Temperate Woody Species Research Articles

Execution of the auxin replacement apical dominance experiment in temperate woody species

The classic Thimann-Skoog or auxin replacement apical dominance test of exogenous auxin repression of lateral bud outgrowth was successfully executed in both seedlings and older trees of white ash, green ash, and red oak under the following conditions: (1) decapitation of a twig apex and auxin replacement were carried out during spring flush, (2) the decapitation was in the previous season's overwintered wood, and (3) the point of decapitation was below the upper large irrepressible lateral buds but above the lower repressible lateral buds. Although it has been suggested that neither auxin, the terminal bud, nor apical dominance have control over the outgrowth of the irrepressible buds during spring flush, there is evidence in the present study that indicates that such control over the repressible buds exists. In seedlings, second-order branching, which resulted from decapitation of elongating current shoots, was also inhibited by exogenous auxin in the three species. Hence, the auxin replacement experiments did work on year-old proleptic buds (of branches of older trees) that would have entered the bud bank and also on current buds of seedlings. Cytokinin treatments were ineffectual in promoting bud growth.

The Role of Apical Dominance in Paradormancy of Temperate Woody Plants: A Reappraisal

Paradormancy, also known as summer dormancy, is the temporary dormancy which precedes winter or endodormancy in temperate woody plants. Apical dominance, the control exerted by the shoot apex over the outgrowth of the lateral buds, is thought to play a primary role in the paradormancy of these current lateral buds which normally do not grow out until the following spring after over-wintering. In the present study, to test apical dominance, periodic decapitation and defoliation beginning with early spring flushing and extending through the growing season were carried out on eleven tree species (white ash, green ash, red oak, black walnut, pignut hickory, shagbark hickory, sweetgum, cottonwood, sugar maple, hybrid silver/red maple and white pine) ranging in age from 6 to 50–60 years. Significant decapitation and defoliation release of current lateral buds into growing branches was found only in silver/red hybrid maple and red oak, respectively. In a greenhouse study of 1-year-old sugar maple and green ash seedlings, a significant response was found only in the latter. The lack of response in most of the older species analyzed indicates that other inhibitory influences may be overriding that of apical dominance and suggests that apical dominance does not play the primary role in paradormancy in some temperate woody species.

Expression of beta‐tubulin during dormancy induction and release in apical and axillary buds of five woody species

Cell cycle activity was studied in apical and axillary buds of Norway maple (Acer platanoides L.), apple (Malus‘M9’), pedunculate oak (Quercus robur L.), Scots pine (Pinus sylvestris L.) and rose (Rosa corymbifera‘Laxa’) during dormancy induction and release. Flow cytometric analyses revealed that in dormant buds, cells mainly were quiescent at the G0/G1 phase, while in non‐dormant buds, a significantly higher frequency of G2 cells was found in all species. In western blots accumulation of 55 kDa beta‐tubulin was found in active growing plant material, whereas in dormant buds the accumulation was much lower or below detection level. It was observed for all species that during dormancy induction the amount of beta‐tubulin decreased, while during dormancy release a fast accumulation of beta‐tubulin occurred. The dynamics of the beta‐tubulin accumulation reflected the dormancy status of tree buds of the five species studied suggesting that the beta‐tubulin level might be useful as a marker for the dormancy status in buds of temperate woody species.

Stoichiometry of foliar carbon constituents varies along light gradients in temperate woody canopies: implications for foliage morphological plasticity.

Foliar morphology and chemical composition were examined along a light gradient in the canopies of five deciduous temperate woody species, ranked according to shade-tolerance as Populus tremula L. < Fraxinus excelsior L. < Tilia cordata Mill. = Corylus avellana L. < Fagus sylvatica L. Foliar carbon was divided between structural (cell-wall polysaccharides, lignin) and nonstructural (proteins, ethanol-soluble carbohydrates, starch) fractions. Foliar morphology of all species was strongly affected by irradiance. Both leaf dry mass per area (M(A)), a product of leaf density and thickness, and leaf dry to fresh mass ratio (D(w)), characterizing the apoplastic leaf fraction, increased with increasing relative irradiance (I(sum), calculated as the weighted mean of fractional penetration of diffuse and direct irradiance). Though the relationships were qualitatively identical among the taxa, more shade-tolerant species generally had lower values of M(A) than shade-intolerant species, and their morphological relationships with irradiance were curvilinear; however, there were no signs of saturation even at the highest irradiances in shade-intolerant species. In all species, lignin concentrations increased and cell-wall polysaccharide concentrations decreased with increasing irradiance. Consequently, biomass investment in structural leaf components appeared to be relatively constant along light gradients. The relationship between irradiance and structural compounds tended to be asymptotic in the more shade-tolerant species, whereas M(A) was linearly correlated with concentrations of structural leaf components, suggesting that similar factors were responsible for the curvature in the morphological and chemical relationships with irradiance. Because lignin increases tissue elastic modulus thereby rendering leaves more resistant to low leaf water potentials, we conclude that changes in stoichiometry of cell wall components were related to foliage acclimation to the gradients of water deficit that develop in the canopy and inherently accompany light gradients. We also conclude that increased lignification decreased leaf expansion growth, and that species differences in lignification were partly responsible for the observed interspecific variability in morphological plasticity. Analysis of structural leaf compounds provided no indication of how shade-intolerant species with low investments in lignin acclimated to gradients of water availability in the canopy. Because shade-intolerant species generally had higher capacities for photosynthesis than shade-tolerant species, we postulated that they should also have a greater ability for osmotic adjustment of leaf water potential with photosynthates. The concentrations of soluble carbohydrates increased with increasing irradiance in all species; however, the osmotic adjustment achieved in this way was similar in all species, except for shade-intolerant F. excelsior, which had a lower potential for osmotic adjustment with carbohydrates than the other taxa. Although we did not determine whether the gradients of stem water potential and leaf water deficits were similar in canopies of different species, we demonstrated that water relations play a central role in determining foliar structure and composition along light gradients in the canopy.

Rehydration effects on pressure-volume relationships in four temperate woody species: variability with site, time of season and drought conditions.

Seasonal pressure-volume (P-V) analyses were conducted on rehydrated and non-rehydrated leaves of Quercus rubra, Q. ilicifolia, Q. prinus, and Fraxinus americana in central Pennsylvania, U.S.A., to test the hypothesis that rehydration-induced shifts in P-V parameters occur in woody species from a non-arid region, and that the magnitude of these shifts increases with species drought tolerance and drought conditions. The species from a xeric ridge (Q. ilicifolia and Q. prinus) displayed increases of about 0.4-0.6 MPa in the osmotic potentials at full and zero turgor and a concurrent loss of symplastic solutes following 12 h and 24 h rehydration, particularly during a late-season drought. In contrast, the mesic, valley species (Q. rubra and F. americana) did not display significant shifts in osmotic parameters with rehydration at any time. In several instances, the relative water content at zero turgor (RWC0) increased by about 6% (e.g., from 85% to 91%) and the bulk elastic modulus (ε) decreased by about 4.0 MPa following rehydration and correction for the plateau effect; the magnitude of these shifts was greatest in the xeric species. However, when data were not corrected for the plateau effect, RWC0 decreased by about 4% in some of the species/date combinations. Plateaus were also responsible for some of the decrease in ε with rehydration, but not for the shifts in osmotic potentials. The largest increases in osmotic potentials corresponded with decreases in tissue osmotic solute content. Rehydration-induced shifts in P-V parameters were responsible for masking or reducing most of the species and seasonal differences exhibited in nonrehydrated samples.

Plant tissue culture: Perceptions and realities

There is a perception that phenomenal progress has been made in so-called tissue culture technologies as they apply to non-woody plants. Moreover, many also seem to think that while temperate woody species have yielded toin vitro manipulation, tropical and subtropical ones have generally remained recalcitrant. An attempt has been made to place all this in context, and to allow for emergence of a realistic conclusion of where we really seem to be. Much progress has been made but plant tissue culture procedures still have a long way to go before they can collectively qualify, by the most rigid criteria, as a routine tool. If a technology is, in fact, a means to amplify our ability to do something in a relatively, if not virtually, risk-free manner, anyone who has done much serious plant tissue culture will know that in most cases it does not yet meet the criterion. When we can predictably control things—with maximal certainty, risk-free, or at least with minimal or acceptable risk, we will have a biotechnology. It sounds very modern to use the word ‘biotechnology’ but one does not achieve the status of a biotechnology merely by many or most agreeing to use the term. My belief is that we work against ourselves by doing so. Basic scientific inquiry is stifled. We still need to provide an appropriate framework and vehicle for basic investigations that will enable many important unanswered questions to be addressed. From a practical perspective these include: Why does progress seem to be slow in woody plants—especially in the case of tropical and subtropical species; what are some of the constraints imposed on the systems being worked with; how much of a gap is there between knowledge at the research level and application; how can one accelerate activities to improve both our perspective and still make positive basic and practical contributions to this area? A major problem has been that some systems are quite for along in their development; others are in their infancy. It is hoped that supporters of plant tissue culture efforts will not abandon basic research programs in favor of applied initiatives just because some species seem to be more difficult to work with initially than others and hence will require much more time at the basic research level, and well before one can begin to develop and ultimately exploit. Basic botanical and plant cell biology research must be fostered. Those dedicated to studying plant biology from anin vitro perspective have a greater role now than ever to play. Responsible action is crucial. Resistance must be given to those who prematurely insist that integration into practical schemes should predominate our thinking and setting of priorities. At the same time there is a delicate path that must be taken so that opportunities for learning and making basic contributions are not missed. Plant scientists clearly have a challenge to meet. Decision making must take into account the state of the science from the scientists’ perspective—not merely an administrative perspective.

Field water relations of three temperate vines.

A two year comparative field water relations study was conducted in central Maryland on three sympatric temperate lianas, Lonicera japonica, Vitis vulpina and Parthenocissus quinquefolia. Seasonal physiological activity was longer by approximately 9 weeks in the evergreen L. japonica, while peak rates of stem elongation were 4-10 fold higher in the two deciduous species. There were marked differences in vascular anatomy and water use patterns among the three species, however all three evidenced varying degrees of stomatal closure in response to decreasing soil water availability and increasing atmospheric evaporative demand. The range of leaf water potentials measured in these species was quite narrow in comparison to other temperate woody species. Two of the species showed no alterations in their tissue water release properties in response to decreased soil water availability, while V. vulpina showed a limited capacity in this regard. Most significant among the species differences in water relations were the conservative water use patterns of P. quinquefolia, and the midday maxima of transpirational water loss measured in L. japonica compared to the morning peaks in traspiration for the two deciduous species. The differences found in anatomy, leaf phenology, climbing mechanics, water relations and canopy development among these three sympatric vines implies a spatial and temporal partitioning of light and water resources and emphasizes the diversity of morphological-physiological suites of characters present among species co-occurring in the same macrohabitat.

Temperate Woody Species as Interior Landscape Plants

The feasibility of employing temperate woody species in the interior landscape was examined. The indoor performance of deciduous and evergreen plants was observed. Selected species of Taxus, Caragana, Cornus, Ilex, Acer and Euonymus showed potential for indoor use. Condition of plants at the time of introduction to the interior environment was investigated, including adjustment to light level of the plants before indoor placement. Installation of dormant plants was more successful than the installation of actively growing material.