Abstract:

Fine root morphology can affect root absorption of nutrients and water from soil, and the morphology is not only controlled by root structure, but also by exterior environments. In this paper, root morphology variation of Fraxinus mandshurica seedlings in response to nitrogen concentration was investigated with a potting sand-cultured experiment with three nitrogen (N) level in a greenhouse. The changes of morphology in both total roots and the first three order roots, and anatomical properties under different N concentration treatments were examined respectively. The results showed that: 1) total root surface area, total root length and specific root length (SRL) increased significantly with increasing N supplied, however, mean diameter was higher in low N treatment than in control and high N treatments. These morphological indices in the first three order roots had the same patterns as total roots. The changes in root surface area and SRL of the first three order roots from low N to high N treatments were derived from integrated changes of their diameter and length. 2) The changes of diameter and length in the first three order roots with different N treatments were closely related to changes of their anatomical properties. Increasing cortical cell diameter and cortical thickness in transverse section at low N treatment resulted in larger diameter roots. In contrast, cortical cell diameter and cortical thickness were reduced in high N treatment, therefore, resulting in smaller diameter. In vertical section, root length increment from low N to high N treatments was possibly due to increasing cell numbers at long direction. These results suggested that variations of fine root morphology under different N treatments were closely related to root anatomical changes.

Key words: Fraxinus mandshurica, nitrogen treatment, root morphology, root anatomy