CLOSE ASSOCIATION OF RGR, LEAF AND ROOT MORPHOLOGY, SEED MASS AND SHADE TOLERANCE IN SEEDLINGS OF 9 BOREAL TREE SPECIES GROWN IN HIGH AND LOW-LIGHT

1, To test hypotheses concerning adaptation and acclimation of tree sp ecies to shaded habitats wt determined the growth, biomass partitionin g and morphology of seedlings of nine near-boreal tree species in high - and low-light greenhouse environment (25 and 5% of full sunlight, re spectively), comparable to sunlit gap and shaded microsites in boreal forests. The species differ widely in shade tolerance, seed size and l eaf life span. 2, In low Light, all species allocated proportionally m ore biomass to stems and less to roots, but the same to foliage, compa red with the high-light environment. At a common size, all species had finer leaf morphology (higher specific leaf area, SLA) but coarser ro ot morphology (lower specific root length, SRL) in low than high light . From a whole plant perspective, all species enhanced leaf area per u nit plant mass (leaf area ratio, LAR) in low light and root length per unit plant mass (root length ratio, RLR) in high light. 3, Shade-into lerant deciduous species had higher RGR, SLA and SRL than larger seede d evergreens: ranking from Populus, Betula and Larix spp., then to fiv e evergreen Pinus, Picea and Thuja spp., which were generally comparab le in these traits, there were no changes in growth rankings of specie s between high- and low-light environments, nor consistent differences among species in biomass partitioning. Hence, species differences in leaf and root morphology (SLA; SRL) drove whole plant patterns, such a s Populus, Betula and Larix had greater total leaf area and root lengt h per unit plant mass (LAR and RLR, respectively) than the evergreens. Interspecific variation in RGR in both high and low light was positiv ely correlated (r approximate to 0.9) with SLA, SRL, LAR and RLR, and negatively correlated (r approximate to -0.9) to seed mass and leaf li fe span. 4. These data suggest that SLA, SRL, NAR and RGR are closely associated with variation in life-history traits and that variation in leaf and root structure more strongly influences patterns of RGR amon g species and light environments than does biomass partitioning.