Abstract
Lolium perenne L. (c.v. Magella) plants were grown under three nutrient treatments for six weeks and then defoliated to test the hypothesis that for their regrowth they could acquire N equally well irrespective of N distribution. Two different N levels were applied; uniform level 1 N (U1), uniform level 2 (U2) and heterogeneous level 2 (H2). A system where the nutrient patch could be applied without barriers to root growth was adopted. A single defoliation to 4 cm height resulted in a reduction in tillering, biomass increment and N uptake at 3 weeks after defoliation. Root growth was reduced by defoliation under all N treatments. Defoliation was found to reduce the proportion of N in the shoots which was derived from root uptake from 7 to 14 days. At 21 days this effect was significant for the plants with a heterogeneously distributed supply only. By the end of the regrowth period, the undefoliated plants from H2 had a shoot biomass and N content equal to that of plants receiving the same total N but supplied homogeneously (U2). However, defoliation reduced the ability of the plant to acquire N from the patch. No preferential root growth was measured into the N-rich patch, but an increased root diameter within the patch was found. Root diameter was reduced by defoliation, coinciding with a reduction in concentration of N in the root tissue. As a result of the increased sink strength of the growing leaves after defoliation, the roots may become a source of carbon and also nitrogen. These responses to an N-rich patch under defoliation could alter a plant's competitive balance in a mixed sward.
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Mackie-Dawson, L.A. Nitrogen uptake and root morphological responses of defoliated Lolium perenne (L.) to a heterogeneous nitrogen supply. Plant and Soil 209, 111–118 (1999). https://doi.org/10.1023/A:1004534609280
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DOI: https://doi.org/10.1023/A:1004534609280