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Interactions between benthic copepods, bacteria and diatoms promote nitrogen retention in intertidal marine sediments.

Stock W, Heylen K, Sabbe K, Willems A, De Troch M - PLoS ONE (2014)

Bottom Line: Ammonium concentrations were highest in the treatments with copepods or their spent medium, whilst denitrification potential was lowest in these treatments, suggesting that copepods enhance dissimilatory nitrate reduction to ammonium over denitrification.We hypothesize that this is an indirect effect, by providing extra carbon for the bacterial community through the copepods' excretion products, thus changing the C/N ratio in favour of dissimilatory nitrate reduction.Diatoms alone had no effect on the nitrogen fluxes, but they did enhance the effect of copepods, possibly by influencing the quantity and quality of the copepods' excretion products.

View Article: PubMed Central - PubMed

Affiliation: Department of Biology, Ghent University, Ghent, Belgium.

ABSTRACT
The present study aims at evaluating the impact of diatoms and copepods on microbial processes mediating nitrate removal in fine-grained intertidal sediments. More specifically, we studied the interactions between copepods, diatoms and bacteria in relation to their effects on nitrate reduction and denitrification. Microcosms containing defaunated marine sediments were subjected to different treatments: an excess of nitrate, copepods, diatoms (Navicula sp.), a combination of copepods and diatoms, and spent medium from copepods. The microcosms were incubated for seven and a half days, after which nutrient concentrations and denitrification potential were measured. Ammonium concentrations were highest in the treatments with copepods or their spent medium, whilst denitrification potential was lowest in these treatments, suggesting that copepods enhance dissimilatory nitrate reduction to ammonium over denitrification. We hypothesize that this is an indirect effect, by providing extra carbon for the bacterial community through the copepods' excretion products, thus changing the C/N ratio in favour of dissimilatory nitrate reduction. Diatoms alone had no effect on the nitrogen fluxes, but they did enhance the effect of copepods, possibly by influencing the quantity and quality of the copepods' excretion products. Our results show that small-scale biological interactions between bacteria, copepods and diatoms can have an important impact on denitrification and hence sediment nitrogen fluxes.

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NO3- reduction and N2O production rates.NO3- reduction rate (black bars; left y-axis) and N2O production rates (white bars; right y-axis) during the measurement of the denitrification potential for the different treatments (mean ± SE; cop.  =  copepods; cop. + dia.  =  copepod+ diatom). The different letters above the bar indicate significant differences (P<0.05; DTK) between the treatments. Light conditions (not shown) did not affect the outcome of treatments.
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pone-0111001-g001: NO3- reduction and N2O production rates.NO3- reduction rate (black bars; left y-axis) and N2O production rates (white bars; right y-axis) during the measurement of the denitrification potential for the different treatments (mean ± SE; cop.  =  copepods; cop. + dia.  =  copepod+ diatom). The different letters above the bar indicate significant differences (P<0.05; DTK) between the treatments. Light conditions (not shown) did not affect the outcome of treatments.

Mentions: The NO3- reduction and N2O production rates did not differ between light conditions. In contrast to the NO3- reduction rate, which did not differ between treatments (Fig 1, black bars), the N2O production rate did significantly differ between the treatments (p<0.01; Fig. 1, white bars). The N2O production rate was significantly lower for the copepod + diatom treatment compared to the blank (p<0.001), diatom (p<0.001), increased NO3- (p<0.001) and spent medium (p<0.001) treatments.


Interactions between benthic copepods, bacteria and diatoms promote nitrogen retention in intertidal marine sediments.

Stock W, Heylen K, Sabbe K, Willems A, De Troch M - PLoS ONE (2014)

NO3- reduction and N2O production rates.NO3- reduction rate (black bars; left y-axis) and N2O production rates (white bars; right y-axis) during the measurement of the denitrification potential for the different treatments (mean ± SE; cop.  =  copepods; cop. + dia.  =  copepod+ diatom). The different letters above the bar indicate significant differences (P<0.05; DTK) between the treatments. Light conditions (not shown) did not affect the outcome of treatments.
© Copyright Policy
Related In: Results  -  Collection

License
Show All Figures
getmorefigures.php?uid=PMC4215923&req=5

pone-0111001-g001: NO3- reduction and N2O production rates.NO3- reduction rate (black bars; left y-axis) and N2O production rates (white bars; right y-axis) during the measurement of the denitrification potential for the different treatments (mean ± SE; cop.  =  copepods; cop. + dia.  =  copepod+ diatom). The different letters above the bar indicate significant differences (P<0.05; DTK) between the treatments. Light conditions (not shown) did not affect the outcome of treatments.
Mentions: The NO3- reduction and N2O production rates did not differ between light conditions. In contrast to the NO3- reduction rate, which did not differ between treatments (Fig 1, black bars), the N2O production rate did significantly differ between the treatments (p<0.01; Fig. 1, white bars). The N2O production rate was significantly lower for the copepod + diatom treatment compared to the blank (p<0.001), diatom (p<0.001), increased NO3- (p<0.001) and spent medium (p<0.001) treatments.

Bottom Line: Ammonium concentrations were highest in the treatments with copepods or their spent medium, whilst denitrification potential was lowest in these treatments, suggesting that copepods enhance dissimilatory nitrate reduction to ammonium over denitrification.We hypothesize that this is an indirect effect, by providing extra carbon for the bacterial community through the copepods' excretion products, thus changing the C/N ratio in favour of dissimilatory nitrate reduction.Diatoms alone had no effect on the nitrogen fluxes, but they did enhance the effect of copepods, possibly by influencing the quantity and quality of the copepods' excretion products.

View Article: PubMed Central - PubMed

Affiliation: Department of Biology, Ghent University, Ghent, Belgium.

ABSTRACT
The present study aims at evaluating the impact of diatoms and copepods on microbial processes mediating nitrate removal in fine-grained intertidal sediments. More specifically, we studied the interactions between copepods, diatoms and bacteria in relation to their effects on nitrate reduction and denitrification. Microcosms containing defaunated marine sediments were subjected to different treatments: an excess of nitrate, copepods, diatoms (Navicula sp.), a combination of copepods and diatoms, and spent medium from copepods. The microcosms were incubated for seven and a half days, after which nutrient concentrations and denitrification potential were measured. Ammonium concentrations were highest in the treatments with copepods or their spent medium, whilst denitrification potential was lowest in these treatments, suggesting that copepods enhance dissimilatory nitrate reduction to ammonium over denitrification. We hypothesize that this is an indirect effect, by providing extra carbon for the bacterial community through the copepods' excretion products, thus changing the C/N ratio in favour of dissimilatory nitrate reduction. Diatoms alone had no effect on the nitrogen fluxes, but they did enhance the effect of copepods, possibly by influencing the quantity and quality of the copepods' excretion products. Our results show that small-scale biological interactions between bacteria, copepods and diatoms can have an important impact on denitrification and hence sediment nitrogen fluxes.

Show MeSH