Bartoli Marco, Nizzoli Daniele, Zilius Mindaugas, Bresciani Mariano, Pusceddu Antonio, Bianchelli Silvia, Sundbäck Kristina, Razinkovas-Baziukas Arturas, Viaroli Pierluigi
Department of Chemistry, Life Sciences and Environmental Sustainability, University of Parma, Parma, Italy.
Marine Research Institute, University of Klaipeda, Klaipeda, Lithuania.
Front Microbiol. 2021 Jan 21;11:612700. doi: 10.3389/fmicb.2020.612700. eCollection 2020.
The interaction between microbial communities and benthic algae as nitrogen (N) regulators in poorly illuminated sediments is scarcely investigated in the literature. The role of sediments as sources or sinks of N was analyzed in spring and summer in sandy and muddy sediments in a turbid freshwater estuary, the Curonian Lagoon, Lithuania. Seasonality in this ecosystem is strongly marked by phytoplankton community succession with diatoms dominating in spring and cyanobacteria dominating in summer. Fluxes of dissolved gas and inorganic N and rates of denitrification of water column nitrate (D) and of nitrate produced by nitrification (D) and sedimentary features, including the macromolecular quality of organic matter (OM), were measured. Shallow/sandy sites had benthic diatoms, while at deep/muddy sites, settled pelagic microalgae were found. The OM in surface sediments was always higher at muddy than at sandy sites, and biochemical analyses revealed that at muddy sites the OM nutritional value changed seasonally. In spring, sandy sediments were net autotrophic and retained N, while muddy sediments were net heterotrophic and displayed higher rates of denitrification, mostly sustained by D. In summer, benthic oxygen demand increased dramatically, whereas denitrification, mostly sustained by D, decreased in muddy and remained unchanged in sandy sediments. The ratio between denitrification and oxygen demand was significantly lower in sandy compared with muddy sediments and in summer compared with spring. Muddy sediments displayed seasonally distinct biochemical composition with a larger fraction of lipids coinciding with cyanobacteria blooms and a seasonal switch from inorganic N sink to source. Sandy sediments had similar composition in both seasons and retained inorganic N also in summer. Nitrogen uptake by microphytobenthos at sandy sites always exceeded the amount loss denitrification, and benthic diatoms appeared to inhibit denitrification, even in the dark and under conditions of elevated N availability. In spring, denitrification attenuated N delivery from the estuary to the coastal area by nearly 35%. In summer, denitrification was comparable (~100%) with the much lower N export from the watershed, but N loss was probably offset by large rates of N-fixation.
微生物群落与底栖藻类在光照不足的沉积物中作为氮(N)调节剂的相互作用在文献中鲜有研究。在立陶宛的库尔斯沙嘴泻湖这个浑浊的淡水河口,对春季和夏季沙质和泥质沉积物中沉积物作为氮源或氮汇的作用进行了分析。该生态系统的季节性特征强烈地表现为浮游植物群落演替,春季以硅藻为主,夏季以蓝藻为主。测量了溶解气体和无机氮通量、水柱硝酸盐反硝化速率(D)以及硝化作用产生的硝酸盐反硝化速率(D)和沉积特征,包括有机物质(OM)的大分子质量。浅/沙质站点有底栖硅藻,而在深/泥质站点发现有沉降的浮游微藻。表层沉积物中的有机物质在泥质站点总是高于沙质站点,生化分析表明,在泥质站点,有机物质的营养价值随季节变化。春季,沙质沉积物是净自养的并保留氮,而泥质沉积物是净异养的且反硝化速率较高,主要由D维持。夏季,底栖需氧量急剧增加,而在泥质沉积物中主要由D维持的反硝化作用减少,在沙质沉积物中保持不变。与泥质沉积物相比,沙质沉积物中反硝化作用与需氧量的比率显著较低,与春季相比,夏季也是如此。泥质沉积物显示出季节性明显不同的生化组成,脂质比例较大,与蓝藻水华同时出现,并且季节性地从无机氮汇转变为氮源。沙质沉积物在两个季节的组成相似,夏季也保留无机氮。沙质站点微型底栖植物的氮吸收量总是超过反硝化作用损失的量,并且底栖硅藻似乎抑制反硝化作用,即使在黑暗和高氮可用性条件下也是如此。春季,反硝化作用使从河口向沿海地区的氮输送减少了近35%。夏季,反硝化作用与流域低得多的氮输出相当(约100%),但氮损失可能被大量的固氮作用抵消。