The accumulation and storage of nitrogen by herbaceous plants


Dr P. Millard, Department of Soil Fertility, The Macaulay Land Use Research Institute, Craigiebuckler, Aberdeen AB9 2QJ, U.K.


Abstract Accumulation of nitrogen (N) by plants in response to N supply outstripping demand is contrasted with storage of N, which implies that N in one tissue can be reused for the growth or maintenance of another. Storage can, therefore, occur in N-deficient plants; accumulation can not. The consequence of accumulation and storage of N is considered, particularly in relation to the reproductive growth of annual plants, which can often use a great deal of stored N. Nitrate and proteins are the forms of N most often stored in vegetative tissues and, quantitatively, ribulose 1,5-bisphosphate carboxylase/oxygenase is often the most important protein store. While storing nitrate will be less costly to the plant in terms of energy, protein stores offer several possible advantages. These advantages are (i) maximizing the potential for carbon assimilation, (ii) avoiding problems with the regulation of leaf turgor and (iii) allowing the reduction on nitrate to occur in the young, fully illuminated leaf.