Open AccessNitrate transformation and immobilization in particulate organic matter incubations: Influence of redox, iron and (a)biotic conditions
Author(s) -
Fiona R. Kizewski,
Jason P. Kaye,
Carmen Enid Martı́nez
Publication year - 2019
Publication title -
plos one
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.99
H-Index - 332
ISSN - 1932-6203
DOI - 10.1371/journal.pone.0218752
Subject(s) - anoxic waters , abiotic component , environmental chemistry , denitrification , nitrate , organic matter , chemistry , mineralization (soil science) , redox , dissolved organic carbon , nitrogen , ecology , inorganic chemistry , organic chemistry , biology
Nitrate can be reduced to other N inorganic species via denitrification and incorporated into organic matter by immobilization; however, the effect of biotic/abiotic and redox condition on immobilization and denitrification processes from a single system are not well documented. We hypothesize nitrate (NO 3 - ) transformation pathways leading to the formation of dissolved- and solid-phase organic N are predominantly controlled by abiotic reactions, but the formation of soluble inorganic N species is controlled by redox condition. In this study, organic matter in the form of leaf compost (LC) was spiked with 15 NO 3 - and incubated under oxic/anoxic and biotic/abiotic conditions at pH 6.5. We seek to understand how variations in environmental conditions impact NO 3 - transformation pathways through laboratory incubations. We find production of NH 4 + is predominantly controlled by redox whereas NO 3 - conversion to dissolved organic nitrogen (DON) and immobilization in solid-phase N are predominantly controlled by abiotic processes. Twenty % of added 15 N-NO 3 - was incorporated into DON under oxic conditions, with abiotic processes accounting for 85% of the overall incorporation. Nitrogen immobilization processes resulted in N concentrations of 4.1–6.6 μg N (g leaf compost) -1 , with abiotic processes accounting for 100% and 66% of the overall (biotic+abiotic) N immobilization under anoxic and oxic conditions, respectively. 15 N-NMR spectroscopy suggests 15 NO 3 - was immobilized into amide/aminoquinones and nitro/oxime under anoxic conditions. A fraction of the NH 4 + was produced abiotically under anoxic conditions (~10% of the total NH 4 + production) although biotic organic N mineralization contributed to most of NH 4 + production. Our results also indicate Fe(II) did not act as an electron source in biotic-oxic incubations; however, Fe(II) provided electrons for NO 3 - reduction in biotic-anoxic incubations although it was not the sole electron source. It is clear that, under the experimental conditions of this investigation, abiotic and redox processes play important roles in NO 3 - transformations. As climatic conditions change (e.g., frequency/intensity of rainfall), abiotic reactions that shift transformation pathways and N species concentrations from those controlled by biota might become more prevalent.