Benthic N pathways in illuminated and bioturbated sediments studied with network analysis

Abstract

The regulation of benthic nitrogen (N) cycling by multiple interactions among bacteria, macrofauna, and primary producers is poorly understood. We hypothesized that a biodiverse benthic system should better exploit the benthic N‐availability and retain N than a simpler one. Retention occurs by avoiding losses both to the water column via increased recycling and to the atmosphere via decreased N2 fluxes and by limiting energy‐costly processes as N‐fixation. We also hypothesized that primary producer‐bacterial competition is reduced in the presence of macrofauna due to mobilization of refractory N pools. To this purpose, the effects of two bioturbators (the detritivorous Sparganophilus tamesis and the filter‐feeding Corbicula spp.) and two primary producer growth forms (the rooted macrophyte Vallisneria spiralis and microphytobenthos) on benthic N cycling were studied. An array of N‐processes were measured along a complexity gradient (from bare sediments to all combinations of the above mentioned organisms), and experimental outcomes were analyzed via ecological network analysis (ENA). This suite of algorithms, applied to the microscale, revealed differential partitioning of N fluxes among bare sediments (highest denitrification rates), sediments with macrofauna (highest recycling), and sediments with rooted plants (highest N‐fixation). N2 losses and inputs were significantly reduced when all components were represented, and N requirements by primary producers were to a large extent supported by the activity of macrofauna. Ecological interactions in biodiverse benthic systems promoted an efficient exploitation of sedimentary N pools, increased the coupling between recycling and uptake, and maximized N use efficiency at the expenses of losses and imports.

Application of the isotope pairing technique in sediments: Use, challenges, and new directions

“…The potential for N 2 : Ar to be used in combination with IPT may be of benefit when working in shallow environments where plants, meio‐ and macrofaunal activity creates heterogeneous sediments, and therefore IPT assumptions could be invalid or too complex to be determined with a single method (Magri et al ). In previous studies, N 2 : Ar has been shown to overestimate N 2 production in permeable sediments under advective pore‐water flow (Cook et al ), underestimated N 2 production in sediments reworked by macrofauna (Ferguson and Eyre ) and in estuarine sediments with hypoxic bottom water (Crowe et al ), and give comparable results (Eyre et al ; Deek et al ) relative to whole‐core‐IPT measurements.…”

“…However, to date anammox has not been shown to be a significant process in sediments in which the impacts of bioturbation have been investigated (Bonaglia et al , ) and very few studies have been carried out on how bioturbation may impact benthic N‐fixation (Bertics et al ). As such the presence of benthic animals and their burrowing activities may produce as yet unknown antagonistic or synergistic effects on benthic N cycling processes (Magri et al ).…”

“…As such the presence of benthic animals and their burrowing activities may produce as yet unknown antagonistic or synergistic effects on benthic N cycling processes (Magri et al 2018). The presence of burrowing fauna causes issues in the application of the whole-core IPT.…”

Estuarine Macrofauna Affects Benthic Biogeochemistry in a Hypertrophic Lagoon

“…Nevertheless, species that seem redundant under natural conditions may be important for ecosystem functioning when ecosystems are disturbed [10]. The understanding of the biogeochemical dynamics in environments characterized by high biodiversity is strongly limited by the complex and multiple interactions among species [11]. In strongly anthropized environments, generally associated with a strong loss of biodiversity, identification of important ecological niches is even more difficult.…”

Spatial heterogeneity and short‐term oxygen dynamics in the rhizosphere of Vallisneria spiralis: Implications for nutrient cycling

“…free sulfides and metal ions) around and within the roots, where they otherwise may induce physiological stress and damage to the plant (Geurts et al, 2009;Koch & Mendelssohn, 1989). In addition, ROL may promote aerobic microbial processes that mobilise nutrients and trace-elements from recalcitrant organic matter (Harvey, Tuttle, & Bell, 1995;Magri et al, 2018) or, on the contrary, favour nutrient immobilisation (e.g. phosphorous and iron) via adsorption or precipitation (e.g.…”