Environmental and intrinsic regulation of phosphorus acquisition, partitioning, storage, and mobilization in beech and poplar trees

Phosphorus is an essential macronutrient for growth and development of plants due to its function in DNA and RNA for inheritance, in free nucleotides for energy transfer, in phospholipids as membranes components as well as in sugar phosphates for carbon metabolism including signalling and regulation. Because of its low availability in many forest soils, efficient uptake, use and cycling in plants and ecosystems are required. Furthermore, these processes have to be adapted to the changing phosphorus demand throughout the annual growth cycle and to environmental changes like increasing N-deposition into ecosystems. The present project aims (i) to characterize the influence of N-deposition on P-cycling in beech trees, (ii) to identify drivers and processes that control P-cycling within the whole tree with special emphasis on N-deposition and, (iii) to detect intrinsic factors that control P-acquisition at varying N-nutrition. N-deposition into temperate forest ecosystems strongly influences nitrogen cycling in trees und affects N:P ratios. In the present project the effects of N-deposition on P-cycling in poplar and beech trees will be investigated under controlled conditions and in the field at two contrasting core field sites of the SPP; namely Lüss with low soil P and thus expected to be a recycling ecosystem and Bad Brückenau as an example for an acquiring ecosystem with high plant available P. Beech seedlings from the Conventwald which were found to be P-acquiring (field experiments performed during the first phase of the SPP) will be used in experiments under controlled conditions to induce P-deficiency by N-fertilization. Poplar will be investigated as a model tree species that allows for molecular analyses to identify intrinsic factors controlling P-cycling during the annual growth cycle as well as after N-deposition induced P-deficiency. Furthermore, poplar will be used to work on systemic signals that control P-acquisition. In all experiments P-acquisition of Pi and Porg (ATP and glucose-6-P) and P-pools, i.e. Ptot and Pi, will be determined. Two years after starting N-, P- and NxP-fertilization experiments, adult beech trees from the fertilization plots of the field sites Lüss and Bad Brückenau will be analysed regarding P-acquisition and P-cycling during the annual growth cycle.