Root response to above-ground light quality - Differences between rhizomatous and non-rhizomatous clones of Festuca rubra

Root response to reduced red/far red ratio above ground was studied in an e xperiment with 12 vegetatively propagated clones of Festuca rubra, a rhizom atous grass species. A new method suitable for describing the node position within rhizome systems was developed. It uses a combination of development al and functional directions of ordering, adopting methods of topology. At each node the root structure was defined as consisting of three root types: unbranched, long branched and fine branched. Root system size was expresse d as the number and length of roots of these individual types. Rhizomatous and non-rhizomatous clones of Festuca rubra differed in the size and struct ure of their root systems and in the response to lowered red/far red light ratio. This response was caused more by the behaviour of the rhizomes than of the roots alone. In rhizomatous clones, the largest differences in root system structure were between the mother-nodes and the nodes on the rhizome s. The size of the root system also depended on the node position. Response to the red/far red ratio was clone specific only in some of the root param eters, especially in traits of unbranched roots at young nodes. The role of the three root morphotypes in the plant's ontogeny, nutrient uptake and ab ility to cope with environmental heterogeneity both above- and below ground , is discussed.