TY - JOUR

T1 - Contribution of Particulate and Mineral-Associated Organic Matter to Potential Denitrification of Agricultural Soils

AU - Surey, Ronny

AU - Kaiser, Klaus

AU - Schimpf, Corinna M.

AU - Mueller, Carsten W.

AU - Boettcher, Jurgen

AU - Mikutta, Robert

PY - 2021

Y1 - 2021

N2 - Water-extractable organic carbon (WEOC) is considered as the most important carbon (C) source for denitrifying organisms, but the contribution of individual organic matter (OM) fractions (i.e., particulate (POM) and mineral-associated (MOM)) to its release and, thus, to denitrification remains unresolved. Here we tested short-time effects of POM and MOM on potential denitrification and estimated the contribution of POM- and MOM-derived WEOC to denitrification and CO2 production of three agricultural topsoils. Suspensions of bulk soils with and without addition of soil-derived POM or MOM were incubated for 24 h under anoxic conditions. Acetylene inhibition was used to determine the potential denitrification and respective product ratio at constant nitrate supply. Normalized to added OC, effects of POM on CO2 production, total denitrification, and its product ratios were much stronger than those of MOM. While the addition of OM generally increased the (N2O + N-2)-N/CO2-C ratio, the N2O/(N2O + N-2) ratio changed differently depending on the soil. Gas emissions and the respective shares of initial WEOC were then used to estimate the contribution of POM and MOM-derived WEOC to total CO2, N2O, and N2O + N-2 production. Water-extractable OC derived from POM accounted for 53-85% of total denitrification and WEOC released from MOM accounted for 15-47%. Total gas emissions from bulk soils were partly over- or underestimated, mainly due to nonproportional responses of denitrification to the addition of individual OM fractions. Our findings show that MOM plays a role in providing organic substrates during denitrification but is generally less dominant than POM. We conclude that the denitrification potential of soils is not predictable based on the C distribution over POM and MOM alone. Instead, the source strength of POM and MOM for WEOC plus the WEOC's quality turned out as the most decisive determinants of potential denitrification.

AB - Water-extractable organic carbon (WEOC) is considered as the most important carbon (C) source for denitrifying organisms, but the contribution of individual organic matter (OM) fractions (i.e., particulate (POM) and mineral-associated (MOM)) to its release and, thus, to denitrification remains unresolved. Here we tested short-time effects of POM and MOM on potential denitrification and estimated the contribution of POM- and MOM-derived WEOC to denitrification and CO2 production of three agricultural topsoils. Suspensions of bulk soils with and without addition of soil-derived POM or MOM were incubated for 24 h under anoxic conditions. Acetylene inhibition was used to determine the potential denitrification and respective product ratio at constant nitrate supply. Normalized to added OC, effects of POM on CO2 production, total denitrification, and its product ratios were much stronger than those of MOM. While the addition of OM generally increased the (N2O + N-2)-N/CO2-C ratio, the N2O/(N2O + N-2) ratio changed differently depending on the soil. Gas emissions and the respective shares of initial WEOC were then used to estimate the contribution of POM and MOM-derived WEOC to total CO2, N2O, and N2O + N-2 production. Water-extractable OC derived from POM accounted for 53-85% of total denitrification and WEOC released from MOM accounted for 15-47%. Total gas emissions from bulk soils were partly over- or underestimated, mainly due to nonproportional responses of denitrification to the addition of individual OM fractions. Our findings show that MOM plays a role in providing organic substrates during denitrification but is generally less dominant than POM. We conclude that the denitrification potential of soils is not predictable based on the C distribution over POM and MOM alone. Instead, the source strength of POM and MOM for WEOC plus the WEOC's quality turned out as the most decisive determinants of potential denitrification.

KW - denitrification potential

KW - nitrous oxide

KW - carbon dioxide

KW - organic matter fractions

KW - water-extractable OM

KW - particulate OM

KW - mineral-associated OM

KW - agricultural soils

KW - NITROUS-OXIDE REDUCTION

KW - DENSITY FRACTIONS

KW - N2O EMISSION

KW - CARBON

KW - DECOMPOSITION

KW - SORPTION

KW - NITRATE

KW - LITTER

KW - BIODEGRADATION

KW - INHIBITION

U2 - 10.3389/fenvs.2021.640534

DO - 10.3389/fenvs.2021.640534

M3 - Journal article

VL - 9

JO - Frontiers in Environmental Science

JF - Frontiers in Environmental Science

SN - 2296-665X

M1 - 640534

ER -