Dominance of bacterial ammonium oxidizers and fungal denitrifiers in the complex nitrogen cycle pathways related to nitrous oxide emission

Abstract

Organic compounds and mineral nitrogen (N) usually increase nitrous oxide (N 2 O) emissions. Vinasse, a by-product of bio-ethanol production that is rich in carbon, nitrogen, and potassium, is recycled in sugarcane fields as a bio-fertilizer. Vinasse can contribute significantly to N 2 O emissions when applied with N in sugarcane plantations, a common practice. However, the biological processes involved in N 2 O emissions under this management practice are unknown. This study investigated the roles of nitrification and denitrification in N 2 O emissions from straw-covered soils amended with different vinasses (CV: concentrated and V: nonconcentrated) before or at the same time as mineral fertilizers at different time points of the sugarcane cycle in two seasons. N 2 O emissions were evaluated for 90 days, the period that occurs most of the N 2 O emission from fertilizers; the microbial genes encoding enzymes involved in N 2 O production (archaeal and bacterial amoA, fungal and bacterial nirK, and bacterial nirS and nosZ), total bacteria, and total fungi were quantified by real-time PCR. The application of CV and V in conjunction with mineral N resulted in higher N 2 O emissions than the application of N fertilizer alone. The strategy of vinasse application 30 days before mineral N reduced N 2 O emissions by 65% for CV, but not for V. Independent of rainy or dry season, the microbial processes were nitrification by ammonia-oxidizing bacteria (AOB) and archaea and denitrification by bacteria and fungi. The contributions of each process differed and depended on soil moisture, soil pH, and N sources. We concluded that amoA-AOB was the most important gene related to N 2 O emissions, which indicates that nitrification by AOB is the main microbial-driven process linked to N 2 O emissions in tropical soil. Interestingly, fungal nirK was also significantly correlated with N 2 O emissions, suggesting that denitrification by fungi contributes to N 2 O emission in soils receiving straw and vinasse application. K E Y W O R D Sdenitrification, dry-wet season, greenhouse gas, microbial ecology, nitrification, quantitative real-time

Implications of Sugarcane Straw Removal for Soil Greenhouse Gas Emissions in São Paulo State, Brazil

“…N content in the straw, 4.9 g kg −1 [6]. Tier 1 -IPCC approach; Tier 2 -Regional-specific approach based on data from this study Implications of Straw Removal for Soil N 2 O Emissions Despite being highly variable, the daily N 2 O emissions (ranging from 0.2 to 4.1 kg N 2 O-N ha −1 year −1 ) observed in this study are of the same magnitude as those reported in other studies conducted in sugarcane in Brazil [11,12,17,18,31]. The N 2 O emissions induced by N fertilizer plus straw removal in sugarcane fields were clearly site-specific (Fig.…”

“…But once N is applied to the soil, several processes occur before N absorption by sugarcane plants, including volatilization, lixiviation, and/or N 2 O emission [16]. The latter is formed in the soil mostly by the microbial processes of nitrification and denitrification [17,18], which are highly influenced by moisture, temperature, and soil physical and chemical conditions. Methane (CH 4 ) is another important GHG (GWP of 28 times higher than CO 2 ) in agricultural environments [10], but so far little or no effect of straw maintenance on CH 4 emissions has been observed in Brazilian sugarcane fields [11,19], despite the higher soil moisture and organic C input caused by the straw mulching.…”

Elevated temperature shifts soil N cycling from microbial immobilization to enhanced mineralization, nitrification and denitrification across global terrestrial ecosystems

“…Concerning the increased nirS gene abundance, with no change in nirK gene abundance for soils with plants (Figure 4), we postulate that nirS genes are more sensitive to warming and probably contribute more to N 2 O production than nirK genes. However, fungal nirK genes that were not included in this meta‐analysis, might also play an important role in N 2 O production in terrestrial ecosystems (Laughlin & Stevens, 2002; Lourenço et al., 2018). This premise is based on the purported higher tolerance of fungal nirK genes to elevated temperatures (up to 40°C) compared to bacterial nirK genes (Xu et al, 2017b).…”

Nitrification inhibitors effectively target N2O‐producing Nitrosospira spp. in tropical soil

“…Further, the nitrite oxidizer bacteria Nitrobacter and Nitrospira have optimal growth under higher and lower nitrite supplies, respectively, which is linked to their ecological niches (Attard et al, 2010;Nowka et al, 2015). Nitrification is doubly implicated in N 2 O production, either directly or indirectly by producing NO 3 − as the basis for denitrification, and has been shown to be the main process involved in N 2 O emissions in some Brazilian sugarcane soils (Liu et al, 2016;Soares et al, 2016;Wu et al, 2017aWu et al, , 2017bLourenço et al, 2018aLourenço et al, , 2018b. The addition of nitrification inhibitors with nitrogen fertilizers is currently being explored as a sustainable management practice in Brazilian sugarcane Soares et al, 2015Soares et al, , 2016.…”