Management of soil pH promotes nitrous oxide reduction and thus mitigates soil emissions of this greenhouse gas

While concerns about human-induced effects on the Earth’s climate have mainly concentrated on carbon dioxide (CO2) and methane (CH4), reducing anthropogenic nitrous oxide (N2O) flux, mainly of agricultural origin, also represents an opportunity for substantial mitigation. To develop a solution that induces neither the transfer of nitrogen pollution nor decreases agricultural production, we specifically investigated the last step of the denitrification pathway, the N2O reduction path, in soils. We first observed that this path is mainly driven by soil pH and is progressively inhibited when pH is lower than 6.8. During field experiments, we observed that liming acidic soils to neutrality made N2O reduction more efficient and decreased soil N2O emissions. As we estimated acidic fertilized soils to represent 37% [27–50%] of French soils, we calculated that liming could potentially decrease France’s total N2O emissions by 15.7% [8.3–21.2%]. Nevertheless, due to the different possible other impacts of liming, we currently recommend that the deployment of this solution to mitigate N2O emission should be based on local studies that take into account agronomic, environmental and economic aspects.

Biochar Enhances Nitrous Oxide Reduction in Acidic but Not in Near-Neutral pH Soil

We quantified nitrous oxide (N2O) fluxes and total denitrification (N2O + N2) in an acidic (Ferralsol) and a near-neutral pH soil (Cambisol) to determine whether biochar’s alkalinization effect could be the mechanism inducing potential reductions in N2O fluxes. In Ferralsol, decreases in N2O emissions and in the N2O to N2O + N2 ratio were observed in both biochar and lime treatments. In Cambisol, neither biochar nor lime decreased N2O emissions, despite significantly increasing soil pH. The abundance and community structure of nosZ gene-bearing microorganisms indicated that gene abundances did not explain biochar effects, but a higher diversity of nosZ gene-bearing microorganisms correlated to lower total denitrification. Overall, our results suggest that biochar’s potential to decrease N2O emissions, through soil alkalinization, may be more effective in acidic soils.

FISIOLOGI PERTUMBUHAN, POTENSI AKTIFITAS PRODUKSI N2O DAN GEN FUNGSIONAL PENYANDINYA PADA BEBERAPA ISOLAT BAKTERI DENITRIFIKASI

Physiological characters of four denitrifying bacteria (Bacillus sp. CPNS, Bacillus thuringiensis UPT1, Brevundimonas diminuta EA1 and Bacillus sp. UPSB) were studied based on the growth ability on various nitrate concentrations and the production of N2O gas. The characters of denitrifying bacteria were also evaluated through the existence of functional genes nirS and nosZ, encoding the nitrite reduction and nitrous oxide reduction enzymes which have important role on denitrification processes. The study showed that Bacillus sp. UPSB and Bacillus sp. CPNS isolates have a linear growth with the increasing concentration of KNO3. The N2O gas production of Bacillus sp. UPSB isolate was relatively high, about 70 ?/l, Bacillus sp. CPNS isolate was 25?/l, while the Bacillus thuringiensis UPT1 isolate was 5 ?/l and Brevundimonas diminuta EA1 isolate was 8 ?/l. It was also indicated that both Bacillus sp. UPSB and Bacillus sp. CPNS had high deninitrification activities. It was confirmed that all isolates were contained functional gen of nirS and nosZ.