Differential springtime branch warming controls intra-crown nitrogen allocation and leaf photosynthetic traits in understory saplings of a temperate deciduous species.

Between-branch nitrogen competition is expected to be important during spring in temperate deciduous trees as nitrogen allocation would be higher in branches from earlier budburst than in those from later budburst. Such phenology-induced branch interaction would influence plant photosynthesis, but this has not been evaluated. Warming experiments were conducted on whole crowns (warmed trees; trunks and all branches of the same tree were warmed) or parts of the crowns (warmed branches with unwarmed control branches in the same tree), with unwarmed control trees, in saplings of the deciduous species Fraxinus lanuginosa. Spring leaf phenology and leaf photosynthetic traits were investigated to determine how the difference in temperature affects leaf phenology and photosynthetic traits. The timing of budburst was influenced by temperature-budburst was earlier in warmed trees and warmed branches than in control trees and control branches, but budburst timing did not differ between control trees and control branches or between warmed trees and warmed branches. In contrast, leaf traits were affected by the variation in phenology within crowns-nitrogen content and photosynthetic capacity were greater in the leaves of the warmed branches than in the control branches, but they did not differ between the leaves of warmed trees and control trees. Thus, branch warming altered the distribution of nitrogen between warmed and unwarmed branches as warmed branches developed faster, resulting in intracrown variation in leaf photosynthetic traits.

Genetic differentiation in the timing of budburst in Fagus crenata in relation to temperature and photoperiod.

Climate change is expected to influence plant productivity particularly through changes in the timing of budburst. Nonetheless, knowledge about the intraspecific variation of the timing of budburst and its relationship with climate is insufficient for most tree species. Based on the common garden experiments of Fagus crenata, we investigated the interrelationships between the day of budburst, cumulative degree-days (temperature sum), chilling duration, and photoperiod at the timing of budburst for the trees of different combinations of 11 sites of seed origin and seven experimental sites in Japan. We found that the relationship between the latitude of experimental sites and the timing of budburst differed for the trees of different latitudes of origins. The timing of budburst was earlier for the trees of more northern populations throughout the latitudes of experimental sites. Variation in the timing of budburst among the trees of different seed origins was smaller for more northern experimental sites. Such patterns were caused by directional changes in the relationships between temperature sum, chilling duration, and photoperiod among the trees of different origins: the asymptotes of the curvilinear relationship between chilling duration and temperature sum, chilling duration and photoperiod, and temperature sum and photoperiod, decreased for more northern populations. With the northward expansion of species distribution, the responses of budburst to climate probably changed genetically in such ways in this species. Our results suggest that intraspecific variations in the relationships between the timing of budburst and associated meteorological factors inevitably influence the overall pattern of the timing of budburst at the geographic scale, and the timing of budburst might deviate from predictions when intraspecific variations are not considered.

Relationships between the timing of budburst, plant traits, and distribution of 24 coexisting woody species in a warm-temperate forest in Japan.

PREMISE OF THE STUDY: Timing of budburst (DBB) may be related to the functional traits and distributions of woody species in temperate regions. Although many previous studies have investigated DBB in a number of temperate species, it has seldom been linked to multiple plant trait relationships. METHODS: DBB and plant traits were investigated for 24 woody species for 2 years in a warm-temperate secondary forest in Japan. Particular attention was paid to differences in trait relationships between coexisting deciduous and evergreen broad-leaved species. KEY RESULTS: DBB was correlated with plant traits in deciduous but not evergreen broad-leaved species; DBB was later for deciduous species with greater leaf mass, leaf area, vessel diameter, and leaf nitrogen content per unit mass. In addition, DBB was later for species with more northern distributions in deciduous and evergreen species. CONCLUSIONS: Clear differences in the trait relationships between deciduous and evergreen broad-leaved species might be caused by different selection pressures on DBB; selection is expected to be more severe in deciduous species. Overall, the continuous variable of vessel diameter might be used as a simple and effective trait to predict DBB of deciduous species regardless of wood anatomy; however, no such traits were detected as effective predictors of DBB in evergreen species at this study site. In addition, DBB was earlier for the species of more southern distributions, suggesting that such species benefit more from warming.

Inconsistent intraspecific pattern in leaf life span along nitrogen-supply gradient.

PREMISE OF THE STUDY: Leaf life span (LLS) has long been hypothesized to plastically increase with decreasing nitrogen (N) supply from soil to maximize N retention, carbon assimilation, and fitness; however, accumulating evidence shows no consistent trend. The apparent inconsistencies are explained by a recent model that assumes LLS has a hump-shaped quadratic response to the N-supply gradient. The available evidence mostly originates from comparisons of LLS at only two levels of N availability, and the hypothesis remains unanswered. METHODS: We investigated LLS of two asteraceous forbs (Adenocaulon himalaicum and Xanthium canadense) experimentally grown at eight levels of N supply, which covered a range of N supply in their natural habitats. We additionally conducted a literature search to retrieve studies reporting LLS response along an N-supply gradient. KEY RESULTS: The LLS of neither species showed a hump-shaped response along the N-supply gradient. Past studies examining the LLS of an aquatic forb and terrestrial shrubs and trees along the N-supply gradient (more than four levels of N supply) also refuted the hypothesis. CONCLUSIONS: The LLS of a single species exhibited neither an increase nor a hump-shaped response to decreased N supply in a variety of life forms. Comparisons at only a few N levels are misleading with regard to LLS response to N supply.

How is light interception efficiency related to shoot structure in tall canopy species?

Coexistence of multiple species is a fundamental aspect of plant and forest ecology. Although spatial arrangement of leaves within crowns is an important determinant of light interception and productivity, shoot structure varies considerably among coexisting canopy species. We investigated the relative importance of structural traits in determining the light availability of leaves (I) and light interception efficiency at the current-year shoot level (LIECS; the total light interception of leaves divided by shoot biomass) at the top of crowns of 11 canopy species in a cool-temperate forest in Japan. In accordance with Corner's rules, the total mass, stem mass, total mass of leaf laminae, individual leaf area, and stem cross-sectional area of current-year shoot were positively correlated with each other, and branching intensity (the number of current-year shoots per branch unit of 1-m length) was inversely correlated with these traits across species. In contrast, I was correlated not with these traits, but with leaf elevation angle (a L). Moreover, variation in LIECS across species was caused by variation in I (thus in a L). Thus, a L is a key parameter for the leaf light interception of canopy shoots in this cool-temperate forest. Differences in a L across species might be related to different physiological strategies that developed in the high light and water-limited environment of forest canopies. Small variation in the length of current-year shoots among species implies that variations in I and LIECS would be important for the coexistence of these canopy species.

Geographic variation in shoot traits and branching intensity in relation to leaf size in Fagus crenata: A common garden experiment.

PREMISE OF THE STUDY: Differences in leaf size are expected to be coordinated with various shoot traits and branching intensity because these relationships will influence light capture efficiency, water use, and biomechanics. Previous studies have mainly focused on interspecific patterns of these trait relationships, but not on intraspecific patterns at the geographic scale. We investigated intraspecific variation in shoot traits and branching intensity of Fagus crenata in Japan. METHODS: Allometric relationships between the traits of current-year shoots and branching intensity per branch unit of 1-m length on the main axis (BI) and its coordination with latitude were investigated using trees from 10 provenances in a common garden. KEY RESULTS: Individual trees originating from lower latitudes have smaller leaves with greater leaf mass per area and nitrogen content per area, greater Huber value (stem cross-sectional area per total leaf area [ATL]) of current-year shoots, and greater BI. Notably, the slope of the log-log relationship between BI and ATL was close to -1.0 across the trees from different source sites, implying that branching in this species occurs to control leaf area. CONCLUSIONS: Shoot traits and branching intensity were apparently coordinated with leaf size to control leaf area deployment in this species. Such patterns probably reflect differences in competition for hydraulic conductance among nearby shoots within crowns, as a consequence of different meteorological conditions across the source sites.

Leaf nitrogen distribution in relation to crown architecture in the tall canopy species, Fagus crenata.

The theory of optimal leaf N distribution predicts that the C gain of plants is maximized when the N content per unit area (N(area)) scales with light availability, but most previous studies have demonstrated that the N distribution is not proportional to light availability. In tall trees, the leaves are often clustered on twigs (leaf cluster) and not evenly distributed within the crowns. Thus, we hypothesized that the suboptimal N distribution is partly caused by the limited capacity to translocate N between leaf clusters, and consequently, the relationship between light and N(area) differs for leaves in different clusters. We investigated the light availability and N content of all individual leaves within several leaf clusters on tall trees of a deciduous canopy species Fagus crenata in Japan. We observed that the within-cluster leaf N distribution patterns differed from the between-cluster patterns and the slopes of the relationships between light and N(area) were lower within clusters than between clusters. According to the detailed analysis of the N distribution within leaf clusters, N(area) was greater for current-year shoots with greater light availability or a larger total leaf area. The latter pattern was probably caused by the greater sink strength of the current-year shoots with a larger leaf area. These N distribution patterns suggest that leaf clusters are fairly independent with respect to their N use, and the productivity of real F. crenata crowns may be less than optimal.

Differences between height- and light-dependent changes in shoot traits in five deciduous tree species.

The effects of tree height on shoot traits may in some cases differ in magnitude and direction from the effects of light. Nevertheless, general patterns of change in shoot traits in relation to variations in height and light have not so far been revealed. A comprehensive analysis of the differences between the effects of height and light on a range of leaf and shoot traits is important for the scaling of these traits to individual trees. We investigated the biomass allocation and structure of current-year shoots at the top of the crowns of five deciduous tree species in Japan. Height effect was investigated by comparing shoot traits among trees of different heights growing under a high light environment. The effects of light were examined by comparing saplings growing in high- and low-light environments. The effects of light were significant for most traits, while those of height were not significant for some traits. The magnitudes of the effects of light were larger than those of height for most traits related to biomass allocation. There was an extreme difference between the effects of height and light in the direction of change in the length of current-year shoots and in the number of standing leaves. The measures of both parameters increased with the increase in light, but decreased with the increase in tree height. Thus, the effects of height and light on diverse traits at the level of current-year shoots were not always similar. These results suggest that great care must be taken when scaling shoot traits from small trees to tall trees because the effects of height and light can be complex.

Geographic variation in shoot structure in association with fruit size in an evergreen woody species.

The generality of scaling relationships between multiple shoot traits, known as Corner's rules, has been considered to reflect the biomechanical limits to trees and tree organs among the species of different leaf sizes. Variation in fruit size within species would also be expected to affect shoot structure by changing the mechanical and hydraulic stresses caused by the mass and water requirement of fruits. We investigated the differences in shoot structure and their relationship with fruit size in Camellia japonica from 12 sites in a wide geographic range in Japan. This species is known to produce larger fruits with thicker pericarps in more southern populations because warmer climates induce more intensive arms race between the fruit size and the rostrum length of its obligate seed predator. We found that, in association with the change in fruit size, the diameter and mass of 1-year-old stems were negatively associated with latitude, but the total mass and area of 1-year-old leaves did not change with latitude. Consequently, the length of 1-year-old stems and the total mass and area of 1-year-old leaves at a given stem diameter were positively associated with latitude in the allometric relationships. In contrast, the allometric relationships between stem diameter and total mass of the 1-year-old shoot complex (the leaves, stems and fruits that were supported by a 1-year-old stem) did not differ across the trees of different latitudes. Thus, natural selection on fruit size is considered to influence the other traits of Corner's rules in C. japonica, but all of the traits of Corner's rules do not necessarily change in a similar manner across latitudinal gradients.

Effects of atmospheric CO2 concentration, irradiance, and soil nitrogen availability on leaf photosynthetic traits of Polygonum sachalinense around natural CO2 springs in northern Japan.

Long-term exposure to elevated CO2 concentration will affect the traits of wild plants in association with other environmental factors. We investigated multiple effects of atmospheric CO2 concentration, irradiance, and soil N availability on the leaf photosynthetic traits of a herbaceous species, Polygonum sachalinense, growing around natural CO2 springs in northern Japan. Atmospheric CO2 concentration and its interaction with irradiance and soil N availability affected several leaf traits. Leaf mass per unit area increased and N per mass decreased with increasing CO2 and irradiance. Leaf N per area increased with increasing soil N availability at higher CO2 concentrations. The photosynthetic rate under growth CO2 conditions increased with increasing irradiance and CO2, and with increasing soil N at higher CO2 concentrations. The maximal velocity of ribulose 1,5-bisphosphate carboxylation (V (cmax)) was affected by the interaction of CO2 and soil N, suggesting that down-regulation of photosynthesis at elevated CO2 was more evident at lower soil N availability. The ratio of the maximum rate of electron transport to V (cmax) (J (max)/V (cmax)) increased with increasing CO2, suggesting that the plants used N efficiently for photosynthesis at high CO2 concentrations by changes in N partitioning. To what extent elevated CO2 influenced plant traits depended on other environmental factors. As wild plants are subject to a wide range of light and nutrient availability, our results highlight the importance of these environmental factors when the effects of elevated CO2 on plants are evaluated.

The worldwide leaf economics spectrum.

Bringing together leaf trait data spanning 2,548 species and 175 sites we describe, for the first time at global scale, a universal spectrum of leaf economics consisting of key chemical, structural and physiological properties. The spectrum runs from quick to slow return on investments of nutrients and dry mass in leaves, and operates largely independently of growth form, plant functional type or biome. Categories along the spectrum would, in general, describe leaf economic variation at the global scale better than plant functional types, because functional types overlap substantially in their leaf traits. Overall, modulation of leaf traits and trait relationships by climate is surprisingly modest, although some striking and significant patterns can be seen. Reliable quantification of the leaf economics spectrum and its interaction with climate will prove valuable for modelling nutrient fluxes and vegetation boundaries under changing land-use and climate.

Ignoring non-English-language studies may bias ecological meta-analyses.

Meta-analysis plays a crucial role in syntheses of quantitative evidence in ecology and biodiversity conservation. The reliability of estimates in meta-analyses strongly depends on unbiased sampling of primary studies. Although earlier studies have explored potential biases in ecological meta-analyses, biases in reported statistical results and associated study characteristics published in different languages have never been tested in environmental sciences. We address this knowledge gap by systematically searching published meta-analyses and comparing effect-size estimates between English- and Japanese-language studies included in existing meta-analyses. Of the 40 published ecological meta-analysis articles authored by those affiliated to Japanese institutions, we find that three meta-analysis articles searched for studies in the two languages and involved sufficient numbers of English- and Japanese-language studies, resulting in four eligible meta-analyses (i.e., four meta-analyses conducted in the three meta-analysis articles). In two of the four, effect sizes differ significantly between the English- and Japanese-language studies included in the meta-analyses, causing considerable changes in overall mean effect sizes and even their direction when Japanese-language studies are excluded. The observed differences in effect sizes are likely attributable to systematic differences in reported statistical results and associated study characteristics, particularly taxa and ecosystems, between English- and Japanese-language studies. Despite being based on a small sample size, our findings suggest that ignoring non-English-language studies may bias outcomes of ecological meta-analyses, due to systematic differences in study characteristics and effect-size estimates between English- and non-English languages. We provide a list of actions that meta-analysts could take in the future to reduce the risk of language bias.

La méta­analyse joue un rôle essentiel dans les synthèses de preuves quantitatives en écologie et en conservation de la biodiversité. La fiabilité des estimations dans les méta­analyses dépend fortement d'un échantillonnage non biaisé des études primaires. Bien que des études antérieures aient examiné les biais potentiels dans les méta­analyses écologiques, les biais n'ont jamais été mis à l'épreuve dans les sciences de l'environnement lors de publications dans différentes langues de résultats statistiques enregistrés et de caractéristiques des études associées. Nous abordons cette lacune dans les connaissances en recherchant de manière systématique des méta­analyses publiées et en comparant les estimations d'ampleur de l'effet entre des études en anglais et en japonais figurant dans les méta­analyses existantes. Sur 40 articles publiés de méta­analyse écologique dont les auteurs sont affiliés à des institutions japonaises, nous trouvons que trois articles de méta­analyse ont recherché des études dans les deux langues et ont mis en jeu des nombres suffisants d'études en anglais et en japonais, avec pour résultat quatre méta­analyses admissibles (c.­à­d. quatre méta­analyses effectuées dans les trois articles de méta­analyse). Dans deux de ces quatre cas, les ampleurs de l'effet diffèrent de façon significative entre les études en japonais et en anglais comprises dans les méta­analyses, ce qui provoque des changements considérables dans les ampleurs moyennes globales de l'effet et même dans leur direction lorsque les études en japonais sont exclues. On peut probablement attribuer les différences observées dans les ampleurs de l'effet entre les études en japonais et en anglais, en particulier en ce qui concerne les taxons et les écosystèmes, aux différences systématiques dans les résultats statistiques enregistrés, de même que dans les caractéristiques des études associées. Bien que basés sur un échantillon de petite taille, nos résultats suggèrent que le fait d'ignorer les études non anglophones peut biaiser les résultats de méta­analyses écologiques en raison des différences systématiques dans les caractéristiques d'étude et les estimations d'ampleur de l'effet entre langue anglaise et langues non anglophones. Nous proposons une liste de mesures qui pourraient être adoptées à l'avenir dans les méta­analyses pour réduire le risque de biais linguistique.

A metanálise desempenha um papel crucial na síntese de evidências quantitativas na ecologia e conservação da biodiversidade. A confiabilidade das estimativas nas metanálises depende fortemente da amostragem imparcial de estudos primários. Embora estudos anteriores tenham explorado possíveis vieses em metanálises ecológicas, os vieses nos resultados estatísticos relatados e características de estudos associados publicados em diferentes idiomas nunca foram testados em ciências ambientais. Abordamos essa lacuna de conhecimento pesquisando sistematicamente metanálises publicadas e comparando estimativas de tamanho de efeito entre os estudos em inglês e japonês incluídos nas metanálises existentes. Dos 40 artigos de metanálise ecológica publicados por autores filiados a instituições japonesas, descobrimos que três artigos de metanálise pesquisaram estudos nos dois idiomas e envolveram um número suficiente de estudos em inglês e japonês, resultando em quatro metanálises elegíveis (ou seja, quatro metanálises realizadas nos três artigos de metanálise). Em duas das quatro metanálises, os tamanhos de efeito diferem significativamente entre os estudos em inglês e japonês incluídos nas metanálises, causando mudanças consideráveis nos tamanhos de efeito médios em geral e até mesmo na sua direção quando os estudos em japonês são excluídos. As diferenças observadas nos tamanhos de efeito provavelmente são atribuíveis a diferenças sistemáticas nos resultados estatísticos relatados, bem como às características de estudos associados, particularmente táxons e ecossistemas, entre estudos em inglês e japonês. Embora baseados em um pequeno tamanho amostral, nossos resultados sugerem que ignorar estudos que não sejam em inglês pode influenciar os resultados de metanálises ecológicas, devido a diferenças sistemáticas nas características dos estudos e estimativas de tamanho de efeito entre o idioma inglês e o não­inglês. Fornecemos uma lista de medidas que metanalistas podem adotar no futuro para reduzir o risco de viés de idioma.

El meta­análisis juega un papel crucial en la síntesis de evidencia cuantitativa en ecología y conservación de la biodiversidad. La fiabilidad de las estimaciones en los meta­análisis depende en gran medida del muestreo imparcial de los estudios primarios. A pesar de que estudios previos han explorado posibles sesgos en meta­análisis ecológicos, sesgos en resultados estadísticos y características asociadas al estudio publicados en diferentes idiomas nunca han sido comprobados en ciencias ambientales. Abordamos esta brecha de conocimiento buscando sistemáticamente los meta­análisis publicados y comparando las estimaciones del tamaño del efecto entre los estudios en inglés y japonés incluidos en los meta­análisis existentes. De los 40 artículos de meta­análisis ecológicos publicados por aquellos afiliados a instituciones japonesas, encontramos que tres artículos de meta­análisis buscaron estudios en dos idiomas e involucraron un número suficiente de estudios en inglés y japonés, lo que resultó en cuatro meta­análisis elegibles (i.e., cuatro meta­análisis realizados en tres artículos de meta­análisis). En dos de los cuatro, los tamaños de los efectos difieren significativamente entre los estudios en inglés y japonés incluidos en los meta­análisis, lo que provoca cambios considerables en los tamaños de efectos medios generales e incluso su dirección cuando se excluyen los estudios en japonés. Las diferencias observadas en los tamaños de los efectos son probablemente atribuibles a las diferencias sistemáticas en los resultados estadísticos informados, así como a las características de los estudios asociados, particularmente los taxones y los ecosistemas, entre los estudios en inglés y japonés. A pesar de estar basados ​​en un tamaño de muestra pequeño, nuestros hallazgos sugieren que ignorar los estudios que no están en inglés puede sesgar los resultados de los meta­análisis ecológicos, debido a las diferencias sistemáticas en las características del estudio y a las estimaciones del tamaño del efecto entre el idioma inglés y el no inglés. Proporcionamos una lista de acciones que los meta­analistas podrían tomar en el futuro para reducir el riesgo de sesgo lingüístico.

Intraspecific differences in spring leaf phenology in relation to tree size in temperate deciduous trees.

Spring leaf phenology strongly influences plant productivity in temperate deciduous forests. Many studies have detected earlier budburst and leaf maturation in smaller trees within species, and have discussed the adaptive significance of increasing carbon gain before canopy closure in small trees. However, some previous studies have found the opposite pattern, and the physiological and environmental bases for this discrepancy are incompletely understood. We investigated the spring leaf phenology of 11 deciduous species in a cool-temperate forest in Japan for 2 years with different amounts of snowfall, and also gathered data on the day of budburst from multiple studies to assess whether and how the timing of budburst is related to tree size, phylogeny, temperature and annual snowfall of study sites. We found that differences in the timing of budburst and leaf maturation between saplings (<1 m height) and short trees (1-10 m height) are larger than those between short trees and tall trees (>10 m height), resulting in non-linear relationships between timing and height in most species. Cumulative degree-days to the day of budburst were smaller in saplings than in tall trees, probably because saplings are selected to outcompete the other individuals/species to become established. Moreover, phylogenetic relatedness did not explain the difference in spring leaf phenology between saplings and tall trees in the literature survey. In addition, our literature survey showed that budburst occurred earlier in saplings of most species in sites with less snowfall, whereas budburst occurred earlier in tall trees at sites with heavy snowfall. These results suggest that the opposite patterns found in some studies may be due to (i) differences in the target size, as saplings show larger phenological discrepancies than short and tall trees, and (ii) the microclimate experienced by the tree, as sites with heavy snow show delayed sapling phenology.

Effective use of high CO2 efflux at the soil surface in a tropical understory plant.

Many terrestrial plants are C3 plants that evolved in the Mesozoic Era when atmospheric CO2 concentrations ([CO2]) were high. Given current conditions, C3 plants can no longer benefit from high ambient [CO2]. Kaempferia marginata Carey is a unique understory ginger plant in the tropical dry forests of Thailand. The plant has two large flat leaves that spread on the soil surface. We found a large difference in [CO2] between the partly closed space between the soil surface and the leaves (638 µmol mol(-1)) and the atmosphere at 20 cm above ground level (412 µmol mol(-1)). This finding indicates that the plants capture CO2 efflux from the soil. Almost all of the stomata are located on the abaxial leaf surface. When ambient air [CO2] was experimentally increased from 400 to 600 µmol mol(-1), net photosynthetic rates increased by 45 to 48% under near light-saturated conditions. No significant increase was observed under low light conditions. These data demonstrate that the unique leaf structure enhances carbon gain by trapping soil CO2 efflux at stomatal sites under relatively high light conditions, suggesting that ambient air [CO2] can serve as an important selective agent for terrestrial C3 plants.

Changes in shoot allometry with increasing tree height in a tropical canopy species, Elateriospermum tapos.

Allometry of shoot extension units (hereafter termed "current shoots") was analyzed in a Malaysian canopy species, Elateriospermum tapos Bl. (Euphorbiaceae). Changes in current shoot allometry with increasing tree height were related to growth and maintenance of tree crowns. Total biomass, biomass allocation ratio of non-photosynthetic to photosynthetic organs, and wood density of current shoots were unrelated to tree height. However, shoot structure changed with tree height. Compared with short trees, tall trees produced current shoots of the same mass but with thicker and shorter stems. Current shoots with thin and long stems enhanced height growth in short trees, whereas in tall trees, thick and short current shoots may reduce mechanical and hydraulic stresses. Furthermore, compared with short trees, tall trees produced current shoots with more leaves of lower dry mass, smaller area, and smaller specific leaf area (SLA). Short trees adapted to low light flux density by reducing mutual shading with large leaves having a large SLA. In contrast, tall trees reduced mutual shading within a shoot by producing more small leaves in distal than in proximal parts of the shoot stem. The production of a large number of small leaves promoted light penetration into the dense crowns of tall trees. All of these characteristics suggest that the change in current shoot structure with increasing tree height is adaptive in E. tapos, enabling short trees to maximize height growth and tall trees to maximize light capture.

Crown development in a pioneer tree, Rhus trichocarpa, in relation to the structure and growth of individual branches.

Based on an allometric reconstruction, the structure and biomass-allocation patterns of branches and current-year shoots were investigated in branches of various heights in the pioneer tree Rhus trichocarpa, to evaluate how crown development is achieved and limited in association with height. Path analysis was conducted to explore the effects of light availability, basal height and size of individual branches on branch structure and growth. Branch angle was affected by basal height, whereas branch mass was influenced primarily by light availability. This result suggests that branch structure is strongly constrained by basal height, and that trees mediate such constraints under different light environments. Previous-year leaf area and light availability showed positive effects on current-year stem mass. In contrast, branch basal height and mass negatively affected current-year stem mass. Moreover, the length of stems of a given diameter decreased with increasing branch height. Therefore the cost of biomass investment for a unit growth in length is greater for branches of larger size and at upper positions. Vertical growth rate in length decreased with increasing height. Height-dependent changes in stem allometry and angle influenced the reduction in vertical growth rate to a similar degree.

Within-crown variation in the timing of leaf emergence and fall of Malaysian trees in association with crown development patterns.

In aseasonal tropics, timing of leaf emergence and leaf fall may differ between the shoots of different crown parts within a tree. This is important for the efficient development of crowns because leaves should be produced as soon as enough carbohydrates are accumulated. This hypothesis was tested by investigating leaf demography over a 44-mo period for 17 Malaysian trees and comparing the timings of leaf emergence and fall between the upper and lower crowns. The timings of leaf emergence were synchronized between the upper and lower crowns, but those of leaf fall were less synchronized in most trees. Greater rates of leaf production in the upper than in the lower crowns were attributable to the differences in the number of leaves that emerged per leaf emergence event, rather than differences in frequency of leaf emergence per year. Timings of leaf emergence and leaf fall were mainly simultaneous in the upper and lower crowns, but unsynchronized leaf production and leaf fall also occurred. Such limited plasticity of leaf demography within crowns may be the result of physiological integration of branches or the compromise between the advantages of satiating herbivores and effective crown development in the trees of aseasonal tropics.

Assessing the generality of global leaf trait relationships.

Global-scale quantification of relationships between plant traits gives insight into the evolution of the world's vegetation, and is crucial for parameterizing vegetation-climate models. A database was compiled, comprising data for hundreds to thousands of species for the core 'leaf economics' traits leaf lifespan, leaf mass per area, photosynthetic capacity, dark respiration, and leaf nitrogen and phosphorus concentrations, as well as leaf potassium, photosynthetic N-use efficiency (PNUE), and leaf N : P ratio. While mean trait values differed between plant functional types, the range found within groups was often larger than differences among them. Future vegetation-climate models could incorporate this knowledge. The core leaf traits were intercorrelated, both globally and within plant functional types, forming a 'leaf economics spectrum'. While these relationships are very general, they are not universal, as significant heterogeneity exists between relationships fitted to individual sites. Much, but not all, heterogeneity can be explained by variation in sample size alone. PNUE can also be considered as part of this trait spectrum, whereas leaf K and N : P ratios are only loosely related.

Branch architecture, light interception and crown development in saplings of a plagiotropically branching tropical tree, Polyalthia jenkinsii (Annonaceae).

To investigate crown development patterns, branch architecture, branch-level light interception, and leaf and branch dynamics were studied in saplings of a plagiotropically branching tree species, Polyalthia jenkinsii Hk. f. & Thoms. (Annonaceae) in a Malaysian rain forest. Lengths of branches and parts of the branches lacking leaves ('bare' branches) were smaller in upper branches than in lower branches within crowns, whereas lengths of 'leafy' parts and the number of leaves per branch were larger in intermediate than in upper and lower branches. Maximum diffuse light absorption (DLA) of individual leaves was not related to sapling height or branch position within crowns, whereas minimum DLA was lower in tall saplings. Accordingly, branch-level light interception was higher in intermediate than in upper and lower branches. The leaf production rate was higher and leaf loss rate was smaller in upper than in intermediate and lower branches. Moreover, the branch production rate of new first-order branches was larger in the upper crowns. Thus, leaf and branch dynamics do not correspond to branch-level light interception in the different canopy zones. As a result of architectural constraints, branches at different vertical positions experience predictable light microenvironments in plagiotropic species. Accordingly, this pattern of carbon allocation among branches might be particularly important for growth and crown development in plagiotropic species.

Changes in crown development patterns and current-year shoot structure with light environment and tree height in Fagus crenata (Fagaceae).

The relative effects of light and tree height on the architecture of leader crowns (i.e., the leading section of the main trunk, 100 cm in length) and current-year shoots for a canopy species, Fagus crenata, occupying both the ridge top and the valley bottom in a cool-temperate forest in Japan were investigated. For leader crowns, the number of current-year shoots and leaves increased with increasing tree height, whereas the mean length of current-year shoots increased with increasing relative photon flux density (PFD). The leader crown area decreased, and the depth and leaf area index of leader crowns increased, with increasing relative PFD. The mass of current-year shoots increased with relative PFD. However, this total mass was allocated differently between stems and leaves depending on tree height, such that the relative allocation to stems increased with increasing tree height. Furthermore, stem structures within current-year shoots also changed with height, such that taller trees produced thicker and shorter stems of the same volume. In contrast, leaf structure and leaf biomass allocations changed with relative PFD. Specific leaf area decreased with increasing relative PFD. In addition, leaf number increased more rapidly with increasing individual leaf mass for trees exposed to greater relative PFD. Consequently, the total leaf area supported by a stem of a given diameter decreased with increasing tree height and relative PFD. Thus, the architecture of leader crowns and current-year shoots were related differently to light and tree height, which are considered important for efficient light capture and the growth of small and tall trees in different environments.