Latvian Institute of Aquatic Ecology, Agency of Daugavpils University, Voleru Street 4, Riga, Latvia, LV-1007.
FEMS Microbiol Ecol. 2022 Nov 30;98(12). doi: 10.1093/femsec/fiac132.
The semi-enclosed Baltic Sea experiences regular summer blooms of diazotrophic cyanobacteria. Previously, it has been conclusively demonstrated that in open nitrogen-limited parts of the Baltic Sea, cyanobacteria successfully fix atmospheric N2. At the same time, diazotrophic activity is still poorly understood in Baltic Sea sub-regions where nitrogen and phosphorus are co-limiting primary production. To address this gap in research, we used the15 N tracer method for in situ incubations and measured the N2-fixation rate of heterocyst-forming cyanobacteria and picocyanobacteria in the Gulf of Riga, Baltic Sea, from April to September. Physicochemical variables and phytoplankton community composition were also determined. Our results show that the dominant species of cyanobacteria for this region (Aphanizomenon flosaquae) was present in the phytoplankton community during most of the study period. We also establish that the N2-fixation rate has a strong correlation with the proportion of A. flosaquae biomass containing heterocysts (r = 0.80). Our findings highlight the importance of a heterocyst-focused approach for an accurate diazotrophic activity evaluation that is one of the foundations for future management and protection of the Baltic Sea.
半封闭的波罗的海经常出现固氮蓝藻的夏季水华。此前已经明确证明，在波罗的海开阔且氮限制的区域，蓝藻能够成功固定大气中的氮。与此同时，在氮磷共同限制初级生产力的波罗的海亚区，蓝藻的固氮活性仍知之甚少。为了弥补这一研究空白，我们使用 15N 示踪剂方法进行了现场培养，并在波罗的海的里加湾测量了异养固氮蓝藻和微囊藻的固氮速率，时间从四月到九月。还测定了理化变量和浮游植物群落组成。我们的结果表明，对于该地区而言，占优势地位的蓝藻物种（束丝藻）在研究期间的大部分时间里都存在于浮游植物群落中。我们还发现，固氮速率与含有异形胞的束丝藻生物量比例之间存在很强的相关性（r=0.80）。我们的研究结果强调了以异形胞为重点的方法在准确评估固氮活性方面的重要性，这是未来管理和保护波罗的海的基础之一。
