Abstract
Less attention has been given to soil enzymes that contribute to beneficial rhizosphere interactions in intercropping systems. Therefore, we performed a field experiment by growing faba bean, lupine, and maize in mono and mixed cultures in a moderately fertile soil. We measured shoot biomass and the kinetic parameters (maximal velocity (Vmax) and Michaelis-constant (Km)) of three key enzymes in the rhizosphere: Leucine-aminopeptidase (LAP), β-1,4-N-acetylglucosaminidase (NAG), and phosphomonoesterase (PHO). Faba bean benefitted in mixed cultures by greater shoot biomass production with both maize and lupine compared to its expected biomass in monoculture. Next, LAP and NAG kinetic parameters were less responsive to mono and mixed cultures across the crop species. In contrast, both the Vmax and Km values of PHO increased in the faba bean rhizosphere when grown in mixed cultures with maize and lupine. A positive relative interaction index for shoot P and N uptake for faba bean showed its net facilitative interactions in the mixed cultures. Overall, these results suggest that over-productivity in intercropping is crop-specific and the positive intercropping effects could be modulated by P availability. We argue that the enzyme activities involved in nutrient cycling should be incorporated in further research.

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Acknowledgments
We thank Thomas Niemeyer, Christoph Stegen, Vladimir Vakhtinskii, Pola Rief, Laura Störzer, Kiwii, Hannes Schempp, Johanna Wille, and Mira Hesselman for field assistance. This research was financed by the BonaRes Soil Sustainability Program of the German Ministry of Education and Research (BMBF) within the ‘INPLAMINT- Increasing agricultural nutrient-use efficiency by optimizing plant-soil-microorganisms interactions’ project with the grant number: 031B0508H. The contribution of Evgenia Blagodatskaya was through and Michaela Dippold was funded via the Robert-Bosch foundation (Junior Professorship 2017). We would like to thank anonymous reviewer and editor for their insightful comments and suggestions to improve the quality of this research. Open Access funding enabled and organized by Projekt DEAL.
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Highlights
• Intercropping effects on yield advantages are crop species specific.
• We measured kinetic parameters of three important enzymes in the rhizospheres of individual crop species in both mono and mixed cultures.
• In moderately nitrogen enriched soils, phosphorus becomes important nutrient element, involved in nutrient facilitation.
• Positive relative interaction index for faba bean when intercropped with either lupine or maize showed net facilitative interactions.
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Kumar, A., Blagodaskaya, E., Dippold, M.A. et al. Positive intercropping effects on biomass production are species-specific and involve rhizosphere enzyme activities: Evidence from a field study. Soil Ecol. Lett. 4, 444–453 (2022). https://doi.org/10.1007/s42832-021-0108-0
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DOI: https://doi.org/10.1007/s42832-021-0108-0
Keywords
- Enzyme kinetic parameters
- Phosphorus mobilization
- Nitrogen fixation
- Niche complementarity
- Biomass increase
- Relative interaction index