Physiological ecology of western juniper (Juniperus occidentalis hook. subsp. occidentalis)

Graduation date: 1990Patterns and costs of root/shoot allocations, response to reductions of above and below-ground tissue and to fertilization with nitrate and ammonium, and seasonal courses of physiological processes were measured on juvenile, small-adult, and large-adult Juniperus occidentalis growing in the field under ambient\ud environmental conditions in eastern Oregon.\ud Adult foliage had the highest heat of combustion,\ud nitrogen concentrations, and construction cost. Allocation\ud patterns indicated a larger investment in resources to above\ud than below-ground tissue.\ud J. occidentalis allocated larger proportions of dry\ud mass to foliage, to maximize photosynthetic capacity, and to\ud roots, to optimize water and nutrient acquisition; this was accomplished through reduction of allocation to branches and\ud trunk.\ud Removing [approximately] 50% of the foliage increased rates of CO₂\ud assimilation but did not increase growth, improve water\ud status, or increase nitrogen concentration of remaining\ud foliage. Cutting lateral roots reduced physiological\ud processes and quantum-use-efficiencies and water-use-efficiencies.\ud Fertilization increased foliar nitrogen concentrations\ud and reduced CO₂ assimilation, leaf conductance, and\ud transpiration. Juniperus occidentalis appears to be adapted\ud to the low, ambient levels of soil nitrate and does not\ud preferentially utilize ammonium.\ud Highest daily total assimilation occurred during July\ud and August. Juveniles had significantly higher assimilation\ud and transpiration per gram foliage than did small or large-adults.\ud Juveniles had the tightest control over water\ud loss, but were not more water-use-efficient than small-adults\ud or large-adults. Soil drought affected conductance\ud independent of plant water potentials or vapor pressure\ud deficits. Branchlet elongation was greatest in June and\ud July. Juveniles were more responsive to the changing\ud environment that were small-adults or large adults