Nutrient Enrichment Alters Salt Marsh Fungal Communities and Promotes Putative Fungal Denitrifiers

Abstract

Enrichment of ecosystems with excess nutrients is occurring at an alarming rate and has fundamentally altered ecosystems worldwide. Salt marshes, which lie at the land-sea interface, are highly effective at removing anthropogenic nutrients through the action of macrophytes and through microbial processes in coastal sediments. The response of salt marsh bacteria to excess nitrogen has been documented; however, the role of fungi and their response to excess nitrogen in salt marsh sediments is not fully understood. Here, we document the response of salt marsh fungal communities to long-term excess nitrate in four distinct marsh habitats within a northern temperate marsh complex. We show that salt marsh fungal communities varied as a function of salt marsh habitat, with both fungal abundance and diversity increasing with carbon quantity. Nutrient enrichment altered fungal communities in all habitats through an increase in fungal abundance and the proliferation of putative fungal denitrifiers. Nutrient enrichment also altered marsh carbon quality in low marsh surface sediments where fungal response to nutrient enrichment was most dramatic, suggesting nutrient enrichment can alter organic matter quality in coastal sediments. Our results indicate that fungi, in addition to bacteria, likely play an important role in anaerobic decomposition of salt marsh sediment organic matter.

Metagenomics coupled with biogeochemical rates measurements provide evidence that nitrate addition stimulates respiration in salt marsh sediments

“…Greater availability of NO 3 − could potentially diminish the carbon storage capacity of salt marsh sediments as NO 3 − is an energetically favorable electron acceptor compared to sulfate (SO 4 2− ), and hence stimulates subsurface microbial respiration where OM is oxidized to fuel heterotrophic processes (Bulseco et al ). A number of studies have documented how microbes respond to increased NO 3 − supply, either through shifts in the active bacterial community (Kearns et al ), increased diversity and abundance of putative fungal denitrifiers (Kearns et al ), or increased functional potential for denitrification (Graves et al ). Several studies have also observed changes to ecosystem function in response to NO 3 − , including increased rates of denitrification and dissimilatory NO 3 − reduction to ammonium (DNRA; Koop‐Jakobsen and Giblin ).…”

Competitive exclusion and metabolic dependency among microorganisms structure the cellulose economy of agricultural soil

“…Both Cellvibrio and Chaetomium are commonly more abundant in tilled versus untilled fields ( Figure S9) [77][78][79][80] and, the latter in disturbed forest soils [81]. The occurrence of Chaetomium in agroecosystems may be linked to nitrogen fertilization, given their enrichment in Nfertilized fields and wetlands [82][83][84]. The predominance of these ruderal cellulolytic taxa is indicative of the frequent soil disturbances in agroecosystems.…”

Drivers and modelling of blue carbon stock variability in sediments of southeastern Australia

“…However, reduced nutrient inputs to coastal ecosystems could benefit C sequestration, as nutrient additions can result in net C loss through plant mortality, erosion, efflux, and remineralization via enhanced microbial activity (Macreadie et al, 2017b). Further, excess N has been linked to enhanced decomposition and an overall increase in tidal marsh ecosystem respiration due to shifts in microbial communities (Kearns et al, 2018).…”