EGU21-1223
https://doi.org/10.5194/egusphere-egu21-1223
EGU General Assembly 2021
© Author(s) 2022. This work is distributed under
the Creative Commons Attribution 4.0 License.

Nitrate and water uptake, rather than rhizodeposition, control denitrification in the presence of growing plants

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

The main prerequisites for denitrification are availability of nitrate (NO3-) and easily decomposable organic substances, and oxygen deficiency. Growing plants modify all these parameters and may thus play an important role in regulating denitrification. Previous studies investigating plant root effects on denitrification have found contradictive results. Both increased and decreased denitrification in the presence of plants have been reported and were associated with higher Corg or lower NO3- availability, respectively. Accordingly, it is still unclear whether growing plants stimulate denitrification through root exudation or restrict it through NO3- uptake. Furthermore, reliable measurements of N2 fluxes and N2O/(N2O+N2) ratios in the presence of plants are scarce.

Therefore, we conducted a double labeling pot experiment with either maize (Zea mays L.) or cup plant (Silphium perfoliatum L.) of the same age but differing in size of their shoot and root systems. The 15N gas flux method was applied to directly quantify N2O and N2 fluxes in situ. To link denitrification with available C in the rhizosphere, 13CO2 pulse labeling was used to trace C translocation from shoots to roots and its release by roots into the soil.

Plant water uptake was a main factor controlling soil moisture and, thus, daily N2O+N2 fluxes, cumulative N emissions, and N2O production pathways. However, N fluxes remained on a low level when NO3- availability was low due to rapid plant N uptake. Only when both N and water uptake were low, high NO3- availability and high soil moisture led to strongly increased denitrification-derived N losses.

Total CO2 efflux was positively correlated with root dry matter, but there was no indication of any relationship between recovered 13C from root exudation and 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 limiting denitrification due to plant N uptake. Overall, we conclude that root-derived C stimulates denitrification only when soil NO3- is not limited and low O2 concentrations enable denitrification. Thus, root-derived C may stimulate denitrification under small plants, while N and water uptake become the controlling factors with increasing plant and root growth.

How to cite: Rummel, P. S., Well, R., Pfeiffer, B., Dittert, K., Floßmann, S., and Pausch, J.: Nitrate and water uptake, rather than rhizodeposition, control denitrification in the presence of growing plants, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-1223, https://doi.org/10.5194/egusphere-egu21-1223, 2021.

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