Impacts of N/P inputs on organic P dynamics and P status in soils and plants along a nutrient gradient

• Applicants: Professorin Dr. Yvonne Oelmann; Dr. Thomas Pütz
• Subject Area: Soil Sciences
• Term: from 2013 to 2021
• Project identifier: Deutsche Forschungsgemeinschaft (DFG) - Project number 241216797

Atmospheric nitrogen (N) deposition has been shown to affect N cycling in forests with feedbacks on the phosphorus (P) cycle. Therefore, the main objective of the 2nd phase of the SPP 1685 priority program is to investigate the importance of soil organic matter turnover on P cycling under environmental change. This will be tested in a common field experiment installed in Lüss and Bad Brückenau studying the effect of N, P and N+P additions on N and P dynamics and forest nutrition. Major effects are expected in Lüss, the P-limited ecosystem, which would eventually shift from a recycling to an acquiring strategy.The objectives of our joint proposal (Group of Plant Nutrition, ETH Zurich; Group of Geoecology, University of Tübingen; Group of Environmental Sensing and Monitoring, FZ Jülich) are to determine which and to which extent soil biological processes in the forest ecosystem are affected by mineral N and P additions and how this further translates into plant nutrition over the three years of the second phase of the SPP 1685. We plan to extend the set of field sites because of the unique opportunity to study the fate of fertilizer-P by radioactive isotopes (P-32, P-33) under outdoor conditions in a forest at the FZ Jülich (intermediate in terms of soil P fractions as compared to Lüss and Bad Brückenau). Our hypotheses are that after mineral fertiliser additions, the distribution of inorganic and organic P forms in soils will change, more in Lüss than in Jülich and Bad Brückenau. The mineralogy and initial P status of the soils will also be determinant factors for the changes. As a result, the source for plant P (and N) nutrition will differ between Lüss, Jülich, and Bad Brückenau. Processes in soil and fluxes in soil and between plants and soil will also be affected in the short term (3 years of the project), most likely because of an increased organic matter turnover. We will use microbiological tools and P-31 NMR analysis together with stable and radioactive isotope techniques. Using these complementary tools we will be able to quantify soil and plant P pools, characterize organic P forms, assess soil microbial community structure harbouring phosphatase genes, quantify fluxes of P between pools in soils and plants, and identify the contribution of different sources for plant nutrition of exemplary forest ecosystems subject to N and P additions.

• DFG Programme: Priority Programmes
• Subproject of: SPP 1685: Ecosystem Nutrition: Forest Strategies for Limited Phosphorus Resources
• International Connection: Switzerland
• Partner Organisation: Schweizerischer Nationalfonds (SNF)
• Co-Investigator: Professor Dr. Emmanuel Frossard