WITHIN POPULATION GENETIC DIFFERENTIATION IN TRAITS AFFECTING CLONAL GROWTH - FESTUCA-RUBRA IN A MOUNTAIN GRASSLAND

Festuca rubra, a clonal grass of mountain grasslands, possesses a cons iderable variability in traits related to spatial spreading (rhizome p roduction, length and branching; tussock architecture). Since these tr aits highly influence the success of the species in a spatially hetero geneous system of grasslands, a combined field and growth chamber appr oach was adopted to determine the within-population variation in these parameters. Clones were sampled in a mountain grassland (The Krkonose Mts., Czech Republic); the environment (mean neighbour density) of in dividual clones varied highly. Before the clones were collected, shoot demography and tussock architecture within these clones were recorded in the field for four seasons. Their clone identity was determined us ing DNA RAPD. Vegetatively propagated plants from these clones were cu ltivated in a common garden experiment to demonstrate variation in tus sock growth and architecture. Their response to change in red/far red light ratio was determined in the growth chamber. Highly significant v ariation among clones was found in almost all parameters. In the commo n garden, the clones differed in tussock growth (mean tillering rate), architecture (mean shoot angle, mean tussock density) and proportion of flowering shoots. In the growth chamber, both the aboveground param eters and parameters of the rhizome system were strongly affected by r ed/far red ratio; among-clone variation was also almost always signifi cant. The genotype x environment interaction was significant for tille ring rate and rhizome architecture. The structure of the rhizome syste m (which is the major component of clonal spread in space) is a comple x result of several components whose inter-clone variations differ: (i ) genetically determined mean rhizome system sizer (ii) overall plasti city in rhizome system size (with no significant genetic variation in plasticity), and (iii) genetically determined plasticity in rhizome ar chitecture. Because of the variation in plasticity in rhizome architec ture, some clones seemed to possess the ability to exploit a favourabl e habitat patch by producing short branches when there; whereas the re maining clones appeared to possess only a simple escape mechanism from unfavourable patches. Environmental variation in the light levels in the studied grassland is fine grained; horizontal growth rates of F. r ubra are sufficient to make genets experience different patches in the ir lifetime. The high variation in both, genotype means and plasticiti es is likely to be due to selection early in genet life in an environm ent which is heterogeneous at a fine scale.