Nitrous oxide production and isotopomer composition by fungi isolated from salt marsh sediments

Abstract

The emissions of nitrous oxide (N2O), a potent greenhouse gas and ozone-depleting agent, have been steadily increasing from coastal environments, such as salt marsh sediments, as a result of anthropogenic nutrient loading. Biotic processes, including nitrification and denitrification, are the largest sources of N2O from salt marsh sediments. While it is assumed that the bulk of N2O from salt marsh sediment is produced by nitrification and bacterial denitrification, recent reports suggest fungal denitrification may contribute significantly. In this study, four fungi capable of growth under sulfidic conditions were isolated from salt marsh sediments in North Inlet, South Carolina, USA. Fungal species included Purpureocillium lilacinum, Trichoderma harzianum, Trichoderma virens, and Rhodotorula glutinis, as determined by sequencing the18S and 28S rRNA genes. The isotopomer signatures of N2O produced by these fungi were measured using isotope ratio mass spectrometry, which can be used to estimate the contribution of different sources of N2O. Up to 22.8% of nitrite provided in growth media was converted to N2O by fungal strains isolated from salt marsh sediments. The site preference (SP) of N2O produced by salt marsh sediment fungi ranged from 7.5 ± 1.6‰ to 33.4 ± 1.2‰. These values are lower than the SP of N2O from the model fungal denitrifier Fusarium oxysporum (37.1 ± 2.5‰), which is the SP typically used as an endmember in isotope mass balance considerations. The N2O SP values we measured expand the range of N2O SP used for isotope mass balances calculations to determine the relative contribution of fungi to N2O production in salt marsh sediments.

Planktonic Marine Fungi: A Review

“…Specifically, many fungal species can perform incomplete denitrification, the dissimilatory reduction of nitrate sequentially to nitrite, nitric oxide, and nitrous oxide (Maeda et al., 2015). While fungal denitrification is an important process in soil (H. Chen et al., 2014; Laughlin & Stevens, 2002), this process has been reported in marine environments (Lazo‐Murphy et al., 2022; Su et al., 2021; Wankel et al., 2017), including the eastern tropical North Pacific oxygen minimum zone (Peng & Valentine, 2021). On one hand this suggests fungi make a small (up to 10%) but significant contribution to fixed nitrogen loss from the ocean water columns.…”

Isotopomer labeling and oxygen dependence of hybrid nitrous oxide production

“…Here, the high rates of N2O production from NO3measured within the ODZ core support this hypothesis. While most denitrifying strains produce N2O with δ( 15 N sp ) ≈ 0‰ (Sutka et al 2006), at least one strain of denitrifying bacteria can produce N2O with δ( 15 N sp ) = 22‰ (Toyoda et al 2005) and denitrifying fungi produce N2O with δ( 15 N sp ) = 35-37‰ (Sutka et al 2008;Rohe et al 2014;Yang et al 2014;Lazo-Murphy et al 2022). High rates of N2O production from 15 N-NO3 -, combined with natural abundance isotopomer studies, suggest that strains of denitrifying bacteria and fungi with characteristics similar to these cultured examples may be important contributors to N2O in the core of ODZs.…”

Planktonic marine fungi: A review

“…Specifically, many fungal species can perform incomplete denitrification, the dissimilatory reduction of nitrate sequentially to nitrite, nitric oxide, and nitrous oxide (Maeda et al, 2015). While fungal denitrification is an important process in soil Laughlin & Stevens, 2002), this process has been reported in marine environments (Lazo-Murphy et al, 2022;Su et al, 2021;Wankel et al, 2017), including the eastern tropical North Pacific oxygen minimum zone (Peng & Valentine, 2021). On one hand this suggests fungi make a small (up to 10%) but significant contribution to fixed nitrogen loss from the ocean water columns.…”