, our results show that, in late summer, when nitrogen concentrations are low, cyanoHABs in Sandusky Bay rely on regenerated NH4+ to support growth and toxin production. Increased dark NH4+ uptake late in summer suggests an important heterotrophic contribution to NH4+ depletion in the phycosphere. Kinetic experiments in the two bays suggest a competitive advantage for Planktothrix over Microcystis in Sandusky Bay due to its higher affinity for NH4+ at low concentrations.