Analysis of the Nitrogen Response of Leaf Extension in Lolium temulentum Seedlings

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Abstract
Lolium temulentum seedlings were grown on a nutrient medium containing NH4NO2 at 0, 0·1, 0·5, 1·0 and 4·3 mmoll−1 as the sole N source. Relative and absolute extension rates, maximal leaf size, duration of extension growth, rate of leaf appearance and plastochron index were determined from the parameters of Richards functions fitted to lengths of laminae measured at intervals after sowing. The final length of leaf I was relatively insensitive to N whereas mean relative extension rate was increased and duration of growth decreased with increasing NH4NO2 concentration. Leaves 2 and 3 enlarged progressively with N at concentrations up to 1·0 mmoll−1 but were unresponsive thereafter. There was no significant correlation between final length and mean relative extension rate for leaves 1 to 3. Leaves 4 to 6 continued to show increasing length beyond 1·0 mmoll−1 N and final length was significantly correlated with mean relative extension rate. Increasing N increased the rate of leaf appearance by decreasing the duration of leaf extension and plastochron. These results are discussed in relation to the control of leaf and N turnover.