EGU2020-19445
https://doi.org/10.5194/egusphere-egu2020-19445
EGU General Assembly 2020
© Author(s) 2022. This work is distributed under
the Creative Commons Attribution 4.0 License.

NO3- uptake and C exudation – do plant roots stimulate or inhibit denitrification?

Pauline Sophie Rummel1, Reinhard Well2, Birgit Pfeiffer1,3, Klaus Dittert1, Sebastian Floßmann4, and Johanna Pausch4
Pauline Sophie Rummel et al.
  • 1Plant Nutrition and Crop Physiology, Department of Crop Science, University of Göttingen, Germany (pauline.rummel@uni-goettingen.de)
  • 2Thünen Institute of Climate-Smart Agriculture, Federal Research Institute for Rural Areas, Forestry and Fisheries, Braunschweig, Germany
  • 3Institute of Microbiology and Genetics, Department of Genomic and Applied Microbiology, University of Göttingen, Germany
  • 4Agroecology, Faculty for Biology, Chemistry, and Earth Sciences, University of Bayreuth, Germany

Growing plants affect soil moisture, mineral N and organic C (Corg) availability in soil and may thus play an important role in regulating denitrification. The availability of the main substrates for denitrification (Corg and NO3-) is controlled by root activity and higher denitrification activity in rhizosphere soils has been reported. We hypothesized that (I) plant N uptake governs NO3- availability for denitrification leading to increased N2O and N2 emissions, when plant N uptake is low due to smaller root system or root senescence. (II) Denitrification is stimulated by higher Corg availability from root exudation or decaying roots increasing total gaseous N emissions while decreasing their N2O/(N2O+N2) ratios.

We tested these assumptions in a double labeling pot experiment with maize (Zea mays L.) grown under three N fertilization levels S / M / L (no / moderate / high N fertilization) and with cup plant (Silphium perfoliatum L., moderate N fertilization). After 6 weeks, all plants were labeled with 0.1 g N kg-1 (Ca(15NO3)2, 60 at%), and the 15N tracer method was applied to estimate plant N uptake, N2O and N2 emissions. To link denitrification with available C in the rhizosphere, 13CO2 pulse labeling (5 g Na213CO3, 99 at%) was used to trace C translocation from shoots to roots and its release by roots into the soil. CO2 evolving from soil was trapped in NaOH for δ13C analyses, and gas samples were taken for analysis of N2O and N2 from the headspace above the soil surface every 12 h.

Although pots were irrigated, changing soil moisture through differences in plant water uptake was the main factor controlling daily N2O+N2 fluxes, cumulative N emissions, and N2O production pathways. In addition, total N2O+N2 emissions were negatively correlated with plant N uptake and positively with soil N concentrations. Recently assimilated C released by roots (13C) was positively correlated with root dry matter, but we could not detect any relationship with cumulative N emissions. We anticipate that higher Corg availability in pots with large root systems did not lead to higher denitrification rates as NO3- was limited due to plant uptake. In conclusion, plant growth controlled water and NO3- uptake and, subsequently, formation of anaerobic hotspots for denitrification.

How to cite: Rummel, P. S., Well, R., Pfeiffer, B., Dittert, K., Floßmann, S., and Pausch, J.: NO3- uptake and C exudation – do plant roots stimulate or inhibit denitrification?, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-19445, https://doi.org/10.5194/egusphere-egu2020-19445, 2020.

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