The effect of nitrogen supply on root growth and development in sycamore and Sitka spruce trees

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Abstract
Sycamore ( Acer pseudoplatanus L.) and Sitka spruce ( Picea sitchensis (Bong.) Carr.) were grown in sand culture in glasshouses with two levels of N supplied with irrigation 1.0 (deficient) and 6.0 (sufficient) molNm −3 , all as NH 4 NO 3 . Providing trees with a sufficient N supply increased both their above ground growth and N content compared with the N deficient plants. Provision of the generous N supply also altered the distribution of growth between leaves and roots, with the N-deficient plants having a higher root:leaf or root:needle ratio than the well fertilized trees. Provision of a generous N supply stimulated root growth, especially at the later harvests, which was reflected mainly in growth of the tap root in sycamore. There was an increase in both root mass and root diameter with N supply. When the growth of white roots was monitored using a borescope, it was shown that there were significantly more new roots produced by the well-fertilized trees. The borescope data also showed detail of the bimodal seasonal pattern of root growth under high N in Sitka spruce which related to trends in nitrogen uptake.
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