Relationship Between Morphological Adaptation to Grazing, Carbon Balance and Waterlogging Tolerance in Clones of Dactylis Glomerata L.

Summary Clonally‐propagated individuals of Dactylis glomerata L. derived from two contrasted habitats, respectively, moist soil with no grazing and drought‐prone soil under intense grazing, were tested for tolerance of waterlogging in soil culture. The clone of dry soil unexpectedly proved much more tolerant than the clone of moist soil. Measurements of 24 populations of D. glomerate grown in an experimental garden showed that the grazing pressure in the original habitat is reflected very strongly in the morphology of the garden‐grown plants. Adaptation to grazing comprises a short and narrow‐leaved, prolific tillering habit with production of very short inflorescences. Heavy grazing, or the cutting regime imposed in the waterlogging trial, is likely to do more damage to the upright, long‐leaved morphs of the ungrazed site. Measurements of carbon balance in intact plants and in defoliated tillers support this interpretation and also suggest that the larger oxygen consumption of the massive leaf bases of the ungrazed form might limit root penetration in oxygen deficient conditions. The greater length of roots in the dry soil clone is also discussed as a possible adaptation to water shortage in its cliff ledge habitat.