Physiological processes for juvenile and adult foliage of Juniperusoccidentalis Hook. were compared to evaluate the advantages and disadvantages of juvenile foliage for a stress-tolerant, invasive conifer. Above- and below-ground biomass allocation and monthly measurements (April through October) of gas exchange, water relations, foliar nitrogen concentrations, and growth were made for juvenile and small-adult trees in the field in central Oregon. Compared with small adults, juveniles have greater allocations to foliage and fine-root biomass, higher rates of CO2 assimilation, leaf conductance, and transpiration, and lower investments of biomass and nitrogen per unit of foliar area. Juvenile foliage is less costly to produce than adult foliage. The suite of physiological processes associated with juvenile awl-like foliage should enhance establishment and early growth of J. occidentalis. However, high rates of water loss, which are associated with high rates of CO2 assimilation of juvenile foliage, appear to be a liability for large trees in the semiarid environment of eastern Oregon. Once established, the transition to a more conservative use of resources associated with adult scale-like foliage is consistent with the stress-tolerant strategy of long-lived evergreen trees.
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Seeds of greasewood (Surcobotus vermiculatus (Hook.) Torr.) were germinated at 50 to 400 C in 5-degree increments to determine temperature response. Seeds were also germinated in solutions of polyethylene glycol 6,000 (PEG), NaCI, and NarSO4, each at osmotic potentials of 0 to -4.2 MPa in -0.3 MPa decrements at 10, 20 and 30" C to determine moisture stress, specific ion, and temperature interaction. Germination was high at all temperatures, 5' C through 25" C being optimal. A direct linear relationship existed between total germination and osmotic potential of each solution at each temperature. Mean germhration at 30" C was significantly different for each osmotica with NaCl highest and PEG lowest. Mean germination at 10" C and 20" was not different within osmotica; however, total germination was significantly lower in PEG than in NaCl and NaeS04, indicating the difference between macromolecular PEG and ions (Na', Cl-and Sod=). Significant difference was observed in the coefficient of rate of germination between ions of Cl-and SOa=, with SO4 = being more stressful.
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