Abstract
Although the variations in within-crown cone production have mainly been associated with resource availability, trees with relatively fewer cones allocate more cones to the optimal vertical layer for cone production than their expected resource availability suggests. We investigated the number of cones (NCone) per branch basal area (BBA) and the proportion of cones (PCone) in the three crown layers (upper, middle, and lower) for 72 Pinus densiflora Sieb. et Zucc. clones in 2004 and 2005. We also measured cone characteristics in each layer to infer their resource or pollen availability. Further, in 2006 we conducted pollination experiments for another 19 P. densiflora ramets, manipulating pollen quality (open-pollinated, self-pollinated (selfed), and polycrossed) in their two crown layers (upper and lower), and examined how pollen quality could affect the among-layer differences. Among 72 clones investigated, PCone in the upper crown layer was significantly greater, with a decrease of the total NCone per BBA; at that time, the seed/ovule ratio (S/O) in the upper crown layer cones was generally greater than that found in the middle and lower crown layers. In the pollination experiments, self-pollination resulted in a decreased S/O in the cones, regardless of the crown layer: S/O in the selfed cones, which were pollinated with controlled-quality pollen, did not differ between the upper and lower layers. Clones with relatively fewer cones allocated more resources to producing cones in the optimal cone-producing layer (upper crown layer) than would be expected from their biomass allocation, suggesting that optimal cone production is the result of a pollination-related factor.
Published Version
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