Fluxes and mechanisms of permanent nitrogen removal and N2O production in a heavy nitrogen loaded regions of China
Zusammenfassung der Projektergebnisse
The Yangtze River Delta region is a heavy N loading region with intensive agriculture where excess of reactive nitrogen (Nr) causes various eco-environmental problems. Gaseous losses as N2 in the atmosphere are considered an important Nr removal process, but due to methodical difficulties, this could not be confirmed previously. The overall goal of the project was to establish and further develop methods to quantify N2 fluxes at various scales and use those to elucidate the production pathways of N2 in different land-use type areas of the Yangtze Delta Region in China. Research was accomplished in a collaborative project by Thünen Institute of Climate-Smart Agriculture and the Institute of Ssoil Science of the Chinese Academy of Science (CAS). Specific tasks of the Thünen part were to establish a robotic incubation system for N2 and greenhouse gas flux measurement (ROFLOW) in CAS and Thünen labs, to investigate key factors controlling denitrification rate and its N2O/(N2O+N2) ratio in soils from Yangtze Delta Region, to distinguish N2O producing processes using several stable isotope approaches, and to investigate effects of rhizosphere processes and N forms on N2O production and reduction to N2. After establishing the ROFLOW system at Thünen and CAS labs, eight lab incubation experiments were conducted using ROFLOW to study the effect of labile C, nitrogen rate/form, moisture, rhizosphere processes and O2 level on denitrification and the associated N2O/(N2O+N2) ratio in selected three soils originating from different land use systems. From the results, we conclude that straw amendment in moist soils enhances soil denitrification rate and may trigger gaseous N losses. Specifically shortly after rewetting or organic matter amendment denitrification produces almost solely N2O with little NO and N2 emissions from straw amended soils, when soil NO3-content is high. All of our experiments suggests that straw application itself, even at very high rates, does not directly affect the product stoichiometry of denitrification (N2O/(N2O+N2) product ratio). On the other hand, after a long moist period with stabilized microbial activity, even high level of NO3- does not inhibit N2O reduction to N2.Thus, we suggest that in agricultural systems where large amount of organic plant residues are incorporated into soil, risk of N2O emissions after rewetting events can be minimized by keeping soil NO3- concentrations under site-specific threshold values. First data of ROFLOW with plants indicated that in moist soils with a moderately high NO3- content, the root system of an actively growing plant stimulates greater losses of both N2O and N2 through denitrification but without affecting the N2O/(N2O+N2) product ratio. Using isotopocule values of emitted N2O, we investigated the relative contributions of fungal and bacterial denitrification to N2O emission. Shortly after rewetting, N2O from bacterial denitrification was the primary source of emitted N2O under given experimental conditions with a clear shift to fungal N2O over time. Among the three soils tested, the paddy soil exhibited the highest share of fungal denitrification (about half of the emitted N2O) whereas vegetable and vineyard soils appeared to be dominated by bacterial denitrification. Results from joint work of CAS an Thünen on intact soil core incubations from field sites and isotopocule values from field flux studies is still under evaluation. The same applies to the final evaluation of the multi-labelling experiment to identify multiple N2O pathways of the vegetable soil (joint with collaboration partner Prof. C. Müller) and of the site-specific calibration of the isotopocule approach (joint with collaboration partner Dr. D. Lewicka-Szczebak).
Projektbezogene Publikationen (Auswahl)
- (2018) Denitrification in shallow groundwater below different arable land systems in a high nitrogen-loading region. J Geophys Res Biogeosci 123(3):991-1004
Zhou W, Ma Y, Well R, Wang H, Yan X
(Siehe online unter https://doi.org/10.1002/2017JG004199) - (2018) Interaction of straw amendment and soil NO3‘ content controls fungal denitrification and denitrification product stoichiometry in a sandy soil. Soil Biol Biochem 126:204-212
Senbayram M, Well R, Bol R, Chadwick DR, Jones DL, Wu D
(Siehe online unter https://doi.org/10.1016/j.soilbio.2018.09.005) - (2018) Straw amendment with nitrate-N decreased N2O/(N2O+N2) ratio but increased soil N2O emission: A case study of direct soil-born N2 measurements. Soil Biol Biochem 127:301-3
Wu D, Wei Z, Well R, Shan J, Yan X, Bol R, Senbayram M
(Siehe online unter https://doi.org/10.1016/j.soilbio.2018.10.002) - (2020) Regulation of the product stoichiometry of denitrification in intensively managed soils. Food Energy Secur 9(4):e251
Wei Z, Shan J, Chai Y, Well R, Yan X, Senbayram M
(Siehe online unter https://doi.org/10.1002/fes3.251) - (2020) Rhizosphere processes in nitrate-rich barley soil tripled both N2O and N2 losses due to enhanced bacterial and fungal denitrification. Plant Soil 448:509-522
Senbayram M, Well R, Shan J, Bol R, Burkart S, Jones DL, Wu D
(Siehe online unter https://doi.org/10.1007/s11104-020-04457-9)
