Trace gas fluxes of CO<sub>2</sub>, CH<sub>4</sub> and N<sub>2</sub>O in a permanent grassland soil exposed to elevated CO<sub>2</sub> in the Giessen FACE study

Abstract

Abstract. Long-term field observations showed that N 2 O fluxes observed shortly after N application were not significantly affected by elevated CO 2 in the Giessen Free Air Carbon dioxide Enrichment (FACE) study. To further investigate this unexpected result a 15 N tracer study was carried out under controlled conditions where in parallel treatments either the NH The N 2 O production processes were identified by a twosource model. Results showed that N 2 O must have also been produced by a third source -possibly related to organic N transformation -which was stimulated by elevated CO 2 . Soil CO 2 fluxes were approximately 20 % higher under elevated CO 2 than soil from ambient but the differences were not significant. CH 4 oxidation rates were on average −1.75 ng CH 4 -C g −1 h −1 in the elevated and −1.17 ng CH 4 -C g −1 h −1 in the ambient indicating that elevated CO 2 increased the CH 4 oxidation by 49 % compared to ambient CO 2 under controlled conditions. N fertilization increased CH 4 oxidation by 3-fold in both CO 2 treatments. CO 2 did not have any significant effect on DEA while total denitrification and N 2 -to-N 2 O ratios increased by 36 and 33 %, respectively. The results indicate that shortly after N applicationCorrespondence to: M. Kaleem Abbasi (kaleemabbasi@yahoo.com) elevated CO 2 must have stimulated both the N 2 O production and reduction to N 2 to explain the increased N 2 -to-N 2 O ratio and at the same time explain the non-responsiveness of the N 2 O emissions. Thus, the observed variation of the CO 2 effect on N 2 O emissions throughout the year is possibly governed by the dynamics of the N 2 O reductase activity.

Warming-Induced Stimulation of Soil N2O Emissions Counteracted by Elevated CO2 from Nine-Year Agroecosystem Temperature and Free Air Carbon Dioxide Enrichment

“…The sporadic studies about the impacts of increased CO 2 levels on soil N 2 O emission pathways have mainly focused on nonagricultural ecosystems (Table S3). ,,− For instance, the doubling of N 2 O emissions under elevated CO 2 in the Giessen grassland FACE has been demonstrated to be the result of an increase in incomplete denitrification and therefore an increased N 2 O/N 2 emission ratio . In nonagricultural ecosystems, CO 2 effects on soil N 2 O emissions have been influenced by N deposition .…”

Functional Diversity and CO2 Emission Characteristics of Soil Bacteria during the Succession of Halophyte Vegetation in the Yellow River Delta

“…Global warming is a serious environmental issue that the world is currently dealing with [1], and it is primarily caused by an increase in greenhouse gases such as carbon dioxide (CO 2 ), methane (CH 4 ), and nitrous oxide (N 2 O) in the atmosphere [2]. According to the IPCC (2021), CO 2 is the most significant greenhouse gas, and an increase in its concentration causes the greenhouse effect, which is the primary contributor to climate change.…”