Shoot Expansion Research Articles

Preferential allocation of carbohydrate reserves belowground supports disturbance-based management of American chestnut (Castanea dentata)

Non-structural carbohydrates (NSCs) are critical for the survival of trees, but the ability to accurately predict NSC levels for a given forest tree species is lacking. We evaluated NSC dynamics in American chestnut (Castanea dentata), a species of high restoration interest, to test the conventional model of seasonal and inter-organ dynamics and to facilitate informed conservation efforts. Chestnut trees were sampled over the course of one year at different phenological stages. Then, organ-specific NSC concentration data were paired with biomass estimates from a custom-built allometric model to generate NSC pool sizes. Organ-level NSC concentrations and pools generally peaked at leaf fall (October) and were lowest during shoot expansion (June), although interactions between organ type and collection period drove variation in pool sizes. Whole-tree NSC pools increased from 2.47 ± 0.42 kg at shoot expansion to 4.29 ± 0.65 kg at leaf fall. Coarse roots were the most important NSC reservoir, accounting for 46.5% − 56.6% of the total whole-tree NSC reserves, depending on the time of year. Coarse root NSC pools were larger and more dynamic than in previous studies with other temperate deciduous trees, and they were the primary supplier of NSCs to support spring leaf-out. Preferential belowground NSC allocation and the ability to mobilize root NSCs to fuel growth and metabolism suggest that chestnut could thrive under disturbance-based management.

Phenology explains different storage remobilization in two congeneric temperate tree species with contrasting leaf habit

The dependence of trees on carbon and nutrient storage is critical to predicting the forest vulnerability under climate change, but whether evergreen and deciduous species differ in their use and allocation of stored resources during spring phenology is unclear. Using a high temporal resolution, we evaluated the role of spring phenology and shoot growth as determinants of the carbon and nutrient storage dynamics in contrasting leaf habits. We recorded the phenology and shoot elongation and determined the concentrations of total non-structural carbohydrates (NSCs), starch, soluble carbohydrates, nitrogen (N) and phosphorus (P) in buds, expanding shoots and previously formed shoots of two sympatric Nothofagus species with contrasting leaf habit. Species reached similar shoot lengths, though shoot expansion started 35 days earlier and lasted c. 40 days more in the deciduous species. Thus, although the deciduous species had a relatively constant shoot growth rate, the evergreen species experienced a conspicuous growth peak for c. 20 days. In the evergreen species, the greatest decreases in NSC concentrations of previously formed shoots and leaves coincided with the maximum shoot expansion rate and fruit filling, with minimums of 63 and 65% relative to values at bud dormancy, respectively. In contrast, minimum NSC concentrations of the previously formed shoots of the deciduous species were only 73% and occurred prior to the initiation of shoot expansion. Bud N and P concentrations increased during budbreak, whereas previously formed shoots generally did not decrease their nutrient concentrations. Late spring phenology and overlapping of phenophases contributed to the greater dependence on storage of proximal tissues in the studied evergreen compared with deciduous species, suggesting that phenology is a key determinant of the contrasting patterns of storage use in evergreen and deciduous species.

Evolutionary and ecological significance of photosynthetic organs inPhyllocladus(Podocarpaceae)

AbstractThe structure of phylloclades and true leaves in Phyllocladus was investigated with emphasis on function, ecology and evolution. Only in the earliest ontogenetic stages are true, needle leaves developed. The earliest phylloclades comprise a fusion product of a shoot axis of the first order and its inserted leaves. Later, this is augmented by the expansion of axillary short shoots from the base of some of the fused leaves. Phylloclades of mature individuals are entire short shoot systems, including leaves and shoots, becoming fused with photosynthetic tissue. These phylloclades represent one of the adaptations for increasing functional photosynthetic area that are present in Podocarpaceae. Such adaptations were probably needed because Podocarpaceae are usually medium-sized trees faced with competition from the ever-expanding angiosperm forests at mid to high latitudes in the Southern Hemisphere from the Late Cretaceous, but especially during the Palaeocene–Eocene, when dense and diverse angiosperm-dominated rainforests were common. The data obtained from living species were compared to those from fossil material of Phyllocladus. Phyllocladus with fully developed phylloclades have been in place since at least the early Cenozoic.

Springtime Drought Shifts Carbon Partitioning of Recent Photosynthates in 10-Year Old Picea mariana Trees, Causing Restricted Canopy Development

Springtime bud-break and shoot development induces substantial carbon (C) costs in trees. Drought stress during shoot development can impede C uptake and translocation. This is therefore a channel through which water shortage can lead to restricted shoot expansion and physiological capacity, which in turn may impact annual canopy C uptake. We studied effects of drought and re-hydration on early season shoot development, C uptake and partitioning in five individual 10-year old Picea mariana [black spruce] trees to identify and quantify dynamics of key morphological/physiological processes. Trees were subjected to one of two treatments: (i) well-watered control or (ii) drought and rehydration. We monitored changes in morphological [shoot volume, leaf mass area (LMA)], biochemical [osmolality, non-structural carbohydrates (NSC)] and physiological [rates of respiration (Rd) and light-saturated photosynthesis (Asat)] processes during shoot development. Further, to study functional compartmentalization and use of new assimilates, we 13C-pulse labeled shoots at multiple development stages, and measured isotopic signatures of leaf respiration, NSC pools and structural biomass. Shoot water potential dropped to a minimum of −2.5 MPa in shoots on the droughted trees. Development of the photosynthetic apparatus was delayed, as shoots on well-watered trees broke-even 14 days prior to shoots from trees exposed to water deficit. Rd decreased with shoot maturation as growth respiration declined, and was lower in shoots exposed to drought. We found that shoot development was delayed by drought, and while rehydration resulted in recovery of Asat to similar levels as shoots on the well-watered trees, shoot volume remained lower. Water deficit during shoot expansion resulted in longer, yet more compact (i.e., with greater LMA) shoots with greater needle osmolality. The 12C:13C isotopic patterns indicated that internal C partitioning and use was dependent on foliar developmental and hydration status. Shoots on drought-stressed trees prioritized allocating newly fixed C to respiration over structural components. In conclusion, temporary water deficit delayed new shoot development and resulted in greater LMA in black spruce. Since evergreen species such as black spruce retain active foliage for multiple years, impacts of early season drought on net primary productivity could be carried forward into subsequent years.

Phenotypic Evaluation of a Hybrid Diploid Blueberry Population for Plant Development and Fruit Quality Traits

A diploid blueberry mapping population, used previously to map quantitative trait loci (QTL) for chilling requirement and cold hardiness, was evaluated for several plant development and fruit quality traits. Specifically, the population was phenotyped in a greenhouse for timing of various stages of flower bud, leaf bud and fruit development and for fruit quality traits including weight, diameter, color, scar, firmness, flavor and soluble solids. Phenotypic data was analyzed statistically by analysis of variance, correlation tests, to examine associations of traits, and heritability. Results indicated that the traits were segregating and most were distributed normally in the population. Many of the development traits were correlated, and timing of shoot expansion, early bloom and full bloom was also correlated with the previously evaluated trait of chilling requirement. Some correlations were found among the fruit quality traits as well. For example, weight was highly correlated with diameter, and subjectively measured firmness was moderately correlated with one of the objectively measured firmness traits. In addition, most of the traits showed significant variation across genotypes and across years, and most had moderate to high heritability. Therefore, we conclude that the diploid population should be useful for identifying QTL for many of these traits.

Study on the pattern of vegetative growth in young dioecious trees of Idesia polycarpa maxim

Key messageThe dioeciousIdesia polycarpaall that males and females do not invest in the same way in growth and branching in quantity, type of axes and in time (annual growth and sequence of these events over time).The annual growth of plants is an important indicator for growth and development, especially for younger trees. The aim of this study was to decide the physiological basis for vegetative growth effects on the trunk and crown development in Idesia polycarpa by assessing the effects on variations in bud growth, leaf, and canopy size. This study focused on the annual vegetative growth of young (3-year old) female and male I. polycarpa Maxim trees and their functions are separate. The phenology provides a challenge in the production of resources (seed, oil) and to investigate the effect of sexual specialization. Here we describe the variations between two sexes in terms of vegetative growth in our field studies. The study began in the sprouting season with observations of the gradual growth of the newly sprouting buds. The length of expansion, diameter growth, and leaf production from the terminal bud (TB), lateral terminal bud (LTB) of the first tier of branches (1Y), second tier of branches (2Y), and third tier of branches (3Y) of the trees were measured. The results showed growth differences between female and male groups in the growing year. The length of shoot expansion, diameter, and leaf production were higher for female trees than for male trees. Male trees grew more long and short branches (SB) than the female trees, with large numbers of short branches on the 1Y and 2Y of the male trees. Further investigation needed to analyze factors of annual fluctuation of the shoot expansion of the tree, with more studies investigating complex branching phenomenon, flowering, and fruit production in I. polycarpa Maxim.

Effects of insufficient chilling on budburst and growth of six temperate forest tree species in Ontario

Insufficient winter chilling related to rising temperatures has raised questions about its potential effects on budburst timing (growth initiation) and subsequent tree growth. We quantified budburst timing and growth of seedlings of six Ontario temperate forest tree species after exposure to different levels of winter chilling using controlled forcing experiments. Based on chilling–forcing relationships, chilling requirements for the species tested ranged from 1000 to 1500 weighted chilling hours. Our findings showed that the species’ chilling needs ranked from highest to lowest were yellow birch (Betula alleghaniensis), eastern larch (Larix laricina), eastern white pine (Pinus strobus), red pine (Pinus resinosa), red spruce (Picea rubens), and eastern white cedar (Thuja occidentalis). Species that needed more chilling to release dormancy generally required less cumulative forcing for budburst. The variations in chilling–forcing relationships among species suggest that they would respond differently to temperature changes, resulting in year to year variation in their relative phenology. Insufficient chilling increased cumulative forcing needed for budburst but only extreme chilling deficiency (< 700 weighted chilling hours) caused abnormal budburst and growth, including reduced leaf and shoot expansion, early and erratic budburst in lower branches and stems, and even lack of budburst after 7 months in optimal growing conditions. Overall, our results suggest that based on climate warming projected for this century, insufficient winter chilling is not likely to occur in Ontario temperate forests in the foreseeable future.

Insufficient Chilling Effects Vary among Boreal Tree Species and Chilling Duration.

Insufficient chilling resulting from rising winter temperatures associated with climate warming has been an area of particular interest in boreal and temperate regions where a period of cool temperatures in fall and winter is required to break plant dormancy. In this study, we examined the budburst and growth of trembling aspen (Populus tremuloides Michx.), balsam poplar (Populus balsamifera L.), white birch (Betula papyrifera Marsh.), black spruce (Picea mariana (Mill.) B.S.P.), white spruce (Picea glauca (Moench) Voss), jack pine (Pinus banksiana Lamb.), and lodgepole pine (Pinus contorta Dougl. ex. Loud.) seedlings subjected to typical northern Ontario, Canada, spring conditions in climate chambers after different exposures to natural chilling. Results indicate that chilling requirements (cumulative weighted chilling hours) differed substantially among the seven species, ranging from 300 to 500 h for spruce seedlings to more than 1100 h for trembling aspen and lodgepole pine. Only spruce seedlings had fulfilled their chilling requirements before December 31, whereas the other species continued chilling well into March and April. Species with lower chilling requirements needed more heat accumulation for budburst and vice versa. Insufficient chilling delayed budburst but only extremely restricted chilling hours (<400) resulted in abnormal budburst and growth, including reduced needle and shoot expansion, early budburst in lower crowns, and erratic budburst on lower stems and roots. Effects, however, depended on both the species’ chilling requirements and the chilling–heat relationship. Among the seven tree species examined, trembling aspen is most likely to be affected by reduced chilling accumulation possible under future climate scenarios, followed by balsam poplar, white birch, lodgepole pine, and jack pine. Black and white spruce are least likely to be affected by changes in chilling hours.

Penyimpanan In Vitro Tanaman Obat Daun Dewa melalui Pertumbuhan Minimal

&lt;p class="p1"&gt;Daun dewa (&lt;em&gt;Gynura Procumbens&lt;/em&gt;) is a medicinal crop commonly used to remedy cancer, diabetes, and dermatitis. It has a bright prospect for future used. Plant preservations through tissue culture is done to anticipate an urgent need. An experiment was carried out to &lt;em&gt;in vitro &lt;/em&gt;preservation of Daun Dewa by the minimum growth and regeneration to examine viability of the culture after the preservation. Terminal shoots (±1 cm) were cultured on a 1/2 MS basic medium + paclobutrazol (0, 1, 2, 3, and 4 mg/l) or ABA (1, 2, and 5 mg/l). The trial was arranged in a, completely randomized with 10 replications. The results showed a three-month preservation of the culture on a medium containing ABA inhibited proliferation and expansion of the plant shoots. Increasing ABA concentrations up to 5 mg/l, according to the shoot-growth inhibition, resulted in the height of 0.6 cm. After three month preservation, the shoots were able to produce roots. After 12 month preservation, the optimum capacity of growth inhibition was shown on 1/2 MS medium + ABA (1, 3, and 5 mg/l). The application of paclobutrazol (1, 2, 3, and 4 mg/l) in the medium produced low multiplication level of shoots, the length of the shoots remains higher than those on 1/2 MS medium without paclobutrazol. Seven months after preservation, viability of the plants was still high when cultured on MS medium + 2 mg/l BA combined with paclobutrazol and ABA as previously given. In addition, the rooted culture could be directly acclimatized in the glasshouse. The lowest number of shoot and shortest shoot after 12 month preservation period was found on the medium containing 5 mg/l ABA and 4 mg/l paclobutrazol, this treatment produced two shoots of 4 cm long. The best medium for the explant regeneration after 7 month preservation was MS + 2 mg/l BA. The plant shoots produced roots directly after they were acclimatized in the glasshouse.&lt;/p&gt;

Phenotypic plasticity of leaves enhances water-stress tolerance and promotes hydraulic conductivity in a tall conifer.

Leaves respond to environmental signals and acclimate to local conditions until their ecological limits are reached. Understanding the relationships between anatomical variation in leaves and the availability of water and light improves our ability to predict ecosystem-level impacts of foliar response to climate change, as it expands our knowledge of tree physiology. We examined foliar anatomy and morphology of the largest plant species, Sequoiadendron giganteum, from leafy shoot samples collected throughout crowns of trees up to 95 m tall and assessed the functionality of within-crown variation with a novel drought/recovery experiment. We found phenotypic variation in response to water availability in 13 anatomical traits of Sequoiadendron leaves. Shoot expansion was constrained by the hydrostatic gradient of maximum water potential, while functional traits supporting succulence and toughness were associated with sites of peak hydraulic limitation. Water-stress tolerance in experimental shoots increased dramatically with height. We propose a heat-sink function for transfusion tissue and uncover a suite of traits suggesting rapid hydraulic throughput and flexibility in water-stress tolerance investments as strategies that help this montane species reach such enormous size. Responses to water stress alter the amount of carbon stored in foliage and the rate of the eventual release of carbon.

Chloride regulates leaf cell size and water relations in tobacco plants.

Chloride (Cl(-)) is a micronutrient that accumulates to macronutrient levels since it is normally available in nature and actively taken up by higher plants. Besides a role as an unspecific cell osmoticum, no clear biological roles have been explicitly associated with Cl(-) when accumulated to macronutrient concentrations. To address this question, the glycophyte tobacco (Nicotiana tabacum L. var. Habana) has been treated with a basal nutrient solution supplemented with one of three salt combinations containing the same cationic balance: Cl(-)-based (CL), nitrate-based (N), and sulphate+phosphate-based (SP) treatments. Under non-saline conditions (up to 5 mM Cl(-)) and no water limitation, Cl(-) specifically stimulated higher leaf cell size and led to a moderate increase of plant fresh and dry biomass mainly due to higher shoot expansion. When applied in the 1-5 mM range, Cl(-) played specific roles in regulating leaf osmotic potential and turgor, allowing plants to improve leaf water balance parameters. In addition, Cl(-) also altered water relations at the whole-plant level through reduction of plant transpiration. This was a consequence of a lower stomatal conductance, which resulted in lower water loss and greater photosynthetic and integrated water-use efficiency. In contrast to Cl(-), these effects were not observed for essential anionic macronutrients such as nitrate, sulphate, and phosphate. We propose that the abundant uptake and accumulation of Cl(-) responds to adaptive functions improving water homeostasis in higher plants.

Leaf development and expansion in tea [Camellia sinensis (L.) Kuntze] and their relationships with thermal time: a case study

Three field experiments were conducted to study the leaf and shoot expansion in tea [Camellia sinensis (L.) Kuntze] and their relationships with thermal time. The study site was Glen Alpine estate, Badulla, Sri Lanka located at an altitude of 1120 m above mean sea level (AMSL). The first experiment was carried out to develop a mathematical model to predict the area of an individual leaf and total leaf area of a harvestable shoot of widely grown tea cultivars namely, TRI 2025, TRI 2023, TRI 2043 and TRI 3035 in the Uva region. In the second experiment, the number of days required to initiate different leaves of a tea shoot of TRI 2025 was investigated. In the third experiment, the degree-days (thermal time) accumulated for producing different leaves and a harvestable tea shoot with three leaves of tea cultivar TRI 2025 were estimated. Stepwise regression resulted in a model with the product of leaf length and width to estimate the leaf area of a single tea leaf for all the evaluated cultivars with a high precision (R 2 =0.99). From the bud break, 128.5, 187.5, 234.5, 295.5 oC days were required to initiate the fish leaf, first normal leaf, second normal leaf and third normal leaf, respectively, of the tea cultivar TRI 2025. A harvestable tea shoot was produced after accumulating 392.5 oC days by the cultivar TRI 2025. Tropical Agricultural Research Vol. 25 (4): 250-259 (2014)

Evaluation of Groundnut Genotypes for Tolerance to Phosphorus Deficiency

Phosphorous (P) is one of the most deficient nutrients owing to its fixation and low mobility in acid soils. A total of 324 genotypes were screened in both P sufficient and insufficient conditions to evaluate the P uptake efficiency. Thirty-four responsive genotypes were evaluated in solution culture with two checks, ICGV 86590 and JL 24. The components of variability revealed high magnitude and highly heritable nature of the variation. Highly responsive genotypes to P insufficiency; ICG 14475, ICGV 92188, and M 68 were further tested for phosphorus uptake efficiency at 15, 30, and 45 days after sowing (DAS) along with checks in sand culture in pots. ICG 14475, ICGV 92188, and ICGV 86590 were found superior in both acquisition and utilization of phosphorus due to enhanced root production for P exploration and shoot expansion, respectively. JL 24 was poor in acquisition due to lack of response in root traits under P insufficiency.

Comparison of seasonal growth responses of Zostera marina transplants to determine the optimal transplant season for habitat restoration

Significant losses in seagrass coverage have been reported worldwide, and thus efforts are under way to restore disturbed seagrass habitats. Unfortunately, rates of seagrass restoration success through transplantation remain quite low, and inappropriate transplant times may be one cause of the low success rates. To determine suitable seasons for transplanting eelgrass, transplantation experiments were conducted seasonally. After each transplantation trial, shoot density, chlorophyll content, shoot morphology, and productivity of transplants and reference plants were monitored at 2–4-week intervals for approximately 3 months. All eelgrass transplants had disappeared by the end of the summer transplantation trial, whereas transplant density increased most rapidly in the fall transplantation. High water temperature in summer appeared to be a primary seasonal stress in eelgrass meadows, causing high transplant mortality. Results for shoot morphology, physiology, and growth of transplants indicated that those planted in summer suffered the most severe transplanting stress, whereas those planted in fall experienced the least stress. Accordingly, summer transplantation for eelgrass restoration should be avoided in areas where summer water temperatures are greater than 25°C. Because transplants planted in fall exhibited the highest expansion of shoots and suffered the least transplant stress, the optimal season for eelgrass transplantation is likely to be fall, just after the high water temperature period.

Rose bush leaf and internode expansion dynamics: analysis and development of a model capturing interplant variability.

Rose bush architecture, among other factors, such as plant health, determines plant visual quality. The commercial product is the individual plant and interplant variability may be high within a crop. Thus, both mean plant architecture and interplant variability should be studied. Expansion is an important feature of architecture, but it has been little studied at the level of individual organs in rose bushes. We investigated the expansion kinetics of primary shoot organs, to develop a model reproducing the organ expansion of real crops from non-destructive input variables. We took interplant variability in expansion kinetics and the model's ability to simulate this variability into account. Changes in leaflet and internode dimensions over thermal time were recorded for primary shoot expansion, on 83 plants from three crops grown in different climatic conditions and densities. An empirical model was developed, to reproduce organ expansion kinetics for individual plants of a real crop of rose bush primary shoots. Leaflet or internode length was simulated as a logistic function of thermal time. The model was evaluated by cross-validation. We found that differences in leaflet or internode expansion kinetics between phytomer positions and between plants at a given phytomer position were due mostly to large differences in time of organ expansion and expansion rate, rather than differences in expansion duration. Thus, in the model, the parameters linked to expansion duration were predicted by values common to all plants, whereas variability in final size and organ expansion time was captured by input data. The model accurately simulated leaflet and internode expansion for individual plants (RMSEP = 7.3 and 10.2% of final length, respectively). Thus, this study defines the measurements required to simulate expansion and provides the first model simulating organ expansion in rosebush to capture interplant variability.

Seasonal controls on net branch CO2 assimilation in sub-Arctic Mountain Birch (Betula pubescens ssp. czerepanovii (Orlova) Hamet-Ahti)

Forests at northern high latitudes are experiencing climate-induced changes in growth and productivity, but our knowledge on the underlying mechanisms driving seasonal CO2 fluxes in northern boreal trees comes almost exclusively from ecosystem-level studies on evergreen conifers. In this study, we measured growing season whole-branch CO2 exchange in a deciduous tree species of the tundra-taiga ecotone, Mountain Birch (Betula pubescens ssp. czerepanovii (Orlova) Hamet-Ahti), at two locations in northern Fennoscandia: Abisko (Sweden) and Kevo (Finland). We identified strong seasonal and environmental controls on both photosynthesis and respiration by analysing the parameters of light response curves. Branch-level photosynthetic parameters showed a delayed response to temperature, and, at Kevo, they were well described by sigmoid functions of the state of acclimation (S). Temperature acclimation was slower (time constant, τ=7days) for maximum photosynthesis (βbr) than for quantum efficiency (αbr) (τ=5days). High temperature-independent values of the respiration parameter (γbr) during leaf and shoot expansion were consistent with associated higher growth respiration rates. The ratio γbr/βbr was positively related to temperature, a result consistent with substrate-induced variations in leaf respiration rates at the branch level. Differences in stand structure and within-site variation in the active period of C uptake determined the spatiotemporal patterns in net assimilation amongst branches. Growing season CO2 uptake of individual branches on a leaf area basis did not show a significant relationship with total incident photosynthetically active radiation, and did not differ across sites, averaging ca. 640gCO2m−2.

Frost damage and its cascading negative effects on Aesculus glabra

Frost damage and re-foliation are seldom quantified for forest species, but are of ecological and evolutionary importance. This study of Aesculus glabra (Ohio buckeye) in a deciduous forest remnant in Illinois, USA, quantified frost damage to leaves and flowers after sub-freezing temperatures in April 2007. It also documented re-foliation and later growth, reproduction, and survival in 2007–2009 for the 355 study individuals of four life stages growing 0–200 m from the forest edge. Life stages differed in % leaf damage because of differences in phenology during the frost. Large saplings with fully expanded, immature leaves had higher % damage and lower % canopy fullness after re-foliation than smaller saplings with partially or fully mature leaves and canopy trees undergoing shoot expansion with folded leaflets. Percent damage increased for saplings closer to edges. Large saplings with heavier frost damage to leaves had partial re-foliation in deep shade, lower % canopy fullness, earlier senescence, a shorter growing season, and greater death of next year’s buds. By 2008, large saplings with greater damage in 2007 had more dead branches and lower % canopy fullness. By 2009, 11% of large saplings had died. In 2007, frost damaged no flowers, but final fruit crop size was negatively related to % leaf damage. Edge trees with total leaf damage aborted all fruits. The frost event differentially affected individuals in their length and time of growing season, energy budget, and, ultimately, reproduction, and survival. The population’s local-scale demography and spatial pattern also changed as large saplings died.

Aspen shoots are carbon autonomous during bud break

Current thinking holds that carbon autonomy of branches in trees is unlikely, particularly during bud break, when the new developing shoots require significant influx of carbon resources from more distant sources. Results from recent studies indicate that the impact of bud break on overall tree reserves might be small. In two studies the independence of flushing shoots from stored carbon reserves and the photosynthesis in developing new leaves and shoots of Populus tremuloides were explored. New developing shoots quickly became a positive carbon source and only a few days into flush, the photosynthetic system of the newly developing shoots was efficient enough to achieve positive carbon gain even at low light levels. Only 14% of the stored shoot reserves, without any mobilization from more distant reserves, were used during bud break and early shoot expansion. Without any underlying stress, shoots of deciduous trees appear to be carbon autonomous during bud break when demand on stored carbon should be the highest. The development of an efficient photosynthetic system in new shoots is critical in the recovery of carbon reserves in aspen. It minimizes the cost of bud break to the overall stored carbon reserves by optimizing the assimilation of carbon in the newly developed leaves, while eliminating the cost for mobilizing carbon reserves from more distant sources. This carbon autonomy of shoots has important implications for the whole tree carbon balance particularly to the non-photosynthetic tissues which functions solely depending on carbon export from the newly developing leaves and shoots.

Meristem Growth, Phenology, and Architecture in Chamaephytes of the Iberian Peninsula: Insights into a Largely Neglected Life Form

Protection of resting buds and timing of shoot development are crucial morphological traits of plants growing in a seasonal climate. For eight species of Iberian chamaephytes with contrasting morphology and ecology, we explored the different growth stages within the morphogenetic cycle of the shoot (including the initiation, morphogenesis and maturation of vegetative and reproductive structures), the seasonality of these growth stages and their relationship with the general climate of the species distribution area. We evaluated the implications of morphogenetic cycles on the phenology, architecture and distribution of each species, and tried to identify good descriptors of these cycles for their inclusion in databases of functional plant traits. The morphology, activity and growth of meristems and the expansion of shoots were assessed periodically by dissecting buds under stereomicroscope. Plant phenology was recorded monthly for a minimum of 13 months on 15 marked plants of six out of the eight study species. All species showed naked buds, with meristems protected by leaf primordia and surrounding young leaves. We identified five stages of growth that summarize the processes of organogenesis and expansion of primordia in study species. Depending on the temporal arrangement of these stages and the type of structures subtending renewal meristems, we identified two types of morphogenetic cycles in study species: naked buds formed on brachyblasts (short branches) that extend for a relatively long time by neoformation; and naked buds on little shoot primordia that remain concealed by part of subtending leaves and extend rapidly in spring (preformed growth) sometimes followed by a period of slow expansion by neoformation. These morphogenetic cycles seem to be related to the general climate where study species grow: species with brachyblasts grow preferentially in areas with dry summers and not very cold winters, while species with shoot primordia protected by leaf structures tend to grow in areas with cold winters and not very dry summers. Some traits like the type and size of buds, or the type of morphogenetic cycle are quite easy to measure and provide important ecological information. These traits are good candidates to be included in plant trait databases.

Physiological ecology of mycoheterotrophy

Physiological ecology of mycoheterotrophy