Abstract：
The effect of rising CO2 levels on cyanobacterial harmful algal blooms (CHABs) is an emerging concern, particularly within eutrophic ecosystems. While elevated pCO2 has been associated with enhanced growth rates of some cyanobacteria, few studies have explored the effect of CO2 and nitrogen availability on diazotrophic (N2-fixing) cyanobacteria that produce cyanotoxins. Here, the effects of elevated CO2 and fixed nitrogen (NO3-) availability on the growth rates, toxin production, and N2 fixation of microcystin, saxitoxin, and anatoxin-a - producing strains of the genus Dolichospermum were quantified. Growth rates of all Dolichospermum spp. were significantly increased by CO2 or both CO2 and NO3- with rates being highest in treatments with the highest levels of CO2 and NO3-for all strains. While NO3- suppressed N2 fixation, diazotrophy significantly increased when NO3--enriched Dolichospermum spp. were supplied with higher CO2 compared to cultures grown under lower CO2 levels. This suggests that diazotrophy will play an increasingly important role in N cycling in CO2-enriched, eutrophic lentic systems. NO3- significantly increased quotas of the N-rich cyanotoxins, microcystin and saxitoxin, at ambient and enriched CO2 levels, respectively. In contrast, elevated CO2 significantly decreased cell quotas of microcystin and saxitoxin, but significantly increased cell quotas of the N-poor cyanotoxin, anatoxin. N2 fixation was significantly negatively and positively correlated with quotas of N-rich and N-poor cyanotoxins, respectively. Findings suggest cellular quotas of N-rich toxins (microcystin and saxitoxin) may be significantly reduced, or cellular quotas of N-poor toxins (anatoxin) may be significantly enhanced, under elevated CO2 conditions during diazotrophic cyanobacterial blooms. Finally, in the future, ecosystems that experience combinations of excessive N loading and CO2 enrichment may become more prone to toxic blooms of Dolichospermum.
摘要：
CO2水平升高对蓝藻有害藻华（CHAB）的影响是一个新兴的问题，特别是在富营养化的生态系统中。虽然pCO2升高与一些蓝细菌的生长速率提高有关，很少有研究探索CO2和氮的有效性对产生氰毒素的重氮营养（固定N2）蓝细菌的影响。这里,升高的CO2和固定氮(NO3-)可用性对生长速率的影响，毒素生产，和微囊藻毒素的N2固定，毒素,并对Dolichospermum属的抗毒素a产生菌株进行了定量。所有Dolichospermum种的生长速率。CO2或CO2和NO3-均显着增加，在所有菌株的CO2和NO3-含量最高的处理中，速率最高。虽然NO3-抑制N2固定，富含NO3的Dolichospermumspp时，重氮营养显着增加。与在较低CO2水平下生长的培养物相比，提供了更高的CO2。这表明重氮营养将在富含CO2的氮循环中发挥越来越重要的作用，富营养化系统。NO3-显著增加了富氮氰基毒素的配额，微囊藻毒素和毒素,在环境和富集的二氧化碳水平下，分别。相比之下,升高的CO2显着降低了微囊藻毒素和毒素的细胞配额，但是显着增加了贫氮的氰基毒素的细胞配额，Anatoxin.N2固定与富氮和贫氮氰基毒素的配额呈显著负相关和正相关，分别。研究结果表明，富含N的毒素（微囊藻毒素和毒素）的细胞配额可能会大大减少，或贫N毒素（anatoxin）的细胞配额可能显着增加，在重氮营养蓝藻水华期间，在升高的CO2条件下。最后,在未来,经历过量氮负荷和CO2富集的组合的生态系统可能更容易出现Dolichospermum的有毒花朵。
