EGU General Assembly 2022
© Author(s) 2022. This work is distributed under
the Creative Commons Attribution 4.0 License.

The role of maize root exudates to availability of N source in different forms in top- and subsoils

Juanjuan Ai1,2, Callum Banfield1,2, Guodong Shao2, Kazem Zamanian3, Sandra Spielvogel4, and Michaela Dippold1,2
Juanjuan Ai et al.
  • 1Biogeochemistry of Agroecosystems, Department of Crop Sciences, University of Göttingen, Göttingen, Germany (
  • 2Geo-Biosphere Interactions Department of Geosciences, University of Tübingen, Tübingen, Germany
  • 3Department of Soil Science of Temperate Ecosystems, University of Göttingen, Göttingen, Germany
  • 4Institute of Plant Nutrition and Soil Science, Christian-Albrecht-University of Kiel, Kiel, Germany

Nitrogen (N) availability is a main constraint to plant productivity, especially when vegetation relies largely on subsoils, which contain considerable N resources but in low availability. Rhizodeposition can promote N cycling by stimulating microbial growth and activity and thus induces the release of mineral-bound nutrients and accelerates decomposition of soil organic matter (SOM). However, many specific processes how root exudates interact with distinct N forms altering their subsoil mobilization still remain unclear. We hypothesize that the lower microbial activity but higher sorption capacity of subsoils induces subsoil-specific N dynamics. To disentangle this, we added four N sources (free NH4+, sorbed NH4+, urea and plant residues with identical total N content) into top-and subsoils. We quantified microbial processes regulating mineral and organic N availability in top-and subsoils by simulating rhizosphere condition via application of collected root exudates in a well-controlled microcosm experiment. Our results showed that neither growth of the total microbial community, nor shift in the community composition occurs based on maize root exudate amendment resembling a daily exudation amount. However, we observed a clear increase in microbial activity and activation of organic nutrient mobilizing mechanisms (e.g. enzyme activation), which was in most cases higher in sub- than in topsoils. This suggests that root exudates may not be of highest relevance for topsoil nutrient mobilization. In contrast, high root exudation is of much higher relevance for crops, which aim to mobilize a significant proportion of their nutrients from subsoils. We could demonstrate that subsoil communities were well capable of using litter-derived N, especially if root exudates accelerate overall activity and N cycling in subsoils. N incorporated from plant litter is successively recycled in microbial bio-and necromass following the initial degradation. Consequently, if breeding for deep-rooting crops with nutrient uptake from subsoils shall be promoted in the future, it is essential to ensure that these crops deep roots have a high root exudation to activate the highly C limited microbial communities of the subsoil.

How to cite: Ai, J., Banfield, C., Shao, G., Zamanian, K., Spielvogel, S., and Dippold, M.: The role of maize root exudates to availability of N source in different forms in top- and subsoils, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-4304,, 2022.

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