Germinating wheat promotes the emission of atmospherically significant nitrous acid (HONO) gas from soils

Denitrification is the major nitrous acid production pathway in boreal agricultural soils

“…The current global HONO budget is not balanced when all known sources and sinks are included, which suggests that there is a missing source of HONO [6][7][8] . Although soils have only recently been identified as important HONO emitters [9][10][11][12][13][14][15][16][17] , soils have been proposed as a key component of this missing HONO source. Soil nitrite (NO 2 − ) may be the key HONO precursor 9 but this has not yet been directly demonstrated using 15 N tracer approaches and accounting for primary microbial pathways producing it.…”

“…Although soils have only recently been identified as important HONO emitters [9][10][11][12][13][14][15][16][17] , soils have been proposed as a key component of this missing HONO source. Soil nitrite (NO 2 − ) may be the key HONO precursor 9 but this has not yet been directly demonstrated using 15 N tracer approaches and accounting for primary microbial pathways producing it. Nitrite is mainly produced during microbial ammonia (NH 3 ) oxidation (autotrophic and heterotrophic nitrification) and nitrate (NO 3 − ) reduction (denitrification and dissimilatory nitrate reduction to ammonium (DNRA)) pathways [18][19][20] .…”

“…In addition, direct release of HONO by NH 3 oxidizers (autotrophic nitrifiers) has also been demonstrated 10,21 . Although the mechanisms that underpin HONO production are not yet fully understood, several studies have demonstrated the importance of microbial pathways in soil HONO production [9][10][11][12][13][14][15][16][17] . However, abiotic pathways (e.g., hydro-xylamine+water = HONO) have been proposed but have not been investigated in soils to date 21 .…”

“…The first evidence on a potential link between soil HONO emissions and underlying microbial processes was provided conducting 15 N tracer experiments, showing that nitrifiers outpaced denitrifiers in soil HONO emissions 22 . Another study 23 , proving the concept, also provided evidence on the participation of microbial processes in soil HONO emissions, especially the involvement of NH 3 oxidizers (nitrifiers) by using 15 N-labeled urea.…”

“…The first evidence on a potential link between soil HONO emissions and underlying microbial processes was provided conducting 15 N tracer experiments, showing that nitrifiers outpaced denitrifiers in soil HONO emissions 22 . Another study 23 , proving the concept, also provided evidence on the participation of microbial processes in soil HONO emissions, especially the involvement of NH 3 oxidizers (nitrifiers) by using 15 N-labeled urea. To date, only one systematic study has addressed the pathways of soil HONO formation using a tracer approach (labeled ammonium ( 15 NH 4 + )), highlighting the sole importance of NH 3 oxidizers in HONO production and excluding the role of NO 3 − reduction in aerobic soils 11 .…”