Seasonal phosphorus and nitrogen cycling in four Japanese cool-temperate forest species

Purpose: In plant-soil systems, phosphorus partitioning during the annual cycle related to nitrogen partitioning remains largely unknown. The present study aims at assessing the soil-plant P allocation patterns of four tree species along four phenological stages and its relationship with tissues and soil N concentrations. Methods: Cryptomeria japonica, Larix kaempferi, Fagus crenata and Robinia pseudoacacia trees were selected to sample coarse roots, sapwood, foliage, litter and soil during four phenological stages where total and Olsen extractable P and nitrogen content were measured respectively. Results: Intra- and inter plant tissue nitrogen correlated well with phosphorus during the four phenological stages, especially root nitrogen. Fagus and Robinia were phosphorus limited, Larix was nitrogen limited and Cryptomeria co-limited. All species reabsorbed phosphorus and nitrogen from foliage prior to leaf abscission and stored nitrogen in roots and sapwood. Phosphorus storage was solely found in sapwood of Robinia. Soil dissolved ammonium correlated positively with nitrogen reabsorption efficiency during the green leaf stage, while single soil nutrient variables did not correlate with phosphorus reabsorption efficiency. Conclusions: Plant tissues nitrogen partitioning correlated well with their respective phosphorus partitioning and the increase of soil NH4+ correlated positively with nitrogen reabsorption efficiency, regardless of tree species during the green leaf stage. The results of this study show the intricate relationship that exists between nitrogen and phosphorus in the soil-plant continuum as well as the tree species specific internal cycling of these nutrients.