Crown architecture of grafted Stone pine (Pinus pinea L.): shoot growth and bud differentiation

The singular umbrella-like crown shape of Stone pine can be interpreted as a consequence of primary shoot-growth patterns and posterior axis differentiation due to differential secondary growth and down-bending of branches. This paper centres on the first aspect, analysing the growth, branching and flowering behaviour of about 5,000 individual shoots on 27 grafted Stone pines. The data measurement on standing trees allowed to study correlations of topologic and geometric variables in the shoot and their ancestors. The only significant correlations were found with parameters of the mother shoot formed the previous year and with the number of cones born 3 years before by the respective ancestor. The fitted relationships between geometric and topologic shoot and branch variables are the first step of a structural model construction that can be completed with functional components like a radiation and a carbon allocation submodel, stressing the importance of the heavy Stone pine cones as carbon sinks, with a total annual allocation similar to stem wood. In conclusion, the Stone pine crown shape emerges as consequence of the lack of initial vigour differentiation between stem and main-branch apical meristems that favour the generalized sylleptic reiteration in the open-grown trees.     

Influence of leaf size on tree architecture: first branch height and crown dimensions in tropical rain forest trees

 First branch height is an important attribute of sapling architecture, as it defines the height at which prolonged lateral growth is possible. First branch height, measured on saplings of 70 species in tropical rain forests of Australia, Costa Rica, Panama, and Sabah, Malaysia, was highly correlated with leaf blade and petiole length. The observed relationship, first branch height ∝ blade length × (petiole length)^0.5, implies that the ratio of first branch height to blade length increases somewhat with increasing leaf size, among species with a given ratio of petiole to blade length. Orthotropic species, with more or less radially symmetric arrangements of leaves on ascending axes, had a mean first branch height of 7x that observed for plagiotropic species, with planar leaf arrangements. The greater first branch height of orthotropic species was associated with their larger leaves and longer petioles. Plagiotropic species had wider crowns than orthotropic species in the sapling stage, as assessed at the Costa Rican site. Thus, leaf dimensions influence the dynamics of crown construction (or visa versa), as well as affecting leaf energy balance and gas exchange. Received: 5 September 1997 / Accepted: 3 March 1998     

The effect of crown position and date of sampling on biomass,nutrient concentrations and contents of needles and shoots in European larch

 The nutrient concentrations and contents of needles and shoots of 22-year-old European larch (Larix decidua Mill.) were evaluated with respect to crown position, age of tissues and sampling date during a complete growing season. Concentrations of N, P, K, Ca, Mg and Zn in the needles and of N, P and K in the shoots differed significantly among the dates of sampling. The concentrations of N and Mn in the needles and all nutrients in the shoots (except Mg) also differed significantly with crown position. Maximum needle biomass was observed in the middle crown position (55% of the total) and maximum shoot biomass, in the lower crown position (52% of the total). Maximum needle and shoot nutrient contents were observed in the middle position of the living crown for long shoot, short shoot-1, short shoot-2, short shoot-3 and, short shoot-4 age classes while highest contents for short shoot-5 and short shoot-6 age classes were observed in the lower crown position. Biases up to 42% for Mg in the needles and 200% for K in the shoots were obtained when only long shoot tissues are used for content evaluation. For needles and shoots, Mg and K are more difficult nutrients to evaluate. A sampling methodology is proposed for evaluating nutrient contents of the living crown. Accepted: 10 August 1995     

A simulation model of tree architecture development based on growth response to local light environment

A new model of three-dimensional tree architecture development was made, in which the growth of branches depends on their local light environment. The unit of the tree architecture is a linear stem called the branch unit (BU). Current-year BU's have leaves at their distal end. The local light environment is calculated considering mutual shading among leaved BU's. During the growth of a model tree, the number of leaved BU's increases and mutual shading becomes severe. The shadling leads to production of fewer new BU's and the death of some BU's, both of which restrain the overcrowding of BU's. The shape of the crowns of trees grown in a model forest stand varies with their position in the stand in a similar way as observed in real forests. This also results from the growth response of BU's to their local light environment. A model tree in which the photoassimillates were shared equally among the BU's was much disadvantaged in competition with the original model trees.     

Plasticity in leaf-area density within the crown of Aucuba japonica growing under different light levels

We assessed leaf-area density (LAD; m² m⁻³) within the crown of Aucuba japonica (Cornaceae) growing under different light regimes and analyzed the components of crown architecture that most influenced variation in LAD. At a whole-crown level, extension-unit (EU) density (EUs/m³) had the greatest impact on LAD. The number of leaves per unit EU length and EU length had a wide range of impacts depending on the degree of crowding of foliage on the EU. Leaf size had a lesser impact on LAD. LAD was higher in the uppermost crown and declined towards the base. The non-uniformity of LAD among crown layers was much greater under high irradiance. Individuals under high irradiance achieved greater LAD by increased branching, well-marked EU dimorphism and a larger number of leaves per unit EU length; the reverse was true for the individuals under low irradiance. We identified two distinct modes of growth response to light regime. Under high irradiance, individuals responded by differential growth between the layers of crowns with the lower crown suppressed and growth in the upper crown increased. Conversely, shaded individuals did not respond by differential growth between crown layers.     

Bud morphology and shoot growth dynamics in two species of Mediterranean sub-shrubs co-existing in gypsum outcrops

BACKGROUND AND AIMS: Understanding the effects of the environment on the morphology and shoot growth activities of plants is crucial to identifying plant ecological strategies. This study analysed the bud morphology, bud activity, shoot growth dynamics and shoot water content at full hydration (WC(h)) of two species of Mediterranean sub-shrubs, Lepidium subulatum and Linum suffruticosum, co-existing in gypsum outcrops in north-east Spain. METHODS: Sampling was conducted monthly over 2 years in one population per species. Buds were dissected under a stereo-microscope. Shoot growth was measured as the mean increase in shoot length of 15 marked individuals between two consecutive samplings. Bud activity was studied following the variations in the number of leaf primordia shorter than 1 mm and longer than 0.025 mm in the buds. KEY RESULTS: Both species bore naked buds and displayed discontinuous seasonal patterns of shoot growth, leaf primordia formation and WC(h). The number of leaf primordia in the bud peaked before the beginning of shoot expansion. In both species, organogenesis and expansion were uncoupled throughout the year. The time lapse between these two processes varied throughout the year, and was greatest for those elements differentiated in autumn. WC(h) was more closely related to shoot expansion than to organogenesis. CONCLUSIONS: Both species displayed similar bud morphology and similar seasonal patterns of bud and shoot growth, and WC(h) as a result of the strong seasonality of the Mediterranean climate in gypsum outcrops. The beginning of the spring period of expansion of long branches coincided with maximum values of WC(h), while the rest period of summer matched minimum values. These results support the hypothesis that the growth of long branches is strongly related to WC(h).     

Frequent fires alter tree architecture and impair reproduction of a common fire‐tolerant savanna tree

• Several Cerrado tree species have traits and structures that protect from fires. The effectiveness of a trait depends on the fire regime, especially the frequency. We used Vochysia elliptica, a common Cerrado tree, as a model to test whether different fire frequencies alter crown architecture and flower, fruit and seed production.
• We analysed the effect of fire on the production of inflorescences, fruits and seeds, as well as seed germination and tree architecture of 20 trees in each of three plots of a long‐term ecological experiment managed with different fire regimes: burned every 2 years (B), burned every 4 years (Q) in mid‐dry season and an area protected from fire (C).
• We found a large negative effect of fire frequency on crown architecture and on flower and fruit production. Trees in C and Q had significantly more main branches and a larger crown area than trees in B. At its peak, a tree in C was expected to produce 2.4 times more inflorescences than Q, and 15.5 times more than B, with similar magnitudes for fruits. Sixty per cent of trees in B and 10% in Q produced no fruits.
• The differences in architecture might explain the reduction in sexual reproduction due to a smaller physical space to produce flowers at the branch apices. Resource limitation due to plant investment to replace burned vegetative parts may also decrease sexual reproduction. Our results indicate potentially severe consequences of high fire frequencies for population dynamics and species persistence in Cerrado communities.

     

The effect of shoot architecture on hydraulic conductance in beech (Fagus sylvatica L.)

 Shoot hydraulic conductance was measured in beech (Fagus sylvatica L.) that had previously been exposed to high levels of nitrogen input. Whole-shoot hydraulic conductance, conductance per unit pressure gradient and leaf specific conductance were negatively correlated with the number of bud scars per unit length, a morphological parameter of tree decline. We propose a negative feedback mechanism by which stress induced alterations in shoot morphology can cause a lasting reduction of tree vigour. Received: 2 July 1997 / Accepted: 25 June 1998     

Following the initiation and development of individual leaf primordia at the level of the shoot apical meristem: the case of distichous phyllotaxis in Begonia

BACKGROUND AND AIMS: By using the technique of replicas of a developing apex it is possible to obtain a direct measure of phyllotactic parameters (plastochrone and platochronic ratio) involved in the initiation of two successive primordia at the level of the SAM. The goal of this study is to compare, in a real time setting, the value of phyllotactic parameters in distichous systems using Begonia as a case study, with the value of the same parameters in spiral phyllotactic systems. METHODS: To determine the real-time sequence of events at the level of the SAM, replicas were made of the developing apex at different intervals using previously described techniques. Impression moulds were made at 24-h intervals. The following phyllotactic parameters were measured: plastochrone, angle of divergence, plastochrone ratio and ratio between the diameter of the leaf and the apex. RESULTS: The time between the appearance of two successive leaves is 15-20 d. The average value of the plastochrone ratio (R) is 1.3, and the ratio of the leaf to the diameter of the apex (Gamma) is 2.5. The angle of divergence varies from 165 masculine to 180 masculine. The speed of advection of the primordium from the apex, varies from 0.28 to 0.37 microm d(-1). CONCLUSIONS: The speed of advection of primordia in Begonia is lower than that of Anagalis. This is not in accordance with theoretical simulations that predict the opposite. In Begonia, the plastochrone ratio does not reflect the real time of appearance of two successive primordia. The time separating the appearance of two primordia is not directly related to the distance of these two primordia from the centre of the apex but is related instead to the enlargement of leaves.     

The role of sucrose during maturation of black spruce (Picea mariana) and white spruce (Picea glauca) somatic embryos

The present study was conducted to understand the role of sucrose in the medium on the maturation of black spruce and white spruce somatic embryos. A maturation medium containing 6% sucrose, which hydrolyzed into glucose and fructose, gave significantly more embryos than a medium containing 3.16% of each glucose and fructose. Preventing the complete sucrose hydrolysis by a daily transfer of the tissues onto fresh medium significantly decreased the yield of somatic embryos compared to when sucrose was allowed to complete its hydrolysis. This reduction was not due to the manipulation of the tissues during the transfer, since a daily in situ transfer did not affect embryo production. To verify if the better embryo production observed on a medium containing 6% sucrose was due to the increasing osmotic pressure of the medium, this increasing osmotic pressure was simulated with a sequence of media containing different concentrations of glucose and fructose. Unexpectedly and for both species, this simulation did not improve somatic embryo production, which stayed similar to the one obtained on constant osmotic pressure. To understand these results, embryos produced on the different treatments were analyzed in terms of sucrose, glucose, fructose and starch levels and protein contents. The embryo carbohydrate content was independent from the carbohydrate used in the maturation medium. However, embryos matured on 6% sucrose allowed to hydrolyze during the maturation period contained significantly more soluble and insoluble proteins than embryos matured on any other treatment. Furthermore, embryos with a higher protein content also exhibited a higher epicotyl appearance frequency. The role of sucrose as a regulatory factor during the maturation of spruce somatic embryos is discussed.     

Effects of long-term CO2 enrichment and nutrient availability in Norway spruce. I. Phenology and morphology of branches

 Branches of 30-year-old Norway spruce [Picea abies (L.) Karst.] trees were enclosed in ventilated, transparent plastic bags and flushed with air containing ambient (A≈370 μmol CO₂ mol^–1) or ambient plus 340 μmol CO₂ mol^–1 (EL). Light-saturated photosynthesis was on average 56% higher in EL compared to A. Branch phenology and morphology were strongly related to nitrogen concentration (mg g^–1 dry mass) in the foliage and to elevated temperatures in the bags, but no direct effect of EL was found. In 1995, budbreak occurred on average 4 days earlier in the bags compared to the control branches, which was partly explained by the temperature elevation in the bags. No nutrient or EL effect on budbreak was found. Increases in temperature and nitrogen supply increased shoot growth: together they explained 76% of the variation in the extension rate, 63% of the variation in extension duration and 65% of the variation in final length of leading shoots. Shoot morphology was altered both by increased nitrogen availability and by the enclosure induced environmental changes inside the bags, leading to reduced mutual shading between needles. Specific needle area (SNA) was lower in EL, but this was related to lower nitrogen concentrations. Total dry mass of the branches was unaffected by EL. It is concluded that treating individual branches of Norway spruce with elevated CO₂ does not increase branch growth. The nutrient status of the branch and climate determine its growth, i.e. its sink strength for carbon. Increased export of carbohydrates to the rest of the tree is probable in EL treated branches. Received: 20 July 1998 / Accepted 8 October 1998     

A tree of many faces: Why are there different crown types in Norway spruce (Picea abies [L.] Karst.)?

Norway spruce (Picea abies [L.] Karst.) has a pronounced ability to create different crown types embracing strongly hypotonic, epi-hypotonic, strongly amphitonic types as well as respective intermediate ones. Data of Holzer and Schultze (1987) were reanalyzed in order to identify major environmental components that may shape ecotypes and contribute to Gruber's (1989) hypothesis that phenotypic plasticity is different among different crown types. Environmental variables and crown types were assessed by Principal Components Analysis. The first principal component explained 74% of the variation that was mainly loaded by different temperature variables and altitude while the second principal component explained additional 23% mainly loaded by precipitation variables. Orientation had a statistically significant but small effect. Covariance analysis demonstrated that age had modified crown type in a way that more hypotonic types were phenotypically more variable. Overlaps between crown-type distributions were evaluated by Schoener's Index, which may range from ‘zero’ (no ecotypic overlap) to ‘one’ (complete ecotypic overlap). In the present paper this index resulted in pairwise values varying from 0.21 to 0.86. The ecotypic overlap matrix was symmetric, i.e. ecotypic pairs increased gradually with stepwise crown-type graduation. We discussed the adaptation strategy of Norway spruce based on our results and propose that adaptation in this species regarding crown architecture is mainly caused by adaptive differentiation in higher altitudes while in lower elevations phenotypic plasticity is the dominating factor.     

Synthesis of di- and trisaccharides incorporating a crown ether macrocycle

Di- and trisaccharides incorporating a non-reducing hexopyranose residue linked to a sugar bearing a 18-crown-6-ether were synthesized by the trichloroacetimidate method. Mainly β-glycosides were isolated when secondary alcohols were used as acceptors in the presence of (C₂H₅)₂O·BF₃. Deprotection left four novel structures which were on one hand able to complex cationic species and on the other hand were able to be recognized by lectins. They are the first representatives of a new class of water-soluble cation vectors.     

Crown alterations induced by decline: a study of relationships between growth rate and crown morphology in beech (Fagus sylvatica L.)

One of the first symptoms expressed by declining trees is reduced growth in stem diameter and length increment. The possibility of a relationship between length increment and crown thinning in beech (Fagus sylvatica L.) was investigated by developing a computer model to simulate first order branching patterns of the apical 2 m of monopodially branching beech trees, 70–100 years old, for a range of length increment rates. The model was based on values for branching angle, main axis and branch length increment, number of branches produced per year and branch mortality rates for six healthy and declining trees. Shoot growth rates in the apical 2 m of the sample trees ranged from about 5 cm/year (decline class 3) to 43 cm/ year (healthy). Simulations of branching patterns in the apical 2 m of trees growing at different rates indicated that, when growth rate exceeded about 20 cm/year, total first order branch length and area explored were independent of growth rate. When growth rates fell below this value there was a reduction in total area explored and first order branch length due primarily to the formation of fewer branches. More acute branching angles contributed to a reduction in the area explored. Growth rate-related crown thinning could increase the risk of bark necrosis and secondary pathogen infection during dry and/or hot spells.     

Apple shoot architecture: evidence for strong variability of bud size and composition and hydraulics within a branching zone

* In the apple tree (Malus domestica), shoot architecture - the distribution of lateral bud types and growth along the parent shoot - has been extensively investigated. The distal zone of a shoot is characterized by a high proportion of vegetative or floral axillary branches mixed with latent buds and aborted laterals. The hypothesis tested here was that bud development was related to hydraulic conductance of the sap pathway to the bud, independently of an acrotonic (proximal vs distal) effect. * The distal zone of 1-yr-old shoots was studied on five cultivars for bud size and composition (number of appendages) and hydraulic conductance before bud burst. * Bud size, composition and hydraulic conductance were highly variable for all cultivars. A positive correlation was demonstrated between both the number of cataphylls and green-leaf primordia, and hydraulic conductance. Cultivar and bud size affected the intercept of these relationships more than the slope, suggesting similar scaling between these variables, but different hydraulic efficiencies. A great proportion of small buds were also characterized by null values of hydraulic conductance. * This study suggests that hydraulically mediated competition exists between adjacent buds within the same branching zone, prefiguring the variability of lateral types in the following growing season. It is hypothesized that this developmental patterning is driven by hydraulic characteristics of the whole metamer, including the subtending leaf, during bud development.     

Effect of ecosystem warming on boreal black spruce bud burst and shoot growth

The boreal forest is predicted to experience the greatest warming of any forest biome during the next 50–100 years, but the effects of warming on vegetation phenology are not well known. The objectives of this study were to (1) examine the effects of whole ecosystem warming on bud burst and annual shoot growth of black spruce trees in northern Manitoba, Canada and (2) correlate bud burst to cumulative degree-days (CDD). The experimental design was a complete randomized block design that consisted of four replicated blocks. Each replicate block contained four treatments: soil warming only (heated outside, HO), soil and air warming (heated inside, HI), control outside (no chamber, no heating, CO), and inside a chamber maintained at ambient conditions (no soil or air warming, control inside, CI). Bud burst was measured during the first and second years of the experiment, starting in 2004, and annual shoot growth was measured for the first 3 years (2004–2006) of the study. On average, shoot bud burst occurred 11 and 9 days earlier in 2004 and 2005, respectively, for HI than for other treatments. However, mean CDD required for bud burst for HI was within the standard deviation of CO for both years. In year 1 of the treatments, shoot bud burst occurred earlier for HI than other treatments (CI, CO, HO), but final shoot length of HI trees was less than in CO trees. In the second year of warming, final shoot length was not different for HI than CO. By the third year of warming final shoot length was significantly greater for HI than all other treatments. Empirical results from this study suggest that soil and air warming causes an earlier bud burst for all years of observation and greater shoot lengths by the third season of warming. A longer growing season and greater annual shoot growth should increase carbon uptake by boreal black spruce trees in a warmer climate.     

Inheritance of plastids in interspecific hybrids of blue spruce and white spruce

Summary Chloroplast DNA (cpDNA) was purified from blue spruce (Picea pungens Engelm.) and white spruce [P. glauca (Moench) Voss], and was digested with several different restriction endonucleases. Restriction fragment length polymorphisms (RFLPs) were identified that differentiated the cpDNA of both species. Intraspecific conservation of the RFLPs that differentiated each species was confirmed by examining trees from across the natural range of each species. Ten F₁ hybrids were examined, and the cpDNA from each showed the banding pattern of the paternal species. Cloned Petunia cpDNA containing part of the rbcL gene hybridized to polymorphic bands, while a cloned maize mtDNA probe of the coxII gene failed to hybridize to any band.