Bud and growth-unit structure in seedlings and saplings of Nothofagus alpina (Nothofagaceae)

In temperate trees, axis length growth generally results from the differentiation of organs at the end of a growing season and the extension of such "preformed organs" in the next growing season. Neoformation, i.e., the simultaneous differentiation and extension of organs, has been studied for only a few species. Here we evaluated bud composition and growth unit (GU) size for seedlings and saplings of Nothofagus alpina, a valuable South American forest tree. Trunk GUs of seedlings and saplings included preformed and neoformed organs, whereas main-branch GUs of saplings were entirely preformed. The size of a GU was more closely related to the number of preformed green leaves than to the number of cataphylls of its preceding bud. Proximal buds of a trunk GU had more cataphylls and less green-leaf primordia than distal buds. Individual leaf area increased from proximal to distal positions on trunk GUs. For trunk and main-branch GUs, the length/width ratio was maximum for leaves in intermediate positions. The development of large neoformed leaves at the end of the growing season could increase the photosynthetic capacity of this species in late summer, when the activity of preformed organs is likely to be decreasing.     

Periods of organogenesis in shoots of Nothofagus dombeyi (Mirb.) oersted (Nothofagaceae)

The organogenetic cycle of main-branch shoots of Nothofagus dombeyi (Nothofagaceae) was studied. Twelve samples of 52-59 parent shoots were collected from a roadside population between September 1999 and October 2000. Variations over time in the number of nodes of terminal and axillary buds, and the length, diameter and number of leaves of shoots derived from these buds (sibling shoots) were analysed. The number of nodes of buds developed by parent shoots was compared with the number of nodes of buds developed, I year later, by sibling shoots. The length, diameter and number of leaves of sibling shoots increased from October 1999 to February 2000 in those shoots with a terminal bud. However, extension of most sibling shoots, including the first five most distal leaf primordia, ceased before February due to abscission of the shoot apex. Axillary buds located most distally on a shoot had more nodes than both terminal buds and more proximal axillary buds. The longest shoots included a preformed part and a neoformed part. The organogenetic event which initiated the neoformed organs continued until early autumn, giving rise to the following year's preformation. The absence of cataphylls in terminal buds could indicate a low intensity of shoot rest. The naked terminal bud of Nothofagus spp. could be interpreted as a structure less specialized than the scaled bud found in genera of Fagaceae and Betulaceae.     

Ontogeny of pistillate flowers and inflorescences in Nothofagus subgenus Lophozonia (Nothofagaceae)

  Cupule and pistillate inflorescence morphology is described in detail for the first time for a number of species in Nothofagus subgenus Lophozonia. The architecture and temporal appearance of prophylls, flowers, and cupule valves is dichasial; the cupule valves are third and higher order shoot systems. Comparative studies demonstrate that the dorsal rows of appendages on the cupule valves have a similar arrangement, and each row exhibits the same temporal pattern of development. This suggests that the cupule valves in all species have a modular construction and consist of rows of homologous appendages. This study clearly demonstrates the uniform groundplan of the pistillate inflorescence in this subgenus. Received March 14, 2002; accepted May 8, 2002 Published online: September 13, 2002     

Annual shoot-growth in Nothofagus antarctica (G. Forster) Oersted (Nothofagaceae) from northern Patagonia

The growth dynamics of annual shoots of Nothofagus antarctica shrubs from northern Patagonia was studied. The pattern of extension of the shoots derived from the three most distal buds of 100 parent shoots was registered. Weekly measurements and observations of extending shoots were carried out during the 1996–1997 growth season. The date of shoot extension initiation was less variable than the date of shoot extension cessation. Extension curves had an asymmetrically sigmoid outline. Most extension took place uninterruptedly between mid-September 1996 and the end of January 1997. Extension rate reached its highest value in the second half of the extension period. Leaf unfolding rate had a peak early in the extension period and fluctuated irregularly later on. The apical meristem of all shoots died by the end of shoot extension. In general terms, shoot length, diameter, leaf number and extension duration decreased from the first to the third position from the parent shoot’s apex, although exceptions to this pattern were found. Shoot extension rate was affected by maximum and minimum daily temperatures but not by the amount of precipitation during the extension period. The size of a bud was not related to the size of the shoot derived from it. The size of shoots in the third position from the apex was related to parent shoot size; this was not the case for more distal shoots. Received: 14 May 1999 / Accepted: 10 November 1999     

Out in the cold: genetic variation of Nothofagus pumilio (Nothofagaceae) provides evidence for latitudinally distinct evolutionary histories in austral South America

Nothofagus pumilio is the dominant and almost ubiquitous tree species in mountainous environments of temperate South America. We used two types of molecular markers (cpDNA and isozymes) to evaluate the effects of the Paleogene paleogeography of Patagonia and more recent climatic oscillations of the Neogene on such cold‐tolerant species’ genetic makeup. Phylogeographic analysis on sequences of three cpDNA non‐coding regions at 85 populations yielded two latitudinally disjunct monophyletic clades north and south of c. 42°S containing 11 and three haplotypes, respectively. This indicates a long‐lasting vicariant event due to the presence of an extended open paleobasin at mid latitudes of Patagonia. Also distribution patterns of cpDNA haplotypes suggest regional spread following stepping‐stone models using pre‐Cenozoic mountains as corridors. Comparable genetic diversity measured along 41 sampled populations using seven polymorphic isozyme loci provides evidence of local persistence and spread from multiple ice‐free locations. In addition, significantly higher heterozygosity and allelic richness at high latitudes, i.e. in areas of larger glacial extent, suggest survival in large and isolated refugia. While, higher cpDNA diversity in lower latitudes reflects the complex orogeny that historically isolated northern populations, lower isozyme diversity and reduced F_ST values provide evidence of local glacial survival in numerous small locales. Therefore, current genetic structure of N. pumilio is the result of regional processes which took place during the Tertiary that were enhanced by contemporary local effects of drift and isolation in response to Quaternary climatic cycles.     

Droplet-vitrification methods for apical bud cryopreservation of yacon [Smallanthus sonchifolius (Poepp. and Endl.) H. Rob.]

This study aimed to develop a cryopreservation protocol for the long-term preservation of yacon [Smallanthus sonchifolius (Poepp. and Endl.)], an Andean crop with high fructooligosaccharide content in its tuberous roots. Initially, the cryopreservation protocol was developed using a yacon clone originated from Ecuador classified as ECU 41. Osmotic dehydration of apical buds (2–3 mm long) was carried out by assessing two plant vitrification solutions, PVS2 (15, 30, and 60 min) at 0 °C and PVS3 (30, 45, 60, and 75 min) at 22 °C. After cryopreservation, the apical buds were thawed and placed on MS medium?±?0.1 mg l^?1 N⁶-benzyladenine (BA). The survival rates ranged from 37 to 90% within all treatments, with those subjected to PVS2 and PVS3 for 60 min showing the highest survival rates on MS medium without BA (87 and 90%, respectively). At 12 weeks post cryopreservation, these treatments also provided the highest regrowth rates, both reaching 73% of normally growing (shooting, rooting) plantlets. Survival rates on MS?+?0.1 mg l^?1 BA regrowth medium reached up to 90%; however, regrowth into normally rooted plantlets did not exceed 67% post cryopreservation. The optimized protocols were then applied to 4 additional yacon clones originated from Bolivia and Peru, classified as BOL 22, BOL 23, PER 12, and PER 14. This resulted in survival and regeneration rates ranging between 79.7–94.1% and 66.3–75.4% respectively. Our study shows that optimal cryopreservation protocols for the long-term conservation of yacon can be based on both PVS2 and PVS3 vitrification solutions.

     

Shoot regeneration and somatic embryogenesis from needles of redwood (Sequoia sempervirens (D.Don.) Endl.)

A rapid and effective system of somatic embryogenesis and organogenesis from the in vitro needles of redwood (Sequoia sempervirens (D.Don.) Endl.) had been established. The influences of plant growth regulators (PGRs) and days of seedlings in vitro on adventitious bud regeneration and somatic embryogenesis were studied. The process of somatic embryo formation was also observed. The results showed that embryogenic callus was induced and proliferated on Schenk and Hildebrandt (SH) medium with BA (0.5 mg/l), KT (0.5 mg/l) and IBA (1.0 mg/l). SH medium containing BA (0.5 mg/l), KT (0.2 mg/l) and IBA (0.2 mg/l) effectively promoted adventitious bud regeneration. The highest frequency (66.3%) of direct somatic embryogenesis was obtained in the combination of BA (0.5 mg/l) and IBA (0.5 mg/l). The optimal days of seedling in vitro for adventitious bud and somatic embryogenesis were 30 days and 30–40 days, respectively. The developments of somatic embryos were similar to that of zygotic embryogenesis. The result of histocytological studies indicated that proteins were gradually accumulated in the process of somatic embryo formation and there were two peaks of starch grains accumulation that one was in the embryogenic callus and the other was in the globular embryos. These results indicated that starch and protein were closely related with the energy supply and the molecular base of somatic embryogenesis, respectively.     

Preformation and neoformation in shoots of Nothofagus antarctica (G. Forster) Oerst. (Nothofagaceae) shrubs from northern Patagonia

The size (length and diameter) and number of leaf primordia of winter buds of Nothofagus antarctica (G. Forster) Oerst. shrubs were compared with the size and number of leaves of shoots derived from buds in equivalent positions. Buds developed in two successive years were compared in terms of size and number of leaf primordia. Bud size and the number of leaf primordia per bud were greater for distal than for proximally positioned buds. Shoots that developed in the five positions closest to the distal end of their parent shoots had significantly more leaves than more proximally positioned shoots of the same parent shoots. The positive relationship between the size of a shoot and that of its parent shoot was stronger for proximal than for distal positions on the parent shoots. For each bud position on the parent shoots there were differences in the number of leaf primordia per bud between consecutive years. The correlations between the number of leaf primordia per bud and bud size, bud position and parent shoot size varied between years. Only shoots produced close to the distal end of a parent shoot developed neoformed leaves; more proximal sibling shoots consisted entirely of preformed leaves. Leaf neoformation, a process usually linked with high shoot vigour in woody plants, seems to be widespread among the relatively small shoots developed in N. antarctica shrubs, which may relate to the species' opportunistic response to disturbance.     

Leaf architecture of South American Nothofagus (Nothofagaceae) using traditional and new methods in morphometrics

Leaf morphology has been the subject of several studies in NoNothofagur especially in the context of the taxonomy and evolutionary relationships of taxa within the genus, which are still controversial. The leaf architecture of 8 dombgi , N. betuloides and N. nitida , dominant trees of temperate forest in southern South America, is compared using venation patterns, landmarks, and entire outlines. In terms of venation patterns N. dombgi and N. betuloides were more similar to each other than to N. nitida. Similar results were found when differences in shape were analysed by discriminant analyses of shape coordinates (landmarks) and Fourier coefficients (outlines). For both analyses, the fwst discriminant function separated N. nitida from the other two species; these were also distinguished but showed greater overlap with each other. This study, in concert with information from allozyme data confirms the hypothesis of a more ancestral position for N. nitida with N. dombgi and N. betuloides being more recently derived. In addition to differences in shape, the size component of leaf morphology indicated that whereas N. betuloides had the smallest leaves, N. dombgi spanned the greatest range and has the biggest leaves. Given that the data shown here were obtained from seedlings grown under common-garden conditions, differences in both shape and size, seem to be important components of leaf morphology that may warrant consideration in characterizing these and other species of Nothofagus.     

Preformation and distribution of staminate and pistillate flowers in growth units of Nothofagus alpina and N. obliqua (Nothofagaceae)

Background and Aims

The distribution and differentiation times of flowers in monoecious wind-pollinated plants are fundamental for the understanding of their mating patterns and evolution. Two closely related South American Nothofagus species were compared with regard to the differentiation times and positions of staminate and pistillate flowers along their parent growth units (GUs) by quantitative means.

Methods

Two samples of GUs that had extended in the 2004–2005 growing season were taken in 2005 and 2006 from trees in the Lanín National Park, Patagonia, Argentina. For the first sample, axillary buds of the parent GUs were dissected and the leaf, bud and flower primordia of these buds were identified. The second sample included all branches derived from the parent GUs in the 2005–2006 growing season.

Key Results

Both species developed flowering GUs with staminate and/or pistillate flowers; GUs with both flower types were the most common. The position of staminate flowers along GUs was similar between species and close to the proximal end of the GUs. Pistillate flowers were developed more distally along the GUs in N. alpina than in N. obliqua. In N. alpina, the nodes bearing staminate and pistillate flowers were separated by one to several nodes with axillary buds, something not observed in N. obliqua. Markovian models supported this between-species difference. Flowering GUs, including all of their leaves and flowers were entirely preformed in the winter buds.

Conclusions

Staminate and pistillate flowers of N. alpina and N. obliqua are differentiated at precise locations on GUs in the growing season preceding that of their antheses. The differences between N. alpina and N. obliqua (and other South American Nothofagus species) regarding flower distribution might relate to the time of anthesis of each flower type and, in turn, to the probabilities of self-pollination at the GU level.Key words: Branch, bud, growth unit, Markovian models, Nothofagus alpina, N. obliqua, Patagonian forests, pistillate flower, preformation, staminate flower     

Organogenesis in vitro of Nothofagus alpina (P. et E.) Oerst, Fagaceae

In vitro shoot and root regeneration of 2-year-old Nothofagus alpina plants was achieved from several types of expiants cultured in vitro on a modified Woody Plant Medium formulation. Multiple shoot formation was obtained from leaf expiants using 0.45–2.27 M thidiazuron and 0.0049–0.098 M indolebutyric acid. Excised axillary buds formed shoots and roots in the presence of 0.0049 M benzyladenine and 2.46 M indolebutyric acid, or in the absence of plant growth regulators. Nodal sections rooted when 2.46 M indolebutyric acid at was supplied in the medium. Subcultured shoots originating from nodal sections showed a high regeneration rate through multiple shoot and root formation.Abbreviations BA benzyladenine - GA₃ giberellic acid - IBA indolebutyric acid - NAA -naphthaleneacetic acid - TDZ thidiazuron - WPM McCown's Woody Plant Medium - Z zeatin     

Intraspecific trait variation and covariation in a widespread tree species (Nothofagus pumilio) in southern Chile

? The focus of the trait-based approach to study community ecology has mostly been on trait comparisons at the interspecific level. Here we quantified intraspecific variation and covariation of leaf mass per area (LMA) and wood density (WD) in monospecific forests of the widespread tree species Nothofagus pumilio to determine its magnitude and whether it is related to environmental conditions and ontogeny. We also discuss probable mechanisms controlling the trait variation found. ? We collected leaf and stem woody tissues from 30-50 trees of different ages (ontogeny) from each of four populations at differing elevations (i.e. temperatures) and placed at each of three locations differing in soil moisture. ? The total variation in LMA (coefficient of variation (CV) = 21.14%) was twice that of WD (CV = 10.52%). The total variation in traits was never less than 23% when compared with interspecific studies. Differences in elevation (temperature) for the most part explained variation in LMA, while differences in soil moisture and ontogeny explained the variation in WD. Traits covaried similarly in the altitudinal gradient only. ? Functional traits of N. pumilio exhibited nonnegligible variation; LMA varied for the most part with temperature, while WD mostly varied with moisture and ontogeny. We demonstrate that environmental variation can cause important trait variation without species turnover.     

Growth-unit structure in trees: effects of branch category and position on Nothofagus nervosa, N. obliqua and their hybrids (Nothofagaceae)

In plants with rhythmic growth, a branch segment extended in one event is known as growth unit (GU). GU structure, resulting from the resources allocated to stem length, volume and mass, and to leaf area and mass, is relevant for understanding branch functioning in the context of plant development. This study compares GU structure between main branches and short branches positioned at low and high positions on nursery-grown trees of three closely related genetic entities: Nothofagus nervosa, N. obliqua and natural hybrids between these species. GUs of short branches, compared to those of main branches, had lower length, diameter and number of leaves, and higher specific leaf area (SLA), stem density and proportional mass in leaves than in stems. GUs at high position on the trees had a higher proportion of their mass in stem than in leaves and a lower SLA than those at low position. Stem density was higher for N. nervosa and the hybrid trees than for N. obliqua. Most other GU traits did not differ statistically between the considered genetic entities. The three genetic entities exhibited distinct patterns of variation in leaf size with leaf position along main-branch GUs. The individual tree had a significant effect on most variables. GU structure would have a major ontogenetic component and would play a relevant role in the architecture of Nothofagus species and their adaptation to different environmental conditions.     

Structural Organization of the Shoot Apex and Axillary Bud in Slipper Spurge (Pedilanthus tithymaloides Poit.) I

The slipper spurge (Pedilanthus tithymaloides) is a small cactus-likeherbaceous plant. The shoot apex has a single tunica layer andsometimes the second layer also simulates it. There is a centralmeristem zone whose significance could not be determined. Thefirst bud meristem differentiates at the second node. The earliestbud meristem has a procambium but no shell zone was observed.The node is trilacunar. There are three bud traces and threeprophyll traces. The single prophyll is situated at right anglesto the subtending leaf.     

Natural hybridization between a deciduous (Nothofagus antarctica, Nothofagaceae) and an evergreen (N. dombeyi) forest tree species: evidence from morphological and isoenzymatic traits

BACKGROUND AND AIMS: Trees with a partial leaf-shedding pattern and other morphological features a priori considered intermediate between those of the deciduous Nothofagus antarctica (G. Forster) Oersted and the evergreen N. dombeyi (Mirb.) Oersted (Nothofagaceae) were found in natural stands. The hybridization between a deciduous and an evergreen species of Nothofagus has not been reported so far in natural communities. METHODS: The putative hybrids and the two presumed parental species were compared using 14 enzyme systems as well as shoot, leaf and reproductive morphology. KEY RESULTS: Six enzyme systems showed good resolution (MDH-B, IDH, SKDH, 6-PGDH, GOT and PGI) and in four of them (PGI, MDH-B, SKDH and 6-PGDH) the putative hybrids showed intermediate zymogram patterns between N. antarctica and N. dombeyi. Both principal coordinates analysis on isozyme data and principal components analysis (PCA) on quantitative morphological traits of shoots and leaves separated both parental species and located the putative hybrids closer to N. antarctica than to N. dombeyi. In the PCA, the number of basal cataphylls and the length : width ratio of leaves were the variables most discriminating among shoots of the three entities. The putative hybrids were intermediate between both species regarding leaf vernation, outline and venation, variation in leaf shape (length/width) with position on the parent shoot and in staminate inflorescence and cupule morphology. For other morphological traits, the putative hybrids resembled one of the parental species or differed from both species (e.g. valve morphology). CONCLUSIONS: Isoenzymatic and morphological data sets support the idea of the hybrid nature (probably F1 generation) of the semi-deciduous trees found. Nothofagus antarctica and N. dombeyi are probably more closely related than previously assumed. The relevance of pollen type in revealing evolutionary relationships between Nothofagus species is supported, and that of leaf-shedding pattern is rejected.     

Variations in Seed Size Within Populations of Silene dioica (L.) Clairv. in Relation to Habitat

The sizes of seeds in populations of Silene dioica were comparedincluding observations on variation within and between plantsin a population growing wild in south-east England. The meanseed weights of different populations from Europe displayedvariations, which contrasted with rather stable means foundin a population sampled in 4 different years, or compared whengrowing under natural conditions or in cultivation. Variationsfrom plant to plant within a population, between populationswithin a particular area, and between different capsules fromthe same plant were similar in range and distribution to thedifferences found between populations. Seed size did not appearto be correlated with season of maturity, level of dormancy,or position on the flower truss, but significant differenceswere found in mean seed weights from different individual plants. The results are discussed in relation to the natural distributionof the species, and its role as an opportunist species inhabitingthe edges of deciduous woodlands. Silene dioica (L.) Clairv., red campion, seed size     

Cytology of two species of winged bean, Psophocarpus tetragonolobus (L.) DC. and P. scandens (Endl.) Verde. (Leguminosae)

Karyotype morphology of Psophocarpus tetragonolobus and P. scandens is described and the behaviour of chromosomes at meiosis discussed. Both species have a chromosome number of 2n = 18 and similar karyotypes of a sort unusual within the Phaseolinae. Differences between the species in detailed morphology of the chromosomes agree with data from external morphology, palynology and crossability in indicating that P. scandens cannot be the immediate wild ancestor of domesticated P. tetragonolobus . Study of meiotic chromosomes and analysis of qualitative and quantitative variation in Papua New Guinean P. tetragonolobus suggest that there are few restrictions to recombination other than those imposed by predominant self-pollination, The bearing of these data on the taxonomic relationships of Psophocarpus and on chromosomal evolution within the Phaseolinae is discussed.     

Regional tectonics, disturbance, and population size of isolated stands of Nothofagus fusca (Nothofagaceae) in a forest ecotone in south-western New Zealand

Aim New Zealand's cool temperate forests are usually dominated by one or more of the five native taxa of Nothofagus (Nothofagaceae; southern beech), but in certain regions there are sharp boundaries against podocarp–broadleaved forest where Nothofagus is rare or completely absent, either for historical (Pleistocene Glaciation) or climatic/biological (mild superhumid climate and competition) reasons. The dynamics of a Nothofagus boundary was investigated by monitoring disturbance-initiated establishment of isolated stands of N. fusca at the extreme limits of its regional distribution. Location The research was carried out in a regional forest ecotone between Nothofagus forest and podocarp–broadleaved forest in the upper Taramakau Valley, South Island, New Zealand. The survey region straddles a major, active fault system and associated tectonic movements and earthquakes with more distant epicentres have contributed to intermittent canopy disturbance of the local forests. Methods Isolated stands of Nothofagus fusca beyond the limits of continuous Nothofagus forest were investigated during two field surveys, separated by 7–10 years. Changes in population size, stem diameter of individual trees, stand basal area and mean annual diameter increment were calculated for each of fifty-four isolated stands. Types of past and recent disturbance and the probable cause of mortality of trees were noted. Results The total population of fifty-four sample stands, ranging in size from one to > 400 stems, increased by 37.4%, and compound basal area increased by 4.7% between the two surveys. Mean stem diameter growth of isolated stands was lower than expected by empirical data for N. fusca, suggesting reduced wood increment at the limits of its distribution. Tree mortality was 0.8% per year. Fifty-one per cent of the dead stems had died as a consequence of various types of natural disturbance, uproots being more common than snaps and crown breakage. Main conclusions The isolated N. fusca stands preferentially occupy sites likely to experience intermittent disturbance, mostly including disturbance of the soil cover, which facilitates their initial establishment and persistence. Because of causal relationships between mass movement on steep slopes and erosion/deposition of talus fans and river terraces, disturbance-initiated changes in forest composition are observed across a range of different landforms.