SEEDLING EMERGENCE IN THE ROWAN (SORBUS-AUCUPARIA) FROM AN ALTITUDINAL GRADIENT

Seeds of the rowan were collected from an altitudinal gradient to allow seedling emergence, growth and dark respiration rates to be determined under standard conditions. Seed viability decreased with increase in altitude of seed source. Altitude of seed source also affected the length of low temperature treatment (2.degree. C) necessary to promote subsequent seedling emergence at 20.degree. C. Treatment for 6-12 wk produced maximum emergence in high altitude populations, whereas those from lower altitudes required a longer period of low temperature. Some seedling emergence during low temperature treatment was observed in the low altitude populations. Dark respiration rates of shoot bud tissue taken directly from the field showed a significant positive correlation with altitude. This contrasted with the respiration rate of seedlings grown under standard conditions in the laboratory which showed no such correlation, suggesting that the dark respiration rate is ultimately controlled by climatic variables rather than by intrinsic fixed differences between populations. The mean relative growth rate of the seedlings increased with increasing altitude of origin.