Postfire nitrogen balance of Mediterranean shrublands: Direct combustion losses versus gaseous and leaching losses from the postfire soil mineral nitrogen flush

Abstract

Fire is a major factor controlling global carbon (C) and nitrogen (N) cycling. While direct C and N losses caused by combustion have been comparably well established, important knowledge gaps remain on postfire N losses. Here, we quantified both direct C and N combustion losses as well as postfire gaseous losses (N O, NO and N ) and N leaching after a high-intensity experimental fire in an old shrubland in central Spain. Combustion losses of C and N were 9.4 Mg C/ha and 129 kg N/ha, respectively, representing 66% and 58% of initial aboveground vegetation and litter stocks. Moreover, fire strongly increased soil mineral N concentrations by several magnitudes to a maximum of 44 kg N/ha 2 months after the fire, with N largely originating from dead soil microbes. Postfire soil emissions increased from 5.4 to 10.1 kg N ha year for N , from 1.1 to 1.9 kg N ha year for NO and from 0.05 to 0.2 kg N ha year for N O. Maximal leaching losses occurred 2 months after peak soil mineral N concentrations, but remained with 0.1 kg N ha year of minor importance for the postfire N mass balance. N stable isotope labelling revealed that 33% of the mineral N produced by fire was incorporated in stable soil N pools, while the remainder was lost. Overall, our work reveals significant postfire N losses dominated by emissions of N that need to be considered when assessing fire effects on ecosystem N cycling and mass balance. We propose indirect N gas emissions factors for the first postfire year, equalling to 7.7% (N -N), 2.7% (NO-N) and 5.0% (N O-N) of the direct fire combustion losses of the respective N gas species.

Effects of two wood-based biochars on the fate of added fertilizer nitrogen—a 15N tracing study

“…Instead, these results suggest that biochar stimulated the loss of 15 NO 3 treatments (Fig. 3g and h) indicates that part of the added 15 NH 4 + -N was converted to 15 NO 3 − -N (through nitrification), which is in line with the findings that biochar can stimulate the nitrification process (Berglund et al 2004;Dannenmann et al 2018 (Mandal et al 2018;Sha et al 2019) (Schomberg et al 2012;Sun et al 2019). Contrary to this, others have outlined the potential of biochar to enhance the adsorbtion of NH 4 + and NH 3 , and hence decrease NH 3 volatilization (Mandal et al 2016;Taghizadeh-Toosi et al 2012;Sun et al 2020).…”

“…However, based on previous studies, it is possible that the reduced N 2 O emissions in biochar treatments might be a result of the limited accessibility of NO 3 − -N retained in the pores of biochar for denitrification (Cayuela et al 2013;Haider et al 2016;Van Zwieten et al 2014). In addition, through the increased soil pH, biochar could have promoted complete denitrification from NO 3 − to N 2 instead of N 2 O as the end product of denitrification (Cayuela et al 2013;Dannenmann et al 2018;Harter et al 2013;Sánchez-García et al 2014). The biochar treatments at both application rates had a pH higher than 7, which favors the synthesis and assembly of N 2 O reductase, promoting N 2 as the final product of denitrification over N 2 O (Bergaust et al 2010).…”

Drought and its legacy modulate the post‐fire recovery of soil functionality and microbial community structure in a Mediterranean shrubland

“…However, some soil functions (soil respiration and enzyme activities) did not recover 6 years after the fire. Consequently, a significant increase in soil nitrate, ammonium, and phosphate has been reported to occur immediately after fire, mainly as an effect of pyromineralization (Dannenmann et al, ; Hinojosa et al, ; Karhu et al, ). However, results obtained here suggest that such changes were transient since they disappeared in the second spring after fire.…”

“…Rainfall occurs from autumn to spring (93%), while summer is dry (Los Cortijos meteorological station, 39°19′N, 4°04′W; Agencia Estatal de Meteorología, Spain). The top 5 cm of soil is sandy loam (68%, 18%, and 14% sand, silt, and clay, respectively) forming a Dystric Cambisol (FAO and IUSS Working Group WRB, ), with a high proportion of pebbles (40%), the parent rock being mainly quartzite, 6.5 pH, and a 11.5 C:N ratio (see Dannenmann et al, , for further details about the whole soil profile of the study area).…”

Scaling Contagious Disturbance: A Spatially-Implicit Dynamic Model

“…Contagious disturbances mediate biogeochemical fluxes, are drivers of landscape ecology, and contribute uncertainty to understanding consequences of anthropogenic climate change. At the end of the twentieth century on average, 608 Mha of land burned per year globally, affecting nutrient cycles, community composition, and altering local energy budgets (Mouillot and Field, 2005;Marlon et al, 2012;Parks et al, 2016;Dannenmann et al, 2018). Anthropogenic land-use-change also often follows a contagious pattern, beyond its total area and carbon impact, it is a major driver of habitat fragmentation, with 75% of forests globally located <1 km from an edge (Haddad et al, 2015).…”