The effects of salinity and N:P on N-rich toxins by both an N-fixing and non-N-fixing cyanobacteria

Freshwater ecosystems are experiencing increased salinization. Adaptive management of harmful algal blooms (HABs) contribute to eutrophication/salinization interactions through the hydrologic transport of blooms to coastal environments. We examined how nutrients and salinity interact to affect growth, elemental composition, and cyanotoxin production/release in two common HAB genera. Microcystis aeruginosa (non-nitrogen (N)-fixer and microcystin-LR producer; MC-LR) and Aphanizomenon flos-aquae (N-fixer and cylindrospermopsin producer; CYN) were grown in N:phosphorus (N:P) 4 and 50 (by atom) for 21 and 33 days, respectively, then dosed with a salinity gradient (0 – 10.5 g L-1). Both total MC-LR and CYN were correlated with particulate N. We found Microcystis MC-LR production and release was affected by salinity only in the N:P 50 treatment. However, Aphanizomenon CYN production and release was affected by salinity regardless of N availability. Our results highlight how cyanotoxin production and release across the freshwater – marine continuum are controlled by eco-physiological differences between N-acquisition traits.

淡水生态系统正面临日益加剧的盐化问题。有害藻华（Harmful Algal Blooms, HABs）的适应性管理通过藻华的水文输送将其带入沿海环境，进而促进富营养化与盐化的交互效应。本研究探究了营养盐与盐度的交互作用对两种常见有害藻华属物种的生长、元素组成以及氰毒素产生与释放的影响。分别以原子比为4和50的氮磷（N:P）配比培养基培养铜绿微囊藻（Microcystis aeruginosa，非固氮菌，产微囊藻毒素-LR（microcystin-LR, MC-LR））以及水华束丝藻（Aphanizomenon flos-aquae，固氮菌，产柱孢藻毒素（cylindrospermopsin, CYN）），两种藻的培养时长分别为21天和33天，随后施加0至10.5 g·L⁻¹的盐度梯度处理。总MC-LR与总CYN均与颗粒态氮呈显著相关。研究发现，仅在氮磷比为50的处理组中，铜绿微囊藻的MC-LR产生与释放才会受到盐度的调控。然而，水华束丝藻的CYN产生与释放则不受氮素供给条件限制，均会受到盐度的影响。本研究结果揭示了，淡水-海洋连续体中氰毒素的产生与释放过程，是由氮获取性状背后的生态生理差异所调控的。