Elevated atmospheric CO₂ reduces yield‐scaled N₂O fluxes from subtropical rice systems: Six site‐years field experiments

Abstract

Increasing levels of atmospheric CO2 are expected to enhance crop yields and alter soil greenhouse gas fluxes from rice paddies. While elevated CO2 (ECO2) effects on CH4 emissions from rice paddies have been studied in some detail, little is known how ECO2 might affect N2O fluxes or yield‐scaled emissions. Here, we report on a multi‐site, multi‐year in‐situ FACE (free‐air CO2 enrichment) study, aiming to determine N2O fluxes and crop yields from Chinese subtropical rice systems as affected by ECO2. In this study, we tested various N fertilization and residue addition treatments, with rice being grown under either ECO2 (+200 μmol/mol) or ambient control. Across the six site‐years, rice straw and grain yields under ECO2 were increased by 9%–40% for treatments fertilized with ≥150 kg N/ha, while seasonal N2O emissions were decreased by 23%–73%. Consequently, yield‐scaled N2O emissions were significantly lower under ECO2. For treatments receiving insufficient fertilization (≤125 kg N/ha), however, no significant ECO2 effects on N2O emissions were observed. The mitigating effect of ECO2 upon N2O emissions is closely associated with plant N uptake and a reduction of soil N availability. Nevertheless, increases in yield‐scaled N2O emissions with increasing N surplus suggests that N surplus is a useful indicator for assessing N2O emissions from rice paddies. Our findings indicate that with rising atmospheric CO2 soil N2O emissions from rice paddies will decrease, given that the farmers’ N fertilization is usually sufficient for crop growth. The expected decrease in N2O emissions was calculated to compensate 24% of the simultaneously observed increase in CH4 emissions under ECO2. This shows that for an agronomic and environmental assessment of ECO2 effects on rice systems, not only CH4 emissions, but also N2O fluxes and yield‐scaled emissions need to be considered for identifying most climate‐friendly and economically viable options for future rice production.

AMF Inoculation Can Enhance Yield of Transgenic Bt Maize and Its Control Efficiency Against Mythimna separata Especially Under Elevated CO2

“…As a result, Bt crops have been used to control a wider range of pests, such as Helicoverpa armigera (Hübner), Heliothis virescens , and Mythimna separata (Riddick et al, 1998 ; Chen F. J. et al, 2011 ; Chang et al, 2013 ). Meanwhile, human activities, specifically fossil fuel burning and land-use change, are rapidly increasing the level of carbon dioxide (CO 2 ) in the atmosphere (Yu and Chen, 2019 ; Yao et al, 2020 ). Specifically, it has been reported that the atmospheric CO 2 concentration increased from 288 to 405 ppm from 1800 to 2018 ( www.esrl.noaa.gov/gmd/ccgg/trends/ ).…”

Impacts of Elevated Atmospheric CO2 and N Fertilization on N2O Emissions and Dynamics of Associated Soil Labile C Components and Mineral N in a Maize Field in the North China Plain

“…Although Liu et al [5] considered that improving N availability mainly accounted for the enhanced N 2 O emission, the corresponding effect between N-limited natural ecosystems and N-rich agroecosystems was not distinguished. A recent report from a paddy rice field found that after 6 years of continuous observation eCO 2 , N 2 O emissions decreased obviously at an N application rate ≥ 150 kg N ha −1 , but remained unaffected at an N application rate ≤ 125 kg N ha −1 [16]. It should be noted that the paddy rice fields are periodically flooded, which does not occur in cropped upland; thus, it is uncertain whether the conclusions drawn from paddy rice fields are applicable to upland farming.…”

“…N 2 O emissions from croplands with N fertilization was responsible for 70% of global annual N 2 O emissions [11,12]. As N 2 O is a powerful greenhouse gas with 298-fold greater global warming potential than CO 2 [2] and is also involved in the destruction of stratospheric ozone [13], numerous previous research focused on measuring N 2 O emissions under different N application rates [14][15][16]. The effect of eCO 2 on N 2 O emissions is receiving more attention, since it can address our current knowledge gap about soil feedback of global warming.…”

“…However, no consensus has been reached so far. The response of N 2 O emissions to eCO 2 has varied in different studies, where the duration of the CO 2 enrichment experiment and aboveground vegetation types were different [16][17][18].…”

“…Such increases in labile C supply, soil moisture, and lower aeration can cause higher N 2 O emission through enhanced denitrification, especially when soil nitrate N was high [18,19]. On the other hand, eCO 2 may promote plant N uptake or microbial N immobilization, which would in turn decrease soil N availability and, thus, N 2 O emissions [8,16,34]. The decomposition and mineralization of organic components are mediated by soil enzyme activities, which are highly sensitive to associated substrates and could reflect both the changes in concentrations and components of soil labile C and N [35].…”