GROWTH, SHOOT PHENOLOGY AND PHYSIOLOGY OF DIVERSE SEED SOURCES OF BLACK SPRUCE .2. 23-YEAR-OLD FIELD TREES

Four sources of 23-year-old black spruce (Picea mariana (Mill.) B.S.P. ) from a provenance test at the Petawawa National Forestry Institute ( 46 degrees N, 77 degrees 30' W) were assessed for height growth, shoot phenology and seasonal gas exchange. The provenances were designated 7000 Yukon, 63 degrees 34' N, 135 degrees 55' W), 6979 (Alberta 52 deg rees 22' N, 115 degrees 15' W), 6908 (Ontario, 48 degrees 59' N, 80 de grees 38' W) and 6901 (Ontario, 45 degrees 10' N, 77 degrees 10' W). T rees of southern provenances (6901 and 6908) were considerably taller, and broke bud and ceased growth later than trees of northern provenan ces (6979 and 7000). In early spring, trees of northern provenances ha d higher net photosynthetic rates (P-n) than trees of southern provena nces (6908 and 6901). During midsummer, trees of Provenance 7000 gener ally had the highest P-n as a result of low rates of shoot dark respir ation (R(d)) Trees of northern provenances displayed an earlier autumn decline in P-n than trees of southern provenances. Provenance differe nces in growth, shoot phenology and physiology agreed well with result s from a greenhouse study of seedlings from the same provenances. We c onclude that the poor growth performance of trees of northern provenan ces in Ontario was associated with: (1) a short period of shoot growth , (2) a high rate of dry matter partitioning to roots, (3) low rates o f late-season P-n in response to decreasing photoperiod, and possibly, (4) a high rate of root R(d).