Seasonal nitrogen storage and remobilization in the forb Rumex acetosa

1. The contribution of N storage and remobilization to the vegetative and reproductive growth of the forb Rumex acetosa was quantified using N-15 labelling techniques with plants derived from semi-natural grasslands in Scotland. 2. The contribution of remobilized N to the total N in the new above-ground tissues was highest at the beginning of the growing season at 58%. New leaves and reproductive organs contained equal amounts of remobilized N. 3. During early vegetative growth, the taproot was the main source of remobilized N, whereas during reproductive growth, N was additionally remobilized from fine roots and leaves. 4. Free amino acids (mainly arginine and glutamine) and proteins were identified as the main storage compounds in the taproots. The protein pool did not show any seasonal variations that indicated the existence of a vegetative storage protein, indicating that such proteins are not a necessary component of N storage/remobilization in all species. 5. The ability to store and remobilize N provides a mechanism for growth in the spring when the availability of soil N is low, and means that growth depends upon environmental conditions during more than one year.