Macropore effects on phosphorus acquisition by wheat roots – a rhizotron study
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Background and aims
Macropores may be preferential root pathways into the subsoil. We hypothesised that the presence of macropores promotes P-uptake from subsoil, particularly at limited water supply in surface soil. We tested this hypothesis in a rhizotron experiment with spring wheat (Triticum aestivum cv. Scirocco) under variation of fertilisation and irrigation.
Rhizotrons were filled with compacted subsoil (bulk density 1.4 g cm−3), underneath a P-depleted topsoil. In half of these rhizotrons the subsoil contained artificial macropores. Spring wheat was grown for 41 days with and without irrigation and 31P–addition. Also, a 33P–tracer was added at the soil surface to trace P-distribution in plants using liquid scintillation counting and radioactive imaging.
Fertilisation and irrigation promoted biomass production and plant P-uptake. Improved growing conditions resulted in a higher proportion of subsoil roots, indicating that the topsoil root system additionally promoted subsoil nutrient acquisition. The presence of macropores did not improve plant growth but tended to increase translocation of 33P into both above- and belowground biomass. 33P–imaging confirmed that this plant-internal transport of topsoil-P extended into subsoil roots.
The lack of penetration resistance in macropores did not increase plant growth and nutrient uptake from subsoil here; however, wheat specifically re-allocated topsoil-P for subsoil root growth.
KeywordsMacropores 33P–imaging P-uptake Rhizotrons Subsoil Wheat
We would like to thank Dr. H. Hüging of the Department of Crop Science of the University of Bonn for providing access and support in sampling at the long-term fertilisation trial at Dikopshof, and also we gratefully acknowledge the staff at the Institute IBG-2: Plant Sciences at Forschungszentrum Jülich GmbH for technical support in maintaining the growth chamber. Further, we would like to thank B. Überbach of the Department of Plant Nutrition of the University of Bonn for support in the extractions of non-radioactive plant material and A. Kubica of the Institute of Bio- and Geosciences – Agrosphere (IBG-3) at Forschungszentrum Jülich GmbH for support in the handling and extraction of the radioactive material. Finally, we would like to thank Dr. T. Kautz and three anonymous reviewers for helpful comments and improvements on the manuscript. The 33P-imigaing was funded by the BonaRes framework of the German Federal Ministry of Education (Bundesministerium für Bildung und Forschung, BMBF) within the project InnoSoilPhos. All other work was funded by the German Research Foundation (Deutsche Forschungsgemeinschaft, DFG) within the framework of the research consortium DFG PAK 888.
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