Stimulation of microbial nitrogen cycling in aquatic ecosystems by benthic macrofauna: mechanisms and environmental implications

[摘要] Invertebrate animals that live at the bottom of aquatic ecosystems (i.e.,benthic macrofauna) are important mediators between nutrients in the watercolumn and microbes in the benthos. The presence of benthic macrofaunastimulates microbial nutrient dynamics through different types ofanimal–microbe interactions, which potentially affect the trophic status ofaquatic ecosystems. This review contrasts three types of animal–microbeinteractions in the benthos of aquatic ecosystems: (i) ecosystemengineering, (ii) grazing, and (iii) symbiosis. Their specific contributionsto the turnover of fixed nitrogen (mainly nitrate and ammonium) and theemission of the greenhouse gas nitrous oxide are evaluated.Published data indicate that ecosystem engineering by sediment-burrowingmacrofauna stimulates benthic nitrification and denitrification, whichtogether allows fixed nitrogen removal. However, the release of ammoniumfrom sediments is enhanced more strongly than the sedimentary uptake of nitrate.Ecosystem engineering by reef-building macrofauna increases nitrogenretention and ammonium concentrations in shallow aquatic ecosystems, butallows organic nitrogen removal through harvesting. Grazing by macrofauna onbenthic microbes apparently has small or neutral effects on nitrogencycling. Animal–microbe symbioses provide abundant and distinct benthiccompartments for a multitude of nitrogen-cycle pathways. Recent studiesreveal that ecosystem engineering, grazing, and symbioses of benthicmacrofauna significantly enhance nitrous oxide emission from shallow aquaticecosystems.The beneficial effect of benthic macrofauna on fixed nitrogen removalthrough coupled nitrification–denitrification can thus be offset by theconcurrent release of (i) ammonium that stimulates aquatic primaryproduction and (ii) nitrous oxide that contributes to global warming.Overall, benthic macrofauna intensifies the coupling between benthos,pelagial, and atmosphere through enhanced turnover and transport ofnitrogen.

[学科分类] 地球化学与岩石