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.     

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     

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.     

Axis differentiation in two South American Nothofagus species (Nothofagaceae)

An analysis was carried out on the length, diameter and number of leaves, and the ratios between these variables for current-year growth units (sibling growth units) derived from different nodes of previous-year growth units (parent growth units) of young Nothofagus dombeyi and Nothofagus pumilio trees. Changes in sibling growth unit length, diameter, and number of leaves with position on the parent growth unit were assessed. In both species, sibling-growth unit morphology varied according to both the axis type of the parent growth unit and the position of the sibling growth unit on its parent growth unit. For the largest parent growth units, the length, diameter and number of leaves of their sibling growth units decreased from distal to proximal positions on the parent growth unit. Distal sibling growth units had a more slender stem and longer internodes than proximal sibling growth units. Sibling growth units in equivalent positions tended to have a more slender stem for N. dombeyi than for N. pumilio. Long main-branch growth units of N. pumilio had longer internodes than those of N. dombeyi; the converse was true for shorter growth units. The growth unit diameter/leaf number ratio was consistently higher for N. pumilio than for N. dombeyi. Nothofagus pumilio axes would go through a faster transition from an 'exploring' morphology to an 'exploiting' morphology than N. dombeyi axes. Within- and between-species variations in growth unit morphology should be considered when assessing the adaptive value of the branching pattern of plants.     

The hydraulic architecture of balsam fir (Abies balsamea)

Leaf-specific conductivities (LSCs – hydraulic conductivity per dry weight of supplied leaves). Huber values (transverse sapwood area per dry weight of supplied leaves), specific conductivity (hydraulic conductivity per transverse sapwood area) and tracheid diameters were measured throughout the trunk and crown of 20-year-old trees of Abies balsamca (L.) Mill. Measured specific conductivity was proportional to the radius to the fourth power of tracheids. LSCs, which indicate the relative water availability to different plant parts, are much higher in the trunk than in first order branches, and lowest in second order branches. The structural basis for this "hydraulic hierarchy" lies both in Huber values and in tracheid diameters. For similar diameter stem segments, there was no statistically significant difference for trunks versus branches in specific conductivity. However, in old parts of the tree, trunks are wider than supported branches and producer wider tracheids resulting in greater specific conductivities than in branches. In vigorous trees with strong apical control, Huber values were 12.0 times greater in the trunk than in similar diameter branch segments. In slow-growing trees with weak apical control, Huber values were 2.2 times greater in the trunk versus similar branch segments.     

Is the Vertical Transmission of Neotyphodium lolii in Perennial Ryegrass the Only Possible Way to the Spread of Endophytes?

Endophytic fungi live their whole life within host tissues usually without any visible symptoms. Their vertical transmission (seed-plant-seed) has been well described and documented. However, horizontal transmission (plant-plant) needs more clarification. The aim of this study was to assess the extent to which endophytes move vertically in ecotypes of perennial ryegrass and whether there is evidence for the horizontal transmission of endophytes. Ecotypes from grasslands in Poland were collected in the form of living plants and used for vertical transmission analysis. Plants, the seed collected from these plants and plants grown from this collected seed were tested for endophytic infection. Provided that all produced seeds were viable and able to germinate and produce seedlings, the vertical transmission of Neotyphodium endophytes in perennial ryegrass ecotypes was nearly complete. For the horizontal transmission experiment, endophyte-hosting plants (E+) and endophyte-free plants (E-) of four cultivars were planted in the field in close proximity on small plots that were frequently mown. These studies revealed that after 7 months of growth next to E+ plants, the characteristic Neotyphodium spp. mycelia were found in E- plants, which was especially true for plants growing in close proximity to the infected plants. The occurrence of horizontal transmission of endophytes has not been previously demonstrated.     

A novel method for growing Arabidopsis thaliana plants hydroponically

In this report we describe the development of a simple system for growing individual Arabidopsis plants hydroponically under environmental conditions which are simple to maintain while maximizing growth and development. The system consists of a Life Raft Float Unit with a 14–20 mm sponge inserted into its center; this unit is placed into a Magenta GA7 vessel containing Arabidopsis nutrient solution. Plants grown in this experimental system do not require aeration, 125 μmol m⁻² s⁻¹ supports vigorous plant growth, 1/4 to 1/8 strength Arabidopsis nutrient solution promotes maximal growth while higher or lower levels have adverse effects and temperatures between 18 and 24°C were found to be optimal. Plants grown under these conditions exhibit physiological factors such as time to flowering and overall appearance similar to those grown in potting media. The low maintenance method described in this paper provides an alternative to existing hydroponic methods used to grow Arabidopsis . Adaptation of this system for growing large numbers of plants in 1 container is also discussed.     

Deciphering the ontogeny of a sympodial tree

This paper addresses the identification and characterization of developmental patterns in the whole structure of a sympodial species, the apple tree. Dedicated stochastic models (hidden variable-order Markov chains) were used to (i) categorise growth units (GUs) on the basis of their morphological characteristics (number of nodes and presence/absence of flowering) and position along axes, (ii) analyse dependencies between successive GUs and (iii) identify repeated patterns in GU sequences. Two successive phases, referred to as “adolescent” and “adult”, were identified in two apple tree cultivars. In the adolescent phase, “very” long monocyclic GUs were followed by long polycyclic GUs, whereas in the adult phase medium GUs were preferentially followed by short GUs. Flowering GUs constituted a preferential pathway between vegetative GUs of decreasing vigour (long, medium and short) and generated patterns that were interpreted with respect to fruiting regularity. The proposed modelling gave a global and quantitative picture of the two-scale structuring of apple tree ontogeny: a coarse scale corresponding to the succession of the previously mentioned phases and a fine scale corresponding to the alternation between flowering and vegetative GUs. This led us to propose a synthetic scheme of apple tree ontogeny that combines growth phases, polycyclism and flowering, and which could be transposed to other sympodial trees.     

Patterns of vegetative growth and reproduction in relation to branch orders: the plant as a spatially structured population

The patterns of vegetative growth and reproduction in relation to orders of terminal branches were examined in the evergreen woody plant, Eurya japonica. The branch order number was determined centrifugally. The trunk was given order number 1; branches issuing directly from the trunk were order 2; branches growing on order 2 branches were order 3, and so on. The results of this study show the differential patterns of vegetative growth and reproduction in relation to the branch orders. Lower-order shoots of terminal branches grew more, but produced few flowers. On the other hand, for the higher-order terminal branches, shoot growth was very limited but flowering was more intense. The results show that a tree can be interpreted not as a mere population of equivalent modules but as a spatially structured population. Thus, it is essential to consider the position of modules within the branch system when patterns of vegetative growth and reproduction are examined. It is hypothesized that the difference in the opportunity cost in relation to the branch orders is the main cause of the spatial structure for patterns of vegetative growth and reproduction. Furthermore, for same-order terminal branches, current-year shoot elongation was independent of flowering intensity. These results suggest that this species only invests resources in reproduction that are surplus to its requirements for the functions associated with survival, such as growth and/or storage. Received: 22 July 1999 / Accepted: 12 January 2000     

Growth of Halimium halimifolium under simulated and natural browsing in the Doñana National Park (SW Spain)

Abstract. The annual cycle of vegetative growth in the Mediterranean shrub Halimium halimifolium (Cistaceae) subjected to simulated and natural browsing on the stabilized sands of Doñana National Park (SW Spain) is described. In a drier area without herbivory (Monte Intermedio) plants were subjected to different intensities of clipping. In a more humid area with high herbivory pressure (Monte Negro) plants were isolated by cages. Plants were monitored monthly from February to November 1994. Vegetative growth starts in March and ends in June or July, according to temperature and water availability. Plants intensely clipped and plants subjected to natural browsing responded maximally regarding shoot length, and number of leaves on main shoots and branches. Clipped plants, however, did not reach the height and cover of controls.     

Growth pattern and age determination for Cecropia sciadophylla (Urticaceae)

Cecropia species, ranging from Mexico to northern Argentina and the West Indies, are pioneer trees that colonize cleared areas with high light. To determine their ages to help pinpoint the date of the area's disturbance, we need to understand their developmental and architectural changes over time. The simple architecture of Cecropia conforms to the model of Rauh; that is, it has orthotropic axes with lateral flowering and rhythmic branching. The axes are made of a succession of nodes and internodes whose length and associated lateral productions remain measurable for years. Thus, by describing the tree trunk node by node, we can depict the sequence of events involved in tree development. For 25 trees of C. sciadophylla, from two stations in French Guiana and Colombia, we recorded internode length and any presence of branches, and flowers for each node. Using autocorrelation coefficients, we found a high periodicity in flowering and branching, with inflorescences at every 25 nodes, stages of branches spaced by a multiple of 25 nodes, and alternation of long and short nodes every 25 nodes. Considering that flowering is annual for many Cecropia species, the main conclusion of this work is that C. sciadophylla has strong annual growth, branching, and flowering rhythms. In addition, the age of the tree can be estimated retrospectively by observing its adult morphology.     

The position of localized soil compaction determines root and subsequent shoot growth responses

Plants growing in soils typically experience a mixture of loose and compact soil. The hypothesis that the proportion of a root system exposed to compact soil and/or the timing at which this exposure occurs determines shoot growth responses was tested. Broccoli (Brassica oleracea var. italica cv. Greenbelt) seedlings were grown in pot experiments with compact, loose and localized soil compaction created by either horizontal (compact subsoils 75 or 150 mm below loose topsoil) or vertical (adjacent compact and loose columns of soil) configurations of loose (1.2 Mg m(-3)) and compact (1.8 Mg m(-3)) soil. Entirely compact soil reduced leaf area by up to 54%, relative to loose soil. When compaction was localized, only the vertical columns of compact and loose soil reduced leaf area (by 30%). Neither the proportion of roots in compact soil nor the timing of exposure could explain the differing shoot growth responses to localized soil compaction. Instead, the strong relationship between total root length and leaf area (r(2)=0.92) indicated that localized soil compaction reduced shoot growth only when it suppressed total root length. This occurred when isolated root axes of the same plant were exposed to vertical columns of compact and loose soil. When a single root axis grew through loose soil into either a shallow or deep compact subsoil, compensatory root growth in the loose soil maintained total root length and thus shoot growth was unaffected. These contrasting root systems responses to localized soil compaction may explain the variable shoot growth responses observed under heterogeneous conditions.     

The role of colony morphology and substratum inclination in the success of Millepora alcicornis on shallow coral reefs

 Millepora species are conspicuous members of shallow coral reefs where they occupy a variety of substrata and produce morphologically complex skeletons. This study focuses on the roles of growth on vertical and horizontal surfaces and the production of encrusting bases and branches (a “sheet-tree” morphology) for the success of the Millepora alcicornis on coral reefs. The effects of inclination were investigated by comparing the size and growth rates of M. alcicornis on vertical and horizontal surfaces at 3–5 m depth, in St. John, US Virgin Islands. The consequences of morphological complexity were investigated by comparing polyp density, chlorophyll content and biomass between encrusting bases and branches; the role of branches in asexual reproduction was also quantified. Colonies on vertical surfaces had larger encrusting bases, longer perimeters and lower densities of branches compared to those on horizontal surfaces. Growth rates also varied significantly between surfaces, largely because colonies on horizontal surfaces shrank in area while those on vertical surfaces increased in area, albeit slowly. Branches were not specialized in comparison to encrusting bases in terms of the density of dactylozooids and gastrozooids, chlorophyll content and biomass, but they were effective asexual propagules. During one storm, 79% of the branches were removed from colonies of M. alcicornis, and 4% attached to the substratum to produce new colonies at a density of ≈0.5 colonies.m^-2. Anecdotal observations suggest that such storms rarely damaged encrusting bases on vertical surfaces, but often destroyed those on horizontal surfaces. Thus, the encrusting bases on vertical surfaces are likely to be large because of greater age rather than faster growth, while those on horizontal surfaces are likely to be small because they are relatively young and short lived. These findings suggest that the success of M. alcicornis is a result, in part, of the beneficial consequences of their “sheet-tree” morphology, that supports: (a) slow growth and resistance to wave damage of encrusting bases on vertical surfaces, and (b) the use of branches as asexual propagules. Accepted: 24 November 1998     

Morphology and growth of deciduous and evergreen broad-leaved saplings under different light conditions in a Chinese beech forest with dense bamboo undergrowth

This study compared the morphological and growth adjustment of saplings from three shade- tolerant canopy species (Castanopsis lamontii, Lithocarpus hancei and Fagus lucida; Fagaceae) under different light conditions in a Chinese beech forest with dense bamboo undergrowth. Only F. lucida is deciduous, and it had the most flexible morphology. In shade, F. lucida had flat or bent topshoots and horizontal branches to maximize light interception, while in conditions of high light intensity, it formed vertical topshoots to promote growth in terms of height, and upright branches to mitigate excessive sun exposure on the leaves. In contrast to F. lucida (beech), the evergreen species always had vertical topshoots regardless of light conditions. In shady conditions, the evergreens had greater annual growth rates in terms of both height and diameter than the beech, and between the evergreens, the species bearing plagiotropic branches grew faster in diameter than the species bearing orthotropic branches. The evergreen trees had thicker leaves and thicker stems compared to the beech. It was concluded that the evergreen saplings have advantages over beech saplings in terms of current growth in the forest understorey; whereas, morphological and growth flexibility in the beech aids in its persistence in the understorey.     

Initial growth of Brazilian pine (Araucaria angustifolia) under equal soil volumes but contrasting rooting depths

Araucaria angustifolia is a critically endangered tall tree species of valuable wood, and field observations led to the suggestion that limitations imposed to the vertical growth of its tap root system greatly restrict the height of mature individuals. However, experimental studies dealing with the effects of soil depth on the species growth are mostly lacking. This study evaluated and compared the growth responses of young plants of A. angustifolia to distinct rooting depths but same soil volumes. Seeds were planted in pots of different heights and diameters, all containing 3 liters of soil mixture. Plants were submitted to four available rooting depths: 65 (T1), 35 (T2), 20 (T3), and 10 (T4) cm. There were eight experimental units in each treatment, arranged in a randomized complete block design, each block containing two units per treatment. Contrary to what was expected, the T3 and T4 plants had accumulated more mass and attained the same height as the other two groups, after a 10-month growth period in a green house. Those plants also had thicker stems, longer shoot branches, and thicker and longer lateral roots, which were interpreted as compensatory responses to increase plant anchorage and stability. The inverse relationship between rooting depth and plant mass was attributed to a down-regulation of shoot growth because or restricted lateral space and/or poor soil aeration of the longer and narrower pots. This experiment allowed us to demonstrate that is not the possibility of the tap root to grow deep into the soil that ensures a better growth to plants of A. angustifolia: provided that the offer of soil volume and resources are the same, the vertical extension of the tap root does not result in greater growth of the plants. In fact, much greater growth impairment is expected from lateral than from vertical restriction to root growth.     

Interpreting Plant Responses to Clinostating: I. MECHANICAL STRESSES AND ETHYLENE

The severe epinasty and other symptoms developed by clinostated leafy plants could be responses to gravity compensation and/or the mechanical stresses of leaf flopping. Epinasty in cocklebur (Xanthium strumarium L.), tomato (Lycopersicon esculentum Mill.), and castor bean (Ricinus communis L.) is delayed by inhibitors of ethylene synthesis and action (aminoethoxyvinylglycine and Ag⁺), confirming the role of ethylene in clinostat epinasty. To test the possibility that clinostat mechanical stresses (leaf flopping) cause ethylene production and, thus, epinasty, vertical plants were stressed with constant, gentle, horizontal, or vertical shaking or with a quick, back-and-forth rotation (twisting). Clinostat leaf flopping was closely approximated but with a minimum of gravity compensation, by turning plants so their stems were horizontal, rotating them quickly about the stem axis, and then returning them to the vertical, repeating the treatment every four minutes (clinostat rotation time). None of these mechanical stresses produced significant epinasties, but vigorous hand-shaking (120 seconds per day) generated minor epinasties, as did Ag⁺ applied daily (concentrations high enough to cause leaf browning). Plants gently inverted every 20 minutes developed epinasty at about the same rate and to about the same extent as clinostated plants, but plants inverted every 20 minutes and immediately returned to the upright position did not become epinastic. It is concluded that clinostat epinasty is probably caused by disturbances in the gravity perception mechanism, rather than by leaf flopping.     

Coarse- versus fine-grained water stress in Arabidopsis thaliana (Brassicaceae)

The effects of coarse vs. fine-grained variation in water regime on 13 accessions of Arabidopsis thaliana were compared and it was found that the scale of environmental variation can lead to differences in which traits are affected and in the magnitude and direction of effect. Coarse-grained (between individual) variation was studied by comparing plants that received high or low amounts of water on a daily basis. Fine-grained (within individual) variation was distributed across the coarse-grained treatments; plants in the fine-grained treatment received the same amount of water per week as the corresponding high and low coarse-grained treatments; however, in the fine-grained treatments, plants received their entire weekly water allotment over 2 days. The number of leaves produced, days to bolting, length of bolt, number of basal and lateral branches, and survival to 30 days after bolting were measured and analyzed by ANOVA. Plants grown in high water generally produced more leaves, taller main axes, more branches and had increased survival, relative to those in low water. Bolting date showed a significant genotype specific effect of water level. Plants grown under fine-grained variation in watering had taller main axes relative to constant water. There were significant interactions between both types of variation for bolting date, main axis height, and survival. Principal components for all traits were loaded such that the components themselves were also independently affected by genotype, water level, variability of water level (grain), and level-by-grain interactions in ways that were largely predicted by their component traits. Overall, the effects of fine-grained variation were subtler than those of coarse-grained variation: fewer traits responded, and the magnitude of the responses was smaller. Nevertheless, the responses to fine-grained variation are distinct from those of coarse-gained variation, differing with respect to which traits respond and in the direction of response, and must therefore be treated as independent sources of environmental variation.     

THE NEW GENUS AND SPECIES OSSIELLA PACIFICA (GRIFFITHSIEAE, RHODOPHYTA) FROM HAWAII AND NORFOLK ISLAND, PACIFIC OCEAN

Ossiella pacifica gen. et sp. nov. is described from sub tidal habitats (5–19 m) in the central (Hawaiian Islands) and southwestern (Norfolk Island) Pacific Ocean. Plants consist of limited prostrate axes that rapidly become erect and form ecorticate, subdichotomously branched axes bearing up to seven (mostly six) di-/to trichotomously branched, pigmented, determinate, quickly caducous whorled laterals from subapical axial cells. Two to five tetrasporangza are borne directly on the inflated basal cells of pigmented determinate laterals. One to two spermatangial fascicles are similarly placed in male plants. Subapical procarps are borne on a three-celled fertile axis, which occupies the same position as an indeterminate branch, being itself displaced laterally by the continued growth of the indeterminate axis. Procarps are bicarpogonial, the sterile cell normally associated with the supporting cell in procarps of the Griffithsieae being converted into a functional four-celled carpogonial branch . Ossiella is compared with the other membus of the tribe, and a dichotomous key to the genera is offered. On morphological grounds , Ossiella seemingly forms a perfect intermediary link along the phylogenetic lineage between the eastern Australian genus Baldockia A. Millar, the eastern American genus Calliclavula G. W. Schneid, and the widespread Anotrichium Nägeli .     

In vitro propagation of three <Emphasis Type="Italic">Agave</Emphasis> species used for liquor distillation and three for landscape

In vitro bud clusters of Calathea orbifolia (Linden) Kennedy were obtained and subcultured in semi-solid (agar) medium and temporary immersion system (TIS) for 12 weeks. Uniform young plants were selected and transferred to soilless mix in a growth chamber for ex vitro acclimatization during 35 days, followed by growing in a shaded greenhouse for 65 days. Comparison of in vitro leaf anatomy, ex vitro photosynthetic behaviors and growth was made between two cultural systems. Plants in TIS produced thicker leaf chlorenchyma and aquiferous parenchyma, lower stomatal frequency and more epicuticular wax than did those in semi-solid medium. Plants from semi-solid medium had consistently lower leaf Fv/Fm values than plants from TIS. Leaf Fv/Fm value in plants from TIS decreased to 0.65 at day 7 after transfer and increased soon up to 0.76 thereafter. In contrast, leaf Fv/Fm value in plants from semi-solid medium reduced to 0.27 at day 7 after transfer and increased slowly up to 0.68 at day 35. During ex vitro acclimatization, plants in TIS had substantial higher photosynthetic rates than plants in semi-solid medium. Plants from TIS had subsequent higher leaf area, fresh and dry weights than plants from semi-solid medium.