Effect of nitrogen deficiency on photosynthesis and the partitioning of 14C-labelled leaf assimilate in unshaded and partially shaded plants of Lolium temulentum

The effect of a deficiency of applied nitrogen on the rate of leaf photosynthesis, and on the subsequent partitioning of ¹⁴C-labelled leaf assimilate between new leaf, stem, tillers and root, was investigated in single plants of Lolium temulentum L., grown normally in controlled environments, or grown with collars shading the base of the plant. The nitrogen deficiency reduced the rate of leaf photosynthesis, increased the retention of assimilate in the leaf, suppressed the export of assimilate to tillers, and generally increased the export of assimilate to roots and to new leaves. Shading the base of the plant generally had little effect on the rate of leaf photosynthesis, reduced the export of assimilate to roots, and increased the export of assimilate to new leaf and to the stem, which elongated when shading was imposed.