Juniperusoccidentalis juvenile foliage: advantages and disadvantages for a stress-tolerant, invasive conifer

Abstract

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.

Difference in cuticular transpiration and sclerophylly in juvenile and adult pine needles relates to the species-specific rates of development

“…Yet, provenances from dry regions show a consistently longer juvenile phase (López et al 2007). This counter-intuitive outcome was also found in Juniperus occidentalis (Miller et al 1995). Juniperus occidentalis is a water stress-tolerant species that maintains the juvenile vegetative state as a strategy to enhance its competitive ability.…”

“…Intervals are standard errors. pna: P. pinea, bru: P. brutia, can : P. canariensis, rad: P. radiata; hal: P. halepensis, nig: P. nigra, ptr: P. pinaster, syl: P. sylvestris, unc: P. uncinata (Miller et al 1995;Darrow et al 2002). Our results support that the species from drier habitats tend to delay heteroblastic change, and this is generally related to lower cuticular transpiration of adult needles and higher differentiation between juvenile and adult foliage types (see correlations in Table 5).…”

“…Several conifer genera, such as Juniperus, Cupressus, Pinus and Cedrus show a marked heterophylly during their vegetative phase. It is still poorly known as to what extent this process is genetically fixed during ontogeny (Kubien et al 2007) or related to different adaptive strategies allowing them to cope with the contrasting environmental conditions they encounter (Miller et al 1995;Winn 1999).…”

“…Juniperus occidentalis is a water stress-tolerant species that maintains the juvenile vegetative state as a strategy to enhance its competitive ability. Although such strategy is thought to be a risky compromise, it allows more adaptive biomass allocation in the tree as the transition to the adult form occurs (Miller et al 1995;Climent et al 2006). If this is the case, we would expect that prolonged juvenility might be related to greater inter-specific variation in differentiation between juvenile and adult needles.…”

Freezing injury in primary and secondary needles of Mediterranean pine species of contrasting ecological niches

“…dles (Jimenez et al, 2000), which was confirmed in Juniperus occidentalis (Miller et al, 1995) but still not investigated in pines. However, while previous research have shown that secondary needles have a significantly lower cuticular transpiration than primary needles in this species (Climent et al, 2006), our experiment revealed similar susceptibility to frost injury which suggest different tolerance pathways between drought and cold.…”