- Smith, Ronald Frank
The Graduate School, University of Maine
Field and greenhouse trials were established to determine the effects of stem injections of gibberellins A4 and A7 (GA) not eh numbers of and within-crown distribution of seed- and pollen-cones in black spruce (Picea mariana (Mill.) B.S.P.). In jetting GA increased the proportions of buds above the injection-point that developed reproductively. Combining GA with root pruning (RP) produced a greater increase in reproductive bud production than either treatment alone, but the complementary effect was less during the warm, dry summer in 1991 than during the wet summer in 1992. In the greenhouse, drought or root pruning were required for GA to induce cones.
The third objective of this study was to determine the effects of cone-induction treatments on current-year needle morphology, photosynthetic capacity, and gas-exchange properties. Drought increased pre-dawn shoot water potential (PMS), during the period that irrigation was withheld, but had no persistent effect on current-year needle development or rates of gas exchange. conversely, RP did not affect PMS but significantly reduced current-year needle growth, nitrogen and chlorophyll contents, and rates of gas exchange. The potential implications of these results for cone development are discussed.