EARLY SELECTION FOR DROUGHT TOLERANCE AND RELATIONSHIP TO DRY-WEIGHT PARTITIONING IN BLACK SPRUCE FAMILIES

Black spruce (Picea mariana [Mill.] B.S.P.) families varied in growth rate on drier but not on moister sites as a result of water stress. To determine the relationship between growth and its partitioning, and d rought tolerance, seedlings dry weight of 7 full-sib black spruce fami lies was compared for 2 growing seasons under well-watered conditions and drought in a nursery with that of 16-yr field height growth on dry and moist sites. Family variation in dry weight partitioning among ro ots, shoots, stems, and needles was also compared. Family ranks in see dling total dry weight under droughted conditions correlated significa ntly with family ranks in field height growth after 16 yr on the dry, but not moist sites. Two families (22 and 43) exhibited superior growt h rates under drought, but not well-watered conditions compared with 3 other families (25, 46, and 50), whose growth declined significantly under drought stress. The greater total dry weight growth of families 22 and 43 under drought was the result of sustained leaf growth. By co ntrast, less vigorous families 25, 46, and 50 allocated more dry weigh t to the roots at the expense of needle and stem growth when droughted . Families did not differ in dry weight partitioning under well-watere d conditions, however. These early growth and partitioning responses t o drought stress may therefore provide criteria for selecting drought tolerant, faster growing genotypes for drier, but not moister, sites.