Stable-Isotope-Aided Investigation of the Effect of Redox Potential on Nitrous Oxide Emissions as Affected by Water Status and N Fertilization

Abstract

Soils are the dominant source of atmospheric nitrous oxide (N2O), especially agricultural soils that experience both waterlogging and intensive nitrogen fertilization. However, soil heterogeneity and the irregular occurrence of hydrological events hamper the prediction of the temporal and spatial dynamics of N2O production and transport in soils. Because soil moisture influences soil redox potential, and as soil N cycling processes are redox-sensitive, redox potential measurements could help us to better understand and predict soil N cycling and N2O emissions. Despite its importance, only a few studies have investigated the control of redox potential on N2Oemission from soils in detail. This study aimed to partition the different microbial processes involved in N2O production (nitrification and denitrification) by using redox measurements combined with isotope analysis at natural abundance and 15N-enriched. To this end, we performed long-term laboratory lysimeter experiments to mimic common agricultural irrigation and fertilization procedures. In addition, we used isotope analysis to characterize the distribution and partitioning of N2O sources and explored the 15N-N2O site preference to further constrain N2O microbial processes. We found that irrigation, saturation, and drainage induced changes in soil redox potential, which were closely related to changes in N2O emission from the soil as well as to changes in the vertical concentration profiles of dissolved N2O, nitrate (NO3−) and ammonium (NH4+). The results showed that the redox potential could be used as an indicator for NH4+, NO3−, and N2O production and consumption processes along the soil profile. For example, after a longer saturation period of unfertilized soil, the NO3− concentration was linearly correlated with the average redox values at the different depths (R2 = 0.81). During the transition from saturation to drainage, but before fertilization, the soil showed an increase in N2O emissions, which originated mainly from nitrification as indicated by the isotopic signatures of N2O (δ15N bulk, δ18O and 15N-N2O site preference). After fertilization, N2O still mainly originated from nitrification at the beginning, also indicated by high redox potential and the increase of dissolved NO3−. Denitrification mainly occurred during the last saturation period, deduced from the simultaneous 15N isotope analysis of NO3− and N2O. Our findings suggest that redox potential measurements provide suitable information for improving the prediction of soil N2O emissions and the distribution of mineral N species along the soil profile under different hydrological and fertilization regimes.

Ratoon Rice Cropping Mitigates the Greenhouse Effect by Reducing CH4 Emissions through Reduction of Biomass during the Ratoon Season

“…Our results revealed that there was no significant difference in cumulative N 2 O emissions between RR and DR (Table 2), which may be attributed to the similar annual growth duration (Table 6) and average N 2 O emission flux between the two cropping systems (Figures S1 and S2C,D). In addition, soil moisture has great impacts on nitrification and denitrification associated with N 2 O production [38]. In this study, annual precipitation during rice growth was similar between RR and DR (Table 6).…”

Investigating the controls on greenhouse gas emission in the riparian zone of a small headwater catchment using an automated monitoring system

“…The different oxidizing or reducing conditions govern the dynamics of CO 2 , N 2 O, and CH 4 , and significant CH 4 production (methanogenesis) is generally active when soils are under strictly reducing conditions (Yu et al, 2008). Numerous studies investigated relationships between soil water saturation and soil Eh due to the influence of groundwater (Cogger et al, 1992;Comerford et al, 1996;Seybold et al, 2002;Thomas et al, 2009;Vepraskas & Wilding, 1983;Wanzek et al, 2018), water table changes (McDaniel et al, 2001), flooding (Brettar et al, 2002;Rinklebe et al, 2016), and irrigation (Wang et al, 2020). Redox conditions in wetland soils are strongly influenced by groundwater level fluctuations, leading to relatively fast (hourly) spatial and temporal changes of oxic and anoxic conditions and correspondingly to changes in the predominance of processes of the N cycle (i.e., ammonification and nitrification vs. denitrification) (Clément et al, 2002;Reddy et al, 1989).…”