Foliar Morphology Research Articles

Are Chilean coastal forests pre‐Pleistocene relicts? Evidence from foliar physiognomy, palaeoclimate, and phytogeography

AbstractAim We ask whether contemporary forests of the Chilean Coastal Range can be considered to be direct and conservative descendants of pre‐Pleistocene palaeofloras that occurred in southern South America from the Palaeogene to early Neogene periods (65–10 Ma), maintaining foliar physiognomies that do not match their present‐day climate. We also identify the most likely ancestors of present‐day coastal forests.Location Coastal Range of south‐central Chile (33–40° S).Methods We compared leaf morphology between five representative modern floras from mid‐latitude forests of the Chilean Coastal Range, and 14 Palaeogene–early Neogene palaeofloras from southern South America. We also compared the composition of biogeographical elements (defined by the modern distribution of plant genera) between fossil and present‐day assemblages. Palaeoclimatic reconstructions were based on a canonical correspondence analysis between leaf morphology of modern assemblages and eight climatic variables, and tested by a Monte Carlo permutation test. We compared the relative positions of fossil and modern floras on the environmental vector space defined by Canoco, and on axes defined by instrumental and estimated temperature and precipitation data.Results According to foliar characters, Palaeogene palaeofloras were strikingly divergent from present‐day coastal forests of central Chile. In contrast, two extant forest floras of the Chilean Coastal Range have a foliar morphology that resembles some late Eocene to early Miocene mixed palaeofloras, at least 23 Myr older. These two modern sites are representative of an area of the Coastal Range (36–37° S) that has been highlighted for its relictual character. None of the 14 fossil floras corresponded exactly to the modern composition of phytogeographic elements, although correspondence analyses showed that mixed and Neogene subtropical fossil floras were compositionally close to the extant woody floras of coastal forests in central Chile.Main Conclusions Contemporary forests of the Chilean Coastal Range exhibit strong physiognomic resemblance to the mixed palaeofloras from 33°57′ to 41°15′ S, which may be the closest ancestor of the deciduous and endemic‐rich Maulino forest, presently restricted to coastal areas between 36° and 38° S. In turn, the Neogene subtropical palaeoflora that occurred in the Proto‐Andean foothills of central Chile is the likely predecessor of Mediterranean‐type sclerophyllous forests of central Chile (32–33° S). Despite foliar resemblance between the late pre‐Pleistocene and extant forest floras, our palaeoclimatic reconstructions suggest that modern assemblages exist under climatic conditions that do not match their foliar physiognomy. We attribute this convergence in foliar morphology to the ‘evolutionary inertia’ of surviving lineages, favoured by the buffering effect of the coastal environment on climatic variability.

Leaf hydraulic capacity in ferns, conifers and angiosperms: impacts on photosynthetic maxima

* The hydraulic plumbing of vascular plant leaves varies considerably between major plant groups both in the spatial organization of veins, as well as their anatomical structure. * Five conifers, three ferns and 12 angiosperm trees were selected from tropical and temperate forests to investigate whether the profound differences in foliar morphology of these groups lead to correspondingly profound differences in leaf hydraulic efficiency. * We found that angiosperm leaves spanned a range of leaf hydraulic conductance from 3.9 to 36 mmol m2 s-1 MPa-1, whereas ferns (5.9-11.4 mmol m-2 s-1 MPa-1) and conifers (1.6-9.0 mmol m-2 s-1 MPa-1) were uniformly less conductive to liquid water. Leaf hydraulic conductance (Kleaf) correlated strongly with stomatal conductance indicating an internal leaf-level regulation of liquid and vapour conductances. Photosynthetic capacity also increased with Kleaf, however, it became saturated at values of Kleaf over 20 mmol m-2 s-1 MPa-1. * The data suggest that vessels in the leaves of the angiosperms studied provide them with the flexibility to produce highly conductive leaves with correspondingly high photosynthetic capacities relative to tracheid-bearing species.

Caracteres diagnósticos foliares en táxones ibéricos de <i>Isoetes L.</i> (Isoetaceae, Pteridophyta)

This is a comparative study of foliar morphology of the species of Isoetes L. growing in the Iberian Peninsula. The taxa included are /. durieui and /. histrix (terrestrial), /. setaceum, and /. velatum subsp. Velatum (amphibious), and /. brochonii, I. echinosporum, I. x hickeyi, I. lacustre, I. longissimum and /. velatum subsp. Asturicense (aquatic). Material of an undescribed amphibious tetraploid taxon related to /. velatum was also included in this study and referred as Isoetes sp. until proper description. Several Iberian collections, together with European and American specimens of some of the taxa were analyzed. Selected diagnostic characters of the microphylls are: cuticular ornamentation (striae, ridges and warts), cuticular flanges, epidermal patterns, stomata distribution and dimensions, foliar transverse sections outline, degree of development of the mesophyll, presence or absence, and distribution of the mechanical tissues (collenchyma), diaphragms, and presence or absence and type of intercellular pectic protuberances. All characters are stable, and do not vary with the age of the plants or the microphylls. Cuticular striae, ridges and warts, as well as stomata develop early in plantlets. Stomata present in the microphylls of two aquatic taxa ( /. longissimum, I. velatum subsp. asturicense ) suggest that their absence is not entirely due to influence of aquatic environment. Collenchyma occurs, also, in species growing in different habitats. Restored herbarium material proved to be as useful as fresh or fixed material, an important advantage in the case of Isoetes species, many of which grow in vulnerable areas or are known only through herbarium specimens due to destruction of their pristine habitats.

Maravilha: uma nova seleção de tangerina 'Sunki'

Apesar das variações somáticas identificadas em pomares comerciais e em coleções de variedades serem, geralmente, desfavoráveis, apresentando baixa produtividade de frutos, morfologia foliar atípica ou frutos anormais, inúmeras mutações espontâneas de inquestionável valor têm sido identificadas, haja vista que a grande maioria das variedades cítricas comerciais, copas e porta-enxertos surgiu como decorrência de algum tipo de mutação natural. O presente trabalho diz respeito à exploração dessa importante via de obtenção de novos clones e variedades, fazendo parte de ações do Programa de Melhoramento Genético de Citros da Embrapa Mandioca e Fruticultura. Refere-se a uma nova seleção de tangerina 'Sunki', denominada 'Maravilha', identificada dentro de um grupo de seedlings nucelares da seleção 'da Flórida'. Foram realizadas comparações da 'Sunki Maravilha' com outras três seleções dessa tangerina, 'Comum', 'da Flórida' e 'Tropical', compreendendo os caracteres: número médio de sementes por fruto, número médio de embriões por semente, intervalo de variação do número de embriões por semente, porcentagem de poliembrionia e tamanho de embrião. Comparações foram efetuadas, também, com outros importantes porta-enxertos comerciais, limões 'Cravo' e 'Volkameriano' e tangerina 'Cleópatra', relativas a caracteres relacionados à germinação de sementes e ao vigor de seedlings (altura e número de folhas verdadeiras). Os resultados obtidos permitem indicar a seleção 'Sunki Maravilha' como alternativa de uso em programas de diversificação de porta-enxertos, nas condições em que esta tangerina apresenta boa adaptação, principalmente em função de seu relativamente elevado número médio de sementes por fruto (7,7), previsível uniformidade de seedlings, esta decorrente da elevada porcentagem de poliembrionia (100%), boa germinação de sementes e vigor de seedlings, além de provável resistência à gomose de Phytophthora spp.

In vitro rooting of juvenile and mature Acacia mangium microcuttings with reference to leaf morphology as a phase change marker

Rooting capacity of microshoots derived from a mature clone of Acacia mangium Willd. and from its juvenile progeny was compared in different in vitro conditions and in relation to leaf morphology as a phase change marker. Rooting capacity of the mature clone appeared to depend a lot on rooting medium composition, in contrast to the juvenile plant material. On a SH/3 derived medium with 4 µM IAA, the rooting rates varied significantly according to microshoot morphology and light regime starting from day 14. Maintaining the microshoots for 3 weeks in total darkness prior to transfer to the standard 16-h photoperiod increased the rooting rates overall. Mature-like microshoots of juvenile origin rooted in much lower proportions than the juvenile-like ones under the 16-h photoperiod, whereas no difference in rooting rates between the two morphological types was observed after 3 weeks in total darkness. The results were totally opposite for the mature clone for which 3 weeks in darkness, in contrast to the 16-h photoperiod, induced morphology-related differences in rooting rates with higher scores for the juvenile type. This study shows that under certain conditions, A. mangium microshoots from mature origin but with juvenile morphology can root in vitro with similar success rates (70%) to microshoots from juvenile plant material. However, the inconsistencies observed between the two age classes of microshoots in relation to photoperiod refute the use of foliar morphology as a reliable marker of rooting ability in A. mangium, although these two traits are classically referred to as phase change indicators.

Vertical gradients and tree-to-tree variation in shoot morphology and foliar nitrogen in an old-growth Pinus strobus stand

Acclimation to ambient light has been assumed to be the principal cause of vertical gradients in leaf nitrogen, foliar morphology, and related traits in forest canopies. We examined the relative role of crown exposure, damage, and reproduction as correlates of vertical gradients in shoot and needle morphology, anatomy, and chemistry in a ~120-year-old stand of Pinus strobus L. (eastern white pine) in central Ontario. Internodes at the top of trees were longer, wider, and produced more fascicles, but had lower fascicle survivorship than lower-canopy shoots. Needles on upper-canopy shoots also had higher allocation to resin ducts than mid- or lower-canopy needles, contained less nitrogen on a mass basis, and showed a higher leaf mass per area, C/N ratio, and chlorophyll a/b ratio. Tree-to-tree variation among the 26 trees measured traits was high, owing, in part, to differences in crown damage and reproductive status. Crown damage was associated with reduced leaf mass per area and other traits associated with shade acclimation, while high cone production was associated with reduced leaf nitrogen and chlorophyll in the upper canopy. Our results suggest that factors other than light acclimation play an important role in determining vertical gradients in foliar morphology, nitrogen, and leaf production in forest canopies.

Phylogenetic studies of Ophioglossaceae: evidence from rbcL and trnL-F plastid DNA sequences and morphology

Ophioglossaceae are a putatively ancient lineage of ferns in which the aerial portion of the plant is composed of a single leaf. The simplicity of foliar morphology has limited the number of characters available for constructing classifications and contributed to taxonomic difficulties at nearly every level of classification within the family. Analysis of plastid DNA rbcL sequences from 36 species representing the diversity of Ophioglossaceae supported the monophyly of the family. Intrafamilial relationships were examined using rbcL and trnL-F plastid DNA sequences and morphological data. Individual and combined analyses of the three data sets revealed two main clades within the family, here termed ophioglossoid and botrychioid. In the botrychioid clade, Helminthostachys was sister to a broadly defined Botrychium, within which Botrychium in the narrow sense of some authors and Sceptridium were sister. Botrypus was paraphyletic, with Botrypus virginianus sister to Botrychium plus Sceptridium, and with Botrypus strictus sister to all other botrychioid species except Helminthostachys. In the ophioglossoid clade, Ophioglossum in the narrow sense was sister to Cheiroglossa plus Ophioderma, but relationships within Ophioglossum were not well supported.

Somatic hybridisation for improvement of citrus rootstock: production of five new combinations with potential for improved disease resistance

The development of biotechnological tools such as protoplast fusion has provided a means of bypassing natural barriers related to reproductive biology of citrus found in conventional breeding systems. We report the production of 4 interspecific somatic hybrids, Cleopatra mandarin + Volkamer lemon, Ruby Blood sweet orange + Volkamer lemon, Rohde Red Valencia sweet orange + Volkamer lemon, and Rangpur lime + Sunki mandarin, and 1 intergeneric somatic hybrid, Valencia sweet orange + Fortunella obovata (Tanaka), which may be included and evaluated in rootstock improvement programs. Protoplasts were isolated from embryogenic calli and seedling leaves, and chemically fused with polyethylene glycol. Plants were regenerated via somatic embryogenesis and somatic hybridisation was confirmed by foliar morphology, cytological and DNA (RAPD) analyses. Somatic hybrids may combine required rootstock characteristics such as tolerance to citrus blight, tristeza virus, and Phytophthora, and have potential for control of tree size due to polyploidy.

Foliar morphology and canopy nitrogen as predictors of light-use efficiency in terrestrial vegetation

The net primary productivity (NPP) of a plant community is often positively and linearly related to the amount of photosynthetically active radiation absorbed by its canopy (APAR). The slope of this relationship is governed by the efficiency ( ε) of APAR use in biomass production (NPP=APAR× ε). This intuitive model offers a promising means of generating large-scale NPP estimates, but its utility is compromised by our inability to explain considerable differences in ε across species, functional groups, and environments. Using data from the literature, we examined the possibility that variation in ε was governed largely by two chemical and morphological characteristics of the vegetation, canopy nitrogen content ( N canopy) and the canopy average for leaf mass per unit area ( M area). Specifically, we hypothesized that ε was positively related to the quotient of N canopy (adjusted for the fraction of incident PAR absorbed by the canopy, f PAR) and M area. This ε index accounts for the dependence of light utilization on the quantity of photosynthetic “machinery” ( N canopy) and its inherent efficiency, which is inversely related to M area. Across a wide array of C 3 species, functional groups and environments, ε (based on aboveground NPP) was strongly and positively related to [ N canopy/ f PAR]/ M area ( r 2=0.85, P<0.0001). Adoption of the index as a basis for estimating ε could improve APAR-based predictions of terrestrial NPP, agricultural crop yield and vegetation responses to global change.

Age- and size-related trends in woody plant shoot development: regulatory pathways and evidence for genetic control.

Woody plants exhibit significant and predictable patterns of change in morphology and physiology as they become older and larger. Four models of potential pathways controlling these changes are presented: a stimulus-response model in which fully developed organs respond to changes in environment (defined here as everything external to the organ); an extrinsic model in which the attributes of developing organs are determined by environmental factors; an intrinsic model in which changes are a result of programmed changes in gene expression; and an extrinsic-intrinsic model in which changes in gene expression are induced by environmental factors. We review evidence that a genetic component is involved in controlling age- and size-related changes in foliar morphology and physiology and discuss the possibility of complex interactions among model pathways.

Age-related changes in foliar morphology and physiology in red spruce and their influence on declining photosynthetic rates and productivity with tree age.

The contribution of changes in meristem behavior to age-related decline in forest productivity is poorly understood. We studied age-related trends in needle morphology and gas exchange in a population of red spruce (Picea rubens Sarg.) growing in a multi-cohort stand where trees ranged from first-year germinants to trees over 150 years old, as well as in grafted scions from these trees. In the field study, age-related trends in foliar morphology were determined in six cohorts ranging in age from 2 to 120 years, and differences in gas exchange characteristics were compared between 60- and 120-year age classes. In a common-rootstock study, scions from trees representing 20-, 60-, and 120-year cohorts were grafted onto juvenile rootstock and maintained for three growing seasons, after which morphological and physiological foliar attributes were evaluated. The field study revealed significant age-related trends in foliar morphology, including decreasing specific leaf area, and increasing needle width, projected area, and width/length ratio. Similar trends were apparent in foliage from the grafted scions. Both in situ foliage and shoots of grafted scions from the oldest cohort showed significantly lower photosynthetic rates than their counterparts from younger trees; however, differences in stomatal conductance and internal CO(2) concentrations were not significant. These results suggest that: (1) foliage of red spruce exhibits age-related trends in both morphology and physiology; (2) age-related decreases in photosynthetic rates contribute to declining productivity in old red spruce; (3) declines in photosynthetic rates result from nonstomatal limitations; and (4) age-related changes in morphology and physiology are inherent in meristems and persist for at least 3 years in scions grafted to juvenile rootstock.

Spectral reflectance of Picea rubens (Pinaceae) and Abies balsamea (Pinaceae) needles along an elevational gradient, Mt. Moosilauke, New Hampshire, USA

Relationships among elevation, foliar morphology, spectral reflectance, and chlorophyll fluorescence of two co-occurring montane conifers, red spruce (Picea rubens Sarg.) and balsam fir (Abies balsamea [L.] Mill.), were investigated along two transects from 460 to 1460 m on Mt. Moosilauke in the White Mountains of New Hampshire, USA. Spectral reflectance (300-1100 nm wavelengths) and the chlorophyll fluorescence F(v)/F(m) ratio were measured on dark-adapted needles. Foliar morphology (needle size, shape, and mass) and nitrogen concentrations were measured in the laboratory. Reflectance spectra varied between species and with elevation. Two chlorophyll measures, red edge position and a chlorophyll-based difference index (Chl NDI = R750 - R705/R750 + R705), indicated more chlorophyll in fir than in spruce and decreasing chlorophyll with increasing elevation in both species. The structure-independent pigment index (SIPI = R800 - R445/R800 - R680) increased with elevation, indicating an increasing carotenoid : chlorophyll ratio. The photochemical reflectance index (PRI = R531 - R570/R531 + R570), a measure of photosynthetic radiation use efficiency, decreased with increasing elevation up to 1370 m. In the highest elevation site, within the stunted alpine krummholz at 1460 m, PRI was higher than at 1370 m, but still lower than at 1070 m. This same pattern was evident in the chlorophyll fluorescence F(v)/F(m) measurements. These independent indices indicate higher stress in spruce than fir, which may be related to the "spruce decline" reported in the northeastern USA. Results also indicate progressively increasing stress with increasing elevation up to 1370 m. Stress appears to be lower at 1460 m than at 1370 m, despite the harsher conditions at the very summit of Mt. Moosilauke. This may be a consequence of stress-tolerant physiology and/or prostrate architecture.

Acclimation of Myrtus communis to contrasting Mediterranean light environments — effects on structure and chemical composition of foliage and plant water relations

Leaf anatomical and chemical characteristics, water relations and stomatal regulation were studied in the shrub Myrtus communis growing under two contrasting Mediterranean light environments (full light versus 30% of full light) during the spring–summer period. These studies aimed to assess plant response to the combined effects of light and water availability. Foliar morphology, anatomy and chemistry composition acclimated positively to light conditions. Leaves of sun-exposed plants were thicker (38.7%) than those of shaded plants, mainly due to increased palisade parenchyma thickness, had a higher nitrogen concentration and stomatal density than the shade ones, which maximized foliar area (>SLA) and Chl/N molar ratio to improve light interception. Chlorophyll concentration per leaf area (Chl a) was always higher in sun leaves while, as expressed on dry mass (Chl m), significant differences were only apparent in September, shade leaves presenting higher values. During the summer period Chl a and Chl m markedly declined in sun leaves and remained unchanged in shade ones. The ratio of chlorophyll a/b was not affected either by the light intensity or by the season. Shade leaves presented generally a higher concentration of soluble carbohydrates per dry mass. No significant differences in starch concentration were apparent between sun and shade leaves and a gradual depletion occurred during the water stress period. Maximum stomatal conductances correlated positively with predawn water potential. Throughout the season, sun plants always presented higher leaf conductance to water vapour and lower minimum leaf water potentials, indicating an interaction of light–environment on these water relation parameters. Stomatal closure constitutes a mechanism to cope with diurnal and seasonal water deficits, sun plants presenting a more efficient control of water losses during water deficiency period. In addition, both sun and shade plants evidenced leaf osmotic adjustment ability in response to water stress, which was greater in sun ones.

Influence of nutrient supply on shade-sun acclimation of Picea abies seedlings: effects on foliar morphology, photosynthetic performance and growth.

Norway spruce seedlings (Picea abies Karst.) were grown in low light for one year, under conditions of adequate and limiting nutrition, then transferred to high light. Three months after transfer we measured photosynthesis, leaf nitrogen concentration, leaf chlorophyll concentration and leaf mass per area (LMA) of current-year and 1-year-old shoots; silhouette area ratio (SAR, the ratio of shoot silhouette area to projected needle area) was also measured in current-year shoots. At the foliage level, the effects of light and nutrient treatments differed markedly. Light availability during foliage expansion primarily affected LMA and SAR (morphological acclimation at the needle and shoot level, respectively). By contrast, nutrient supply in high light affected photosynthetic capacity per unit of leaf tissue (physiological acclimation at the cellular level) but did not affect LMA and SAR. The capacity for shade-sun acclimation in foliage formed before transfer to high light differed greatly from that of foliage formed following the transfer. The morphological inflexibility of mature needles (measured by LMA) limited their shade-sun acclimation potential. In contrast, at high nutrient supply, shoots that developed just after the change in photosynthetic photon flux density largely acclimated, both morphologically and physiologically, to the new light environment. The acclimation response of both current- and 1-year-old shoots was prevented by nutrient limitation. Analysis of growth at the whole-plant level largely confirmed the conclusions drawn at the shoot level. We conclude that nutrient shortage subsequent to the opening of a canopy gap may strongly limit the acclimation response of Norway spruce seedlings. Successful acclimation was largely related to the plant's ability to produce sun foliage and adjust whole-plant biomass allocation rapidly.

Molecular and morphological variation in the Senna artemisioides complex

The Senna artemisioides species complex is characterised by extremely variable foliar morphology. This paper presents the results of an integrative study on reproductive biology, morphology and genetic variation to explore the evolutionary and systematic relationships within this species complex at Idalia National Park in central Queensland. Senna artemisioides showed discontinuous variation at both genetic and phenotypic level. At three sites, foliar morphology was discontinuous, being represented as discrete clusters. Analysis of isozyme variation indicated that many of the discrete morphological groups are distinguished by fixed genetic differences. Morphotypes were also characterised by widespread monomorphism. Most of the genetic variation was between morphotypes rather than within morphotypes. These fixed genetic differences indicate a lack of gene flow between morphotypes and therefore an absence of hybridisation. The two most distinct morphological groups (pyllodinous, pinnate) had high genetic distances of 0.5, a value beyond the usual distance between congeneric species. Forty-two percent of pairwise comparisons between other morphotypes yielded genetic distance values that were relatively high (0.21–0.42). Some phenotypically distinct morphotypes, however, showed little or no isozyme divergence. The combined evidence suggests that genetically distinct morphotypes are independent lineages originating from an ancestral sexual reproductive event that is perpetuated by apomictic reproduction.

Research review. Components of leaf dry mass per area – thickness and density – alter leaf photosynthetic capacity in reverse directions in woody plants

The relationships of foliage assimilation capacity per unit area (PPmax) with leaf dry mass per unit area (LMA) and nitrogen content per unit area (NP) differ between species and within species grown in different habitats. To gain a more mechanistic insight into the dependencies of PPmax on LMA and NP, this literature study based on 597 species from a wide range of earth biomes with woody vegetation examines the relations between leaf photosynthetic capacity and the components of LMA (leaf density (D, dry mass per volume) and thickness (T)), and also the correlations of D and T with leaf nitrogen content and fractional leaf volumes in different tissues. Across all species, PPmax varied 12‐fold and photosynthetic capacity per unit dry mass (Pmmax) 16‐fold, NP 12‐fold, and nitrogen per unit dry mass (Nm) 13‐fold, LMA 46‐fold, D 13‐fold, and T 35‐fold, indicating that foliar morphology was more plastic than foliar chemistry and assimilation rates. Although there were strong positive correlations between PPmax and NP, and between Pmmax and Nm, leaf structure was a more important determinant of leaf assimilation capacities. PPmax increased with increasing LMA and T, but was independent of D. By contrast, Pmmax scaled negatively with LMA because of a negative correlation between Pmmax and D, and was poorly related to T. Analysis of leaf nitrogen and tissue composition data indicated that the negative relationship between D and Pmmax resulted from negative correlations between D and Nm, D and volumetric fraction of leaf internal air space, and D and symplasmic leaf fraction. Thus, increases in leaf density bring about (1) decreases in assimilative leaf compounds, and (2) extensive modifications in leaf anatomy that may result in increases in intercellular transfer resistance to CO2. Collectively, (1) and (2) lead to decreased Pmmax, and also modify PPmax versus LMA relationships.

Aboveground modular component responses to intraspecific competition within density-stressed black spruce stands

A broad range of measures of aboveground growth were used to assess whether competition occurs by processes of resource depletion or resource preemption within monospecific, even-aged, density-stressed, and spatially heterogeneous black spruce (Picea mariana (Mill.) BSP) stands. The assessments proceeded by evaluating the relationships between relative growth and partitioning indices of individual subject trees and directional-specific indices of cumulative competition. Significant directional-specific asymmetrical relationships between subject trees and their local competitors were found, indicating the occurrence of competition by resource preemption. All measures of growth, however, did not respond to directional-specific competition to the same degree. Larger responses, characterizing the response of black spruce trees to increasing competition from their larger neighbours, involved decreased branch production and changes in foliar morphology. Such adaptive, plastic responses in phenotype, combined with lesser responses of foliage production and nutrient concentrations, suggest a strategy used by black spruce to compete within density-stressed populations situated on nutrient-limiting sites: decreased allocation of resources to nonphotosynthetic components, maintenance of the photosynthetic apparatus through adjustments in foliage morphology, and nutrient conservation through foliage retention.

An analysis of light effects on foliar morphology, physiology, and light interception in temperate deciduous woody species of contrasting shade tolerance.

Maximum Rubisco activities (V(cmax)), rates of photosynthetic electron transport (J(max)), and leaf nitrogen and chlorophyll concentrations were studied along a light gradient in the canopies of four temperate deciduous species differing in shade tolerance according to the ranking: Populus tremula L. < Fraxinus excelsior L. < Tilia cordata Mill. = Corylus avellana L. Long-term light environment at the canopy sampling locations was characterized by the fractional penetration of irradiance in the photosynthetically active spectral region (I(sum)). We used a process-based model to distinguish among photosynthesis limitations resulting from variability in fractional nitrogen investments in Rubisco (P(R)), bioenergetics (P(B), N in rate-limiting proteins of photosynthetic electron transport) and light harvesting machinery (P(L), N in chlorophyll and thylakoid chlorophyll-protein complexes). On an area basis, V(cmax) and J(max) (V(a) (cmax) and J(a) (max)) increased with increasing growth irradiance in all species, and the span of variation within species ranged from two (T. cordata) to ten times (C. avellana). Examination of mass-based V(cmax) and J(max) (V(m) (cmax) and J(m) (max)) demonstrated that the positive relationships between area-based quantities and relative irradiance mostly resulted from the scaling of leaf dry mass per area (M(A)) with irradiance. Although V(m) (cmax) and J(m) (max) were positively related to growth irradiance in C. avellana, and J(m) (max) was positively related to irradiance in P. tremula, the variation range was only a factor of two. Moreover, V(m) (cmax) and J(m) (max) were negatively correlated with relative irradiance in T. cordata. Rubisco activity in crude leaf extracts generally paralleled the gas-exchange data, but it was independent of light in T. cordata, suggesting that declining V(m) (cmax) with increasing relative irradiance was related to increasing diffusive resistances from the intercellular air spaces to the sites of carboxylation in this species. Because irradiance had little effect on foliar nitrogen concentration, the relationships of P(B) and P(R) with irradiance were similar to those of V(m) (cmax) and J(m) (max). Shade-intolerant species tended to have greater P(B) and P(R) and also larger V(a) (cmax) and J(a) (max) than more shade-tolerant species. However, for the whole material, P(B) and P(R) varied only about 50%, whereas V(a) (cmax) and J(a) (max) varied more than 15-fold, further emphasizing the importance of leaf anatomical plasticity in determining photosynthetic acclimation to high irradiance. Leaf chlorophyll concentrations and fractional nitrogen investments in light harvesting increased hyperbolically with decreasing irradiance to improve quantum use efficiency for incident irradiance. The effect of irradiance on P(L) was of the same order as its effect in the opposite direction on M(A), leading to either a constant model estimate of leaf absorptance with I(sum) or a slightly positive correlation. We conclude that leaf morphological plasticity is a more relevant determinant of foliage adaptation to high irradiance than foliage biochemical properties, whereas biochemical adaptation to low irradiance is of the same magnitude as the anatomical adjustments. Although shade-tolerant species did not have greater chlorophyll concentrations and P(L) than shade-intolerant species, they possessed lower M(A), and could maintain a more extensive foliar display for light capture with constant biomass investment in leaves.

Stoichiometry of foliar carbon constituents varies along light gradients in temperate woody canopies: implications for foliage morphological plasticity.

Foliar morphology and chemical composition were examined along a light gradient in the canopies of five deciduous temperate woody species, ranked according to shade-tolerance as Populus tremula L. < Fraxinus excelsior L. < Tilia cordata Mill. = Corylus avellana L. < Fagus sylvatica L. Foliar carbon was divided between structural (cell-wall polysaccharides, lignin) and nonstructural (proteins, ethanol-soluble carbohydrates, starch) fractions. Foliar morphology of all species was strongly affected by irradiance. Both leaf dry mass per area (M(A)), a product of leaf density and thickness, and leaf dry to fresh mass ratio (D(w)), characterizing the apoplastic leaf fraction, increased with increasing relative irradiance (I(sum), calculated as the weighted mean of fractional penetration of diffuse and direct irradiance). Though the relationships were qualitatively identical among the taxa, more shade-tolerant species generally had lower values of M(A) than shade-intolerant species, and their morphological relationships with irradiance were curvilinear; however, there were no signs of saturation even at the highest irradiances in shade-intolerant species. In all species, lignin concentrations increased and cell-wall polysaccharide concentrations decreased with increasing irradiance. Consequently, biomass investment in structural leaf components appeared to be relatively constant along light gradients. The relationship between irradiance and structural compounds tended to be asymptotic in the more shade-tolerant species, whereas M(A) was linearly correlated with concentrations of structural leaf components, suggesting that similar factors were responsible for the curvature in the morphological and chemical relationships with irradiance. Because lignin increases tissue elastic modulus thereby rendering leaves more resistant to low leaf water potentials, we conclude that changes in stoichiometry of cell wall components were related to foliage acclimation to the gradients of water deficit that develop in the canopy and inherently accompany light gradients. We also conclude that increased lignification decreased leaf expansion growth, and that species differences in lignification were partly responsible for the observed interspecific variability in morphological plasticity. Analysis of structural leaf compounds provided no indication of how shade-intolerant species with low investments in lignin acclimated to gradients of water availability in the canopy. Because shade-intolerant species generally had higher capacities for photosynthesis than shade-tolerant species, we postulated that they should also have a greater ability for osmotic adjustment of leaf water potential with photosynthates. The concentrations of soluble carbohydrates increased with increasing irradiance in all species; however, the osmotic adjustment achieved in this way was similar in all species, except for shade-intolerant F. excelsior, which had a lower potential for osmotic adjustment with carbohydrates than the other taxa. Although we did not determine whether the gradients of stem water potential and leaf water deficits were similar in canopies of different species, we demonstrated that water relations play a central role in determining foliar structure and composition along light gradients in the canopy.

Are compound-leaved woody species inherently shade-intolerant? An analysis of species ecological requirements and foliar support costs

Comparisons among European, Japanese and North-American temperate deciduous woody floras revealed that there is no difference in shade-tolerance or in successional position between the compound- and simple-leaved species. Given that the compound-leaved species usually have greater biomass investments in non-productive throwaway supporting structures, it remained unclear how they could be as shade-tolerant as the simple-leaved analogues. To find out the role of the variability in leaf structure and composition in shade-tolerance of these species, foliar morphology and chemistry were analysed in 15 Estonian temperate compound-leaved deciduous woody taxa.