Seasonal nitrogen partitioning in Japanese cedar (Cryptomeria japonica, D. Don) tissues

Aims Nitrogen withdrawal from senescing leaves in evergreen trees is assumed to be stored mainly in the remaining leaves at the end of the growing season. However, there is evidence that roots as well as stem tissues play a significant role in nitrogen and other nutrients storage. Therefore, the objective of this study is to clarify the seasonal nitrogen cycle in Japanese cedar trees in order to elucidate its N storage strategy. Methods N content, isotope ratio and amino acids content were measured in coarse roots, sapwood, leaves (separated by age), litter and buds along the growing season. Results Nitrogen content increased from the shoot growth to the post-abscission period with younger leaves storing more N than older ones. N from senescent leaves was reabsorbed to roots in October and to sapwood and the remaining leaves in November accounting for only 5% of whole-tree stored N. No temporal N isotopic fractionation was observed in plant tissues except for leaf enrichment during storage. The variation of amino acids in leaf tissues explained internal N transport. Conclusions Japanese cedar trees reabsorbed leaf N and soil N in the pre-abscission period and stored most N in roots (54%) and sapwood (20%) followed by leaves (18%) and branches (8%), respectively.