Biochar as electron donor for reduction of N2O by Paracoccus denitrificans

Abstract

Biochar (BC) has been shown to influence microbial denitrification and mitigate soil N2O emissions. However, it is unclear if BC is able to directly stimulate the microbial reduction of N2O to N2. We hypothesized that the ability of BC to lower N2O emissions could be related not only to its ability to store electrons, but to donate them to bacteria that enzymatically reduce N2O. Therefore, we carried out anoxic incubations with Paracoccus denitrificans, known amounts of N2O, and nine contrasting BCs, in the absence of any other electron donor or acceptor. We found a strong and direct correlation between the extent and rates of N2O reduction with BC's EDC/EEC (electron donating capacity/electron exchange capacity). Apart from the redox capacity, other BC properties were found to regulate the BC's ability to increase N2O reduction by P. denitrificans. For this specific BC series, we found that a high H/C and ash content, low surface area and poor lignin feedstocks favored N2O reduction. This provides valuable information for producing tailored BCs with the potential to assist and promote the reduction of N2O in the pursuit of reducing this greenhouse gas emissions.

Increased N2 emissions from an arable soil four years after biochar application#

“…In contrast to our findings, Chintala et al (2015) who carried out a one week-incubation using mixtures of soil and fresh BCs reported that the increase in total denitrification was distinctly higher in the control than in BC-treated samples. The differences between the findings of our study and the one by Chintala et al (2015) might be explained by a stronger electron shuttle function of BC in our study highlighting the importance of the properties of the BCs used (Bakshi et al, 2016;Pascual et al, 2020;Yuan et al, 2019).…”

“…The differences between the findings of our study and the one by Chintala et al. (2015) might be explained by a stronger electron shuttle function of BC in our study highlighting the importance of the properties of the BCs used (Bakshi et al., 2016; Pascual et al., 2020; Yuan et al., 2019).…”

“…In more recent publications, the electron shuttle function of BC proposed by Cayuela et al. (2013) was confirmed, that is, BC can act as an electron shuttle stimulating microbial reduction of N 2 O to N 2 (Pascual et al., 2020; Yuan et al., 2019). It is, however, not clear, whether this function is maintained if BC ages (Yuan et al., 2019), since the physical and chemical properties of BC significantly change during aging (Bakshi et al., 2016).…”

“…The general lack of detectable N 2 O emissions may be explained by soil conditions favorable for the reduction of N 2 O to N 2 , that is, a high pH (7.5), sufficient C available for complete denitrification as suggested by EOC/NO 3 ratios (Table 2) markedly above the minimum supply C/N ratios for heterotrophic microorganisms (≈ 3), and the positive relation between N 2 fluxes and NO 3 –N concentrations (Lan et al., 2017; Zhang et al., 2020). The significantly higher N 2 emissions in the BC‐treated soil may be explained by the electron shuttle function of BC, that is, its ability to store and donate electrons to denitrifying microorganisms (Pascual et al., 2020; Yuan et al., 2019). In 2011, the C org content amounted to 6.6% (BC) and 1.7% (control), respectively (Karer et al., 2013).…”

How biochar works, and when it doesn't: A review of mechanisms controlling soil and plant responses to biochar

“…Biochar can lower denitrification (the reduction of to N 2 ) by: (i) facilitating the last step of denitrification (the transformation of N 2 O to N 2 ), and (ii) decreasing total denitrification activity (Cayuela et al, 2013; Weldon et al, 2019). Biochar can facilitate the reduction of N 2 O to N 2 via: (i) increasing pH in acid soils (Obia et al, 2015) thus enhancing the nosZ gene (Harter, Guzman‐Bustamante, et al, 2016); (ii) changing the relative abundance and composition of N 2 O‐reducing microbial communities (Harter, Weigold, et al, 2016); and (iii) facilitating extracellular electron exchange (Chen et al, 2014) or directly donating electrons to denitrifying bacteria (Pascual, Sánchez‐Monedero, Cayuela, et al, 2020). The decrease in denitrification may result from decrease in availability of NO 3 − and bioavailable C substrate (Fiorentino et al, 2019; Hagemann, Kammann, et al, 2017; Heaney et al, 2020).…”