Annals of Botany 28: 251-270, 1964
© 1964 Annals of Botany Company
RESEARCH-ARTICLE |
Genetic Variation in the Utilization of Nitrogen by Ryegrass Species Lolium perenne and L.multiflorum
Welsh Plant Breeding Station Aberystwyth
The reaction of four ryegrass varieties (S. 22, S. 24, S. 101, and Melle) to differing degrees of nitrate stress was investigated. Plants supplied with inadequate N had low shoot/root ratios and were also characterized by high soluble carbohydrate and low crude-protein contents. Alleviating the stress by adding supplementary nitrate to the cultures rapidly reduced the soluble-carbohydrate content and increased the crude-protein percentage, but within the limits of the experiment shoot/root ratios were unchanged during resurgent growth.
The pattern of N utilization over a 9-day period following nitrate supplement depended on the degree of initial nitrate stress. Thus there was generally an immediate rise in the nitrate, amide, and 
-amino-N fractions of the leaves, but the effect was much more pronounced on plants which had been grown on low nutrition. From the general pattern of N distribution in the plant it was concluded that following nitrate reduction there was initial synthesis of -amino-N but that amide was also formed by primary synthesis. Differences between varieties were large! y a consequence of their differential rates of growth. The behaviour of Melle on low nutrition was, however, quite exceptional in that the yield of soluble-N was always greater than that of insoluble-N, this difference being largely due to a residual undetermined soluble-N fraction.
In a second experiment it was found that even within a bred variety (S. 24) genotypes varied in their efficiency of N utilization. Thus it was possible to obtain ryegrass plants with the same yield but different N-contents, or different yields for the same N-content. Efficiency was defined in terms of dry-weight increase per unit of N absorbed. Efficient plants (those with high yields and low N) were characterized by lower nitrate and higher -amino-N contents than inefficient ones so that a partial block in nitrate reduction is postulated in the latter. Although plants could be classified at all levels of nitrate nutrition, differences in yield were enhanced when nutritional nitrate was not limiting and under these conditions efficient genotypes also showed a greater final capacity for nitrate uptake.
Under the conditions of the experiment, the genotypic potentials for tiller production, yield, crude-protein content, and the content of soluble carbohydrates all showed a high degree of independence which suggests the possibility of simultaneous selection for all these traits.