Denitrification and Nitrogen Fixation Dynamics in the Area Surrounding an Individual Ghost Shrimp (Neotrypaea californiensis) Burrow System

Abstract

<jats:title>ABSTRACT</jats:title><jats:p>Bioturbated sediments are thought of as areas of increased denitrification or fixed-nitrogen (N) loss; however, recent studies have suggested that not all N may be lost from these environments, with some N returning to the system via microbial dinitrogen (N<jats:sub>2</jats:sub>) fixation. We investigated denitrification and N<jats:sub>2</jats:sub>fixation in an intertidal lagoon (Catalina Harbor, CA), an environment characterized by bioturbation by thalassinidean shrimp (<jats:named-content content-type="genus-species">Neotrypaea californiensis</jats:named-content>). Field studies were combined with detailed measurements of denitrification and N<jats:sub>2</jats:sub>fixation surrounding a single ghost shrimp burrow system in a narrow aquarium (15 cm by 20 cm by 5 cm). Simultaneous measurements of both activities were performed on samples taken within a 1.5-cm grid for a two-dimensional illustration of their intensity and distribution. These findings were then compared with rate measurements performed on bulk environmental sediment samples collected from the lagoon. Results for the aquarium indicated that both denitrification and N<jats:sub>2</jats:sub>fixation have a patchy distribution surrounding the burrow, with no clear correlation to each other, sediment depth, or distance from the burrow. Field denitrification rates were, on average, lower in a bioturbated region than in a seemingly nonbioturbated region; however, replicates showed very high variability. A comparison of denitrification field results with previously reported N<jats:sub>2</jats:sub>fixation rates from the same lagoon showed that in the nonbioturbated region, depth-integrated (10 cm) denitrification rates were higher than integrated N<jats:sub>2</jats:sub>fixation rates (∼9 to 50 times). In contrast, in the bioturbated sediments, depending on the year and bioturbation intensity, some (∼6.2%) to all of the N lost via denitrification might be accounted for via N<jats:sub>2</jats:sub>fixation.</jats:p>

Temporal and spatial variability of in situ nitrogen fixation activities associated with the Mediterranean seagrass Posidonia oceanica meadows

“…S1) which may depend on the P. oceanica organic photosynthetic exudates. These heterotrophic bacterial N 2 fixers have also been found in Bertics et al (2012) and Gier et al (2016). However, the N 2 -fixing strategies of these organisms need to be further investigated.…”

“…3), implying direct or indirect light dependence of the N 2 -fixing communities in the sediments. N 2 -fixing sulphate-reducing bacteria (SRB) are abundant in a wide range of sediments (Welsh et al 1996(Welsh et al , 1996aBertics et al 2010;Bertics et al 2012;Fulweiler et al 2013;Gier et al 2016), including P. oceanica sediments in Alcanada (Coma 2016). Increased activities of these SRBs during daylight can be due to increased OM availability probably from photosynthetic exudates of microphytobenthic communities (Danovaro 1996) and to temperature changes during the diel cycle (Jørgensen 1994).…”

Profiling gene expression to distinguish the likely active diazotrophs from a sea of genetic potential in marine sediments

“…One of our aims was to determine if the expressed nirS and nifH sequence diversity patterns resembled the unique distribution of denitrifiers and N fixers in Chesapeake Bay, in which the diversity of nirS and nifH decreased along the estuarine gradient from the freshwater end to the more saline mouth (Moisander et al ., ; Bulow et al ., ). N fixation in bare estuarine sediments is recently becoming recognized as an important process occurring in coastal systems (Fulweiler et al ., 2007; 2013; Bertics et al ., 2010; 2012a,b), so for the remainder of the study we focused on quantifying the transcriptional activity of bacterial populations actively expressing nifH . Predominant expressed nifH sequences were used to develop primers and probes for quantitative PCR to follow the changes in abundance, distribution and nifH expression of the microbial groups along the estuarine gradient over an annual temporal cycle.…”

Benthic Dinitrogen Fixation Traversing the Oxygen Minimum Zone Off Mauritania (NW Africa)

“…While bioturbation describes the sediment mixing by benthic organisms, bioirrigation encompasses the exchange of seawater with sediment porewater due to the pumping action of burrowdwelling organisms (Meysman et al, 2006;Kristensen et al, 2012). These processes were associated with increased rates of microbial sulfate reduction (Bertics and Ziebis, 2010) and N 2 fixation (Bertics et al, 2012). Both microbial processes are often coupled in organic-rich sediments (Bertics and Ziebis, 2010;Bertics et al, 2013;Gier et al, 2016).…”

“…Bioturbation and bioirrigation in sediments increase the rate of organic matter supply to subsurface sediment layers, leading to elevated microbial metabolic rates there (Aller and Aller, 1986;Bertics et al, , 2012. While bioturbation describes the sediment mixing by benthic organisms, bioirrigation encompasses the exchange of seawater with sediment porewater due to the pumping action of burrowdwelling organisms (Meysman et al, 2006;Kristensen et al, 2012).…”