Scaling the leaf length-times-width equation to predict total leaf area of shoots

Background and AimsAn individual plant consists of different-sized shoots, each of which consists of different-sized leaves. To predict plant-level physiological responses from the responses of individual leaves, modelling this within-shoot leaf size variation is necessary. Within-plant leaf trait variation has been well investigated in canopy photosynthesis models but less so in plant allometry. Therefore, integration of these two different approaches is needed.MethodsWe focused on an established leaf-level relationship that the area of an individual leaf lamina is proportional to the product of its length and width. The geometric interpretation of this equation is that different-sized leaf laminas from a single species share the same basic form. Based on this shared basic form, we synthesized a new length-times-width equation predicting total shoot leaf area from the collective dimensions of leaves that comprise a shoot. Furthermore, we showed that several previously established empirical relationships, including the allometric relationships between total shoot leaf area, maximum individual leaf length within the shoot and total leaf number of the shoot, can be unified under the same geometric argument. We tested the model predictions using five species, all of which have simple leaves, selected from diverse taxa (Magnoliids, monocots and eudicots) and from different growth forms (trees, erect herbs and rosette herbs).Key ResultsFor all five species, the length-times-width equation explained within-species variation of total leaf area of a shoot with high accuracy (R² > 0.994). These strong relationships existed despite leaf dimensions scaling very differently between species. We also found good support for all derived predictions from the model (R² > 0.85).ConclusionsOur model can be incorporated to improve previous models of allometry that do not consider within-shoot size variation of individual leaves, providing a cross-scale linkage between individual leaf-size variation and shoot-size variation.     

Different-sized oak trees are equally protected by the aphid-tending ants

Theoretical models predict that the ecological impacts of ants on plants will vary with the size of the plant, but experimental evidence supporting this hypothesis is lacking. Focusing on aphid-tending ants, Lasius fuliginosus, and host oak trees, Quercus liaotungensis, we surveyed the density of aphids on the leaves of different-sized trees and the relationship between the densities of aphids and ants on the leaves. We then evaluated the impacts of ants on small (diameter at breast height (DBH) < 5 cm) and large trees (DBH > 25 cm). The field survey showed that the density of ants on leaves was determined by the density of aphids and the latter was similar among different-sized trees; through an ant-exclusion treatment, we found that the impacts of ants on plants, aphids, caterpillars, and galls did not differ by the size of the tree. L. fuliginosus had a significant protective effect for Q. liaotungensis, but this effect did not convert to enhanced fruit production during the 2-year study period. Considering that size can be used as an indicator of a plant’s ontogenetic stage, our results indicate that with similar densities of aphids and, in turn, ants on their canopy, trees at early and later ontogenetic stages are equally protected by aphid-tending ants.     

Plant defense, herbivory, and the growth of Cordia alliodora trees and their symbiotic Azteca ant colonies

The effects of herbivory on plant fitness are integrated over a plant??s lifetime, mediated by ontogenetic changes in plant defense, tolerance, and herbivore pressure. In symbiotic ant?Cplant mutualisms, plants provide nesting space and food for ants, and ants defend plants against herbivores. The benefit to the plant of sustaining the growth of symbiotic ant colonies depends on whether defense by the growing ant colony outpaces the plant??s growth in defendable area and associated herbivore pressure. These relationships were investigated in the symbiotic mutualism between Cordia alliodora trees and Azteca pittieri ants in a Mexican tropical dry forest. As ant colonies grew, worker production remained constant relative to ant-colony size. As trees grew, leaf production increased relative to tree size. Moreover, larger trees hosted lower densities of ants, suggesting that ant-colony growth did not keep pace with tree growth. On leaves with ants experimentally excluded, herbivory per unit leaf area increased exponentially with tree size, indicating that larger trees experienced higher herbivore pressure per leaf area than smaller trees. Even with ant defense, herbivory increased with tree size. Therefore, although larger trees had larger ant colonies, ant density was lower in larger trees, and the ant colonies did not provide sufficient defense to compensate for the higher herbivore pressure in larger trees. These results suggest that in this system the tree can decrease herbivory by promoting ant-colony growth, i.e., sustaining space and food investment in ants, as long as the tree continues to grow.     

Growing larger with domestication: a matter of physiology,morphology or allocation?

• Domestication might affect plant size. We investigated whether herbaceous crops are larger than their wild progenitors, and the traits that influence size variation.
• We grew six crop plants and their wild progenitors under common garden conditions. We measured the aboveground biomass gain by individual plants during the vegetative stage. We then tested whether photosynthesis rate, biomass allocation to leaves, leaf size and specific leaf area (SLA) accounted for variations in whole‐plant photosynthesis, and ultimately in aboveground biomass.
• Despite variations among crops, domestication generally increased the aboveground biomass (average effect +1.38, Cohen's d effect size). Domesticated plants invested less in leaves and more in stems than their wild progenitors. Photosynthesis rates remained similar after domestication. Variations in whole‐plant C gains could not be explained by changes in leaf photosynthesis. Leaves were larger after domestication, which provided the main contribution to increases in leaf area per plant and plant‐level C gain, and ultimately to larger aboveground biomass.
• In general, cultivated plants have become larger since domestication. In our six crops, this occurred despite lower investment in leaves, comparable leaf‐level photosynthesis and similar biomass costs of leaf area (i.e. SLA) than their wild progenitors. Increased leaf size was the main driver of increases in aboveground size. Thus, we suggest that large seeds, which are also typical of crops, might produce individuals with larger organs (i.e. leaves) via cascading effects throughout ontogeny. Larger leaves would then scale into larger whole plants, which might partly explain the increases in size that accompanied domestication.

     

Growth-unit structure in trees: effects of branch category and position on Nothofagus nervosa, N. obliqua and their hybrids (Nothofagaceae)

In plants with rhythmic growth, a branch segment extended in one event is known as growth unit (GU). GU structure, resulting from the resources allocated to stem length, volume and mass, and to leaf area and mass, is relevant for understanding branch functioning in the context of plant development. This study compares GU structure between main branches and short branches positioned at low and high positions on nursery-grown trees of three closely related genetic entities: Nothofagus nervosa, N. obliqua and natural hybrids between these species. GUs of short branches, compared to those of main branches, had lower length, diameter and number of leaves, and higher specific leaf area (SLA), stem density and proportional mass in leaves than in stems. GUs at high position on the trees had a higher proportion of their mass in stem than in leaves and a lower SLA than those at low position. Stem density was higher for N. nervosa and the hybrid trees than for N. obliqua. Most other GU traits did not differ statistically between the considered genetic entities. The three genetic entities exhibited distinct patterns of variation in leaf size with leaf position along main-branch GUs. The individual tree had a significant effect on most variables. GU structure would have a major ontogenetic component and would play a relevant role in the architecture of Nothofagus species and their adaptation to different environmental conditions.     

Photosynthetic capacity,irradiance and sequential senescence of sugar beet leaves

In field-grown sugar beet plants (Beta vulgaris L. cv. Dobrovická A), each of66 successive leaves produoed in the course of the vegetation period was different with respect to its photosynthetic capaoity (P_c), life span, duration of leaf area expansion, and longevity after its maximum leaf area (A_max) has developed. The proportionality between the seasonal changes in these characteristics was not the same if the sequential senescence of leaves was taken into account. With aging of individual leaves, P_c increased with the leaf area expansion having attained the peak value between 75% to 100% of A_max The rate of ontogenetic changes in P_c of each leaf was specified by the rate of its growth and development so that even at comparable ages the successive leaves constituted a series of different physiological units. The seasonal changes in quantum irradiance (PAR) were found to be responsible for differences in the growth characteristics between the successive leaves: Leaf expansion period was related with daily integrals of the incoming PAR (Io), while leaf longevity, after the A_max had been attained, was closely linked with PAR intercepted by the canopy (I). P_c expressed per the total leaf area of the plant was significantly correlated withI, while P_c calculated per unit leaf area of the plant was related toI _o Leaf potential to adapt P_c correspondingly to changes in PAR was greatest during leaf blade expansion; after the leaf had ceased to expand, changes in P_c were independent of differences in leaf irradiance. The results stress, at least for field conditions, the inadmissibility of the extrapolation of attributes from one leaf to the other ones sequentially senescing on the plant.     

Herbivory alters plant carbon assimilation,patterns of biomass allocation and nitrogen use efficiency

Herbivory can trigger physiological processes resulting in leaf and whole plant functional changes. The effects of chronic infestation by an insect on leaf traits related to carbon and nitrogen economy in three Prunus avium cultivars were assessed. Leaves from non-infested trees (control) and damaged leaves from infested trees were selected. The insect larvae produce skeletonization of the leaves leaving relatively intact the vein network of the eaten leaves and the abaxial epidermal tissue. At the leaf level, nitrogen content per mass (N_mass) and per area (N_area), net photosynthesis per mass (A_mass) and per area (A_area), photosynthetic nitrogen-use efficiency (PNUE), leaf mass per area (LMA) and total leaf phenols content were measured in the three cultivars. All cultivars responded to herbivory in a similar fashion. The N_mass, A_mass, and PNUE decreased, while LMA and total content of phenols increased in partially damaged leaves. Increases in herbivore pressure resulted in lower leaf size and total leaf area per plant across cultivars. Despite this, stem cumulative growth tended to increase in infected plants suggesting a change in the patterns of biomass allocation and in resources sequestration elicited by herbivory. A larger N investment in defenses instead of photosynthetic structures may explain the lower PNUE and A_mass observed in damaged leaves. Some physiological changes due to herbivory partially compensate for the cost of leaf removal buffering the carbon economy at the whole plant level.     

Structural and functional variability within the canopyand its relevance for carbon gain and stress avoidance

The functional variability in leaf angle distribution within the canopy was analysed with respect to regulation of light interception and photoprotection. Leaf orientation strongly determined the maximum photochemical efficiency of PSII (F_v/F_m) during summer: horizontal leaves were highly photoinhibited whereas vertical leaf orientation protected the leaves from severe photoinhibition. The importance of leaf orientation within the canopy was analysed in two Mediterranean macchia species with distinct strategies for drought and photoinhibition avoidance during summer. The semi-deciduous species (Cistus monspeliensis) exhibited strong seasonal but minimal spatial variability in leaf orientation. Reversible structural regulation of light interception by vertical leaf orientation during summer protected the leaves from severe photoinhibition. The evergreen sclerophyll (Quercus coccifera) exhibited high spatial variability in leaf angle distribution throughout the year and was less susceptible to photoinhibition. The importance of both strategies for plant primary production was analysed with a three-dimensional canopy photoinhibition model (CANO-PI). Simulations indicated that high variability in leaf angle orientation in Q. coccifera resulted in whole-plant carbon gain during the summer, which was 94 % of the maximum rate achieved by theoretical homogeneous leaf orientations. The high spatial variability in leaf angle orientation may be an effective compromise between efficient light harvesting and avoidance of excessive radiation in evergreen plants and may optimize annual primary production. Whole plant photosynthesis was strongly reduced by water stress and photoinhibition in C. monspeliensis; however, the simulations indicated that growth-related structural regulation of light interception served as an important protection against photoinhibitory reduction in whole-plant carbon gain.     

Short-term responses of leaf growth rate to water deficit scale up to whole-plant and crop levels: an integrated modelling approach in maize

Physiological and genetic studies of leaf growth often focus on short-term responses, leaving a gap to whole-plant models that predict biomass accumulation, transpiration and yield at crop scale. To bridge this gap, we developed a model that combines an existing model of leaf 6 expansion in response to short-term environmental variations with a model coordinating the development of all leaves of a plant. The latter was based on: (1) rates of leaf initiation, appearance and end of elongation measured in field experiments; and (2) the hypothesis of an independence of the growth between leaves. The resulting whole-plant leaf model was integrated into the generic crop model APSIM which provided dynamic feedback of environmental conditions to the leaf model and allowed simulation of crop growth at canopy level. The model was tested in 12 field situations with contrasting temperature, evaporative demand and soil water status. In observed and simulated data, high evaporative demand reduced leaf area at the whole-plant level, and short water deficits affected only leaves developing during the stress, either visible or still hidden in the whorl. The model adequately simulated whole-plant profiles of leaf area with a single set of parameters that applied to the same hybrid in all experiments. It was also suitable to predict biomass accumulation and yield of a similar hybrid grown in different conditions. This model extends to field conditions existing knowledge of the environmental controls of leaf elongation, and can be used to simulate how their genetic controls flow through to yield.     

A comparative analysis of leaf shape of wheat, barley and maize using an empirical shape model

Background and Aims

The phenotypes of grasses show differences depending on growth conditions and ontogenetic stage. Understanding these responses and finding suitable mathematical formalizations are an essential part of the development of plant and crop models. Usually, a marked change in architecture between juvenile and adult plants is observed, where dimension and shape of leaves are likely to change. In this paper, the plasticity of leaf shape is analysed according to growth conditions and ontogeny.

Methods

Leaf shape of Triticum aestivum, Hordeum vulgare and Zea mays cultivars grown under varying conditions was measured using digital image processing. An empirical leaf shape model was fitted to measured shape data of single leaves. Obtained values of model parameters were used to analyse the patterns in leaf shape.

Key Results

The model was able to delineate leaf shape of all studied species. The model error was small. Differences in leaf shape between juvenile and adult leaves in T. aestivum and H. vulgare were observed. Varying growth conditions impacted leaf dimensions but did not impact leaf shape of the respective species.

Conclusions

Leaf shape of the studied T. aestivum and H. vulgare cultivars was remarkably stable for a comparable ontogenetic stage (leaf rank), but differed between stages. Along with other aspects of grass architecture, leaf shape changed during the transition from juvenile to adult growth phase. Model-based analysis of leaf shape is a method to investigate these differences. Presented results can be integrated into architectural models of plant development to delineate leaf shape for different species, cultivars and environmental conditions.     

Development of the Fifth Leaf is Indicative for Whole Plant Performance at Low Temperature in Tomato

In the search for early-detectable selection criteria for growthat low temperature conditions in tomato, first the initiationand growth of individual leaves was analysed. Scanning electronmicroscopy revealed that the first four primordia had alreadydeveloped during the germination period at 25°C. The primordiumof the fifth leaf, however, was initiated after the transferof seedlings to the experimental conditions. The increase inlength of the first three leaves, and to a lesser extent ofthe fourth leaf, was considerably smaller in comparison withthat of later formed leaves. Moreover, the morphology of thefirst three to four leaves was deviant, whereas the others showedthe normal compound leaf architecture. All these results indicatedthat the fifth leaf was the earliest formed leaf with growthcharacteristics that might reflect the growth potential of thewhole plant. Development of the fifth leaf was tested as a marker for wholeplant growth. At three temperature, 18, 15 and 12°C, growthresponses of the fifth leaf were similar to that of whole plantsin four tomato genotypes: Line A, Line B, Premier and MXXIV-13.Significant differences in relative growth rate of dry weightof whole plants and fifth leaves (RGR_W)and of leaf area of thefifth leaves (RGR_LA between two fast growing and two slow growinggenotypes were found. No genotype by temperature interactionfor RGR_W and RGR_LA was found, indicating that the effect oftemperature decrease was similar for the four genotypes. The structure of the mature fifth leaf of one fast and one slowgrowing genotype, Line A and MXXIV-13, was analysed. For bothgenotypes, leaves were small and thick at low temperature, 12°C.The total number of epidermis and palisade parenchyma cellsper leaf was smaller but the size of the cells developed at12°C was larger than at 18°C. Consequently, the slowgrowth at 12°C was due to a low rate of cell division. Atboth temperatures, the fifth leaf to MXXIV-13 was smaller comparedto that of line A. Since the size of the cells were similar,the smaller leaf size was due to lower number of leaf cells. The results confirm the suitability of the growth, especiallyexpressed as RGR_LA , of the fifth leaf as a nondestructive marketfor vegetative development of tomato at low temperature. Growthdifferences between genotypes were mainly reflected by differencesin cell number of leaves, which might be correlated with geneticallydetermined differences in cell number of leaf primordia.Copyright1993, 1999 Academic Press Lycopersicon esculentum Mill. genotypes, plant growth, selection criteria, low temperature, leaf initiation, leaf development, RGR, leaf structure, cell expansion     

Sun-shade adaptability of the red mangrove,Rhizophora mangle (Rhizophoraceae): Changes through ontogeny at several levels of biological organization

Rhizophora mangle L., the predominant neotropical mangrove species, occupies a gradient from low intertidal swamp margins with high insolation, to shaded sites at highest high water. Across a light gradient, R. mangle shows properties of both “light-demanding” and “shade-tolerant” species, and defies designation according to existing successional paradigms for rain forest trees. The mode and magnitude of its adaptability to light also change through ontogeny as it grows into the canopy. We characterized and compared phenotypic flexibility of R. mangle seedlings, saplings, and tree modules across changing light environments, from the level of leaf anatomy and photosynthesis, through stem and whole-plant architecture. We also examined growth and mortality differences among sun and shade populations of seedlings over 3 yr. Sun and shade seedling populations diverged in terms of four of six leaf anatomy traits (relative thickness of tissue layers and stomatal density), as well as leaf size and shape, specific leaf area (SLA), leaf internode distances, disparity in blade–petiole angles, canopy spread: height ratios, standing leaf numbers, summer (July) photosynthetic light curve shapes, and growth rates. Saplings showed significant sun/shade differences in fewer characters: leaf thickness, SLA, leaf overlap, disparity in bladepetiole angles, standing leaf numbers, stem volume and branching angle (first-order branches only), and summer photosynthesis. In trees, leaf anatomy was insensitive to light environment, but leaf length, width, and SLA, disparities in bladepetiole angles, and summer maximal photosynthetic rates varied among sun and shade leaf populations. Seedling and sapling photosynthetic rates were significantly depressed in winter (December), while photosynthetic rates in tree leaves did not differ in winter and summer. Seasonal and ontogenetic changes in response to light environment are apparent at several levels of biological organization in R. mangle, within constraints of its architectural baiiplan. Such variation has implications for models of stand carbon gain, and suggest that response flexibility may change with plant age.     

The rates of shoot and root growth in intact plants of pea mutants in leaf morphology

Isogenic lines of pea (Pisum sativum L.) with the genetically determined changes in leaf morphology, afila (af) and tendril-less (tl), were used to study the relationship between shoot and root growth rates. The time-course of shoot and root growth was followed during the pre-floral period in the intact plants grown under similar conditions. The af mutation produced afila leaves without leaflets, whereas in the case of the tl mutations, tendrils were substituted with leaflets, and acacia-like leaves were developed. Due to the changes in leaf morphology caused by these mutations, pea genotypes differed in leaf area: starting from day 7, the leaf area was lower in the af plants and larger in the tl plants as compared to the wild-type plants. Such divergence was amplified in the course of plant development and reached its maximum immediately before the transition to flowering. Plants of isogenic lines did not notably differ in stem surface areas. In spite of significant difference in total leaf area, the wild type and tl plants did not differ in leaf dry weight. Starting from leaf 9, the af plants lagged behind two leaflet-bearing genotypes (wild type and tl) in leaf dry weight, whereas stem dry weight was similar in the wild type and tl forms and slightly lower in the af plants. Root dry weights were practically similar in the wild type and tl plants until flowering. The reduction of leaf area in the af plants drastically reduced root dry weight. In other words, the latter index was related to the total weight and total area of leaves and stems. The correlation analysis demonstrated an extremely low relationship between leaf and stem area and dry weight and those of roots early in plant development (when plants develop five to seven leaves). Later, immediately before flowering (nine to eleven leaves), root weight was positively related to leaf weight and area; however, stem area and root weight did not correlate. Thus, in three genotypes (wild type, af, and tl), at the end of their vegetative growth phase, leaf and root biomass accumulated in proportion, independently of leaf area expansion.     

Ontogenetic variations in leaf morphology of the tropical rain forest species Dipterocarpus alatus Roxb. ex G. Don

Under natural conditions ontogenetic development often coincides with changes in environmental factors. When explaining variations in leaf parameters, analyses based solely on environmental factors will lead to significant errors if the plant shows substantial ontogenetic variations in leaf properties. We evaluated intraspecific variations in eight morphological leaf traits of Dipterocarpus alatus over six architectural development stages under two different light conditions. An architectural analysis was conducted to distinguish precisely and objectively developmental stages of D. alatus. Leaves were collected on the most recent complete growth unit on the trunks of trees growing under two different light conditions. Eight leaf morphological traits were measured and calculated using ImageJ on greyscale images of leaf tracings. One-way ANOVA and Tukey tests were used to determine differences in leaf traits during ontogeny. The correlation coefficients were compared to determine whether leaf traits correlated more strongly with ontogenetic stage than with light intensity. D. alatus develops through a progressive transformation of its structure and architecture that adds one new axis category stage after stage. Specific leaf area, blade shape index and leaf dissection index decreased whereas blade area, perimeter, length, width and blade dry weight increased. Leaf traits correlated more strongly with ontogenetic stage than with light intensity. Our results demonstrated that studies on the responses of leaf traits to the environment may need to be corrected for an ontogeny effect. To strengthen this conclusion, future work should evaluate leaf variations during the ontogeny of different axis orders and/or axis categories.     

PLANT SIZE AND FORM IN THE UNDERSTORY PALM GENUS GEONOMA: ARE SPECIES VARIATIONS ON A THEME?

This study addressed the hypothesis that phylogenetic changes in plant size at reproductive maturity may have facilitated adaptive radiation of Geonoma species within rain forest understory habitats. Leaf size, leaf form, plant size, and growth form were compared within and among 23 species of Geonoma from lowland and montane rain forest areas of Costa Rica and Colombia. Leaf size was significantly correlated with crown height in 18 of the 21 species examined, and with stem diameter in 17 of the species. In species characterized by a gradual ontogenetic transition from bifid to dissected leaves, shoots with bifid leaves were significantly smaller than shoots with dissected leaves with respect to rachis length, number of plications, and stem diameter. Among species, stem diameter below the crown explained 74% of the variation in leaf size (rachis length). Crown height and stem diameter were positively correlated among clustered species, but not among solitary species or all species combined. Leaf dissection was correlated with crown height among the 17 species with dissected leaves; species with bifid leaves were significantly smaller than species with dissected leaves with respect to leaf size and stem diameter. Solitary species had larger leaves and larger stem diameters than clustered species at the same crown heights. Morphological patterns among species generally followed within-species trends. These patterns suggest that Geonoma species are variants on a generic theme:within and among species, leaf size and complexity of form increase with stem diameter and crown height. Solitary and clustered growth forms appear to be morphologically convergent; within each of these architectural groups, the generic theme still applies. Evolutionary changes in leaf size, leaf form, and plant size, however, have clearly involved other factors in addition to variation in plant size.     

Allometric co-variation of xylem and stomata across diverse woody seedlings

Leaf stomatal density is known to co-vary with leaf vein density. However, the functional underpinning of this relation, and how it scales to whole-plant water transport anatomy, is still unresolved. We hypothesized that the balance of water exchange between the vapour phase (in stomata) and liquid phase (in vessels) depends on the consistent scaling between the summed stomatal areas and xylem cross-sectional areas, both at the whole-plant and single-leaf level. This predicted size co-variation should be driven by the co-variation of numbers of stomata and terminal vessels. We examined the relationships of stomatal traits and xylem anatomical traits from the entire plant to individual leaves across seedlings of 53 European woody angiosperm species. There was strong and convergent scaling between total stomatal area and stem xylem area per plant and between leaf total stomatal area and midvein xylem area per leaf across all the species, irrespective of variation in leaf habit, growth-form or relative growth rate. Moreover, strong scaling was found between stomatal number and terminal vessel number, whereas not in their respective average areas. Our findings have broad implications for integrating xylem architecture and stomatal distribution and deepen our understanding of the design rules of plants' water transport network.     

Processes Driving Ontogenetic Succession of Galls in a Canopy Tree1

Herbivores can be associated with distinct ontogenetic stages of their host in a nonseasonal, directional, and continuous pattern of colonization and extinction of species populations called ontogenetic succession, but the processes behind this pattern are still largely unknown. We used plants of Cryptocarya aschersoniana Mez (Lauraceae) belonging to different ontogenetic stages, to examine how the density of different gall‐inducing insects varies along the ontogeny of the host, and how gall density is influenced by mechanisms associated with host quality (plant height, plant shape, leaf area, specific leaf area, and hypersensitivity), and by mechanisms associated with their natural enemies (parasitoids, pathogens, and predators). In a remnant of Araucaria Forest, located in the São Francisco de Paula National Forest (Brazil), gall density (ind./100 g of leaf ) was obtained for 42 plants of C. aschersoniana divided into three height classes. Two galling species were recorded, showing quite distinct density patterns among height classes of C. aschersoniana. While Hymenoptera gall density decreased almost 50 times from small plants to canopy trees, Hemiptera gall density increased almost 10 times. Path analyses showed that Hymenoptera density was higher in smaller plants, independent of other host traits, while Hemiptera density was higher in plants exhibiting smaller leaves. Natural enemies were not detected in the Hemiptera population, and mortality rates due to predators, parasitoids, and pathogens did not affect Hymenoptera density. Processes associated with plant quality play the main role in generating the observed ontogenetic succession pattern.     

Modular growth and functional heterophylly of the phreatophyte Ziziphus lotus: A trait-based study

The variation of plant functional traits, from the cell to the whole-plant level, is a central question in trait-based ecology with regard to understanding ecological strategies and adaptations that result from environmental drivers. Here, we analyzed whole-plant and leaf traits of the phreatophyte Ziziphus lotus (L.) Lam., a long-lived shrub that dominates one of the few terrestrial groundwater-dependent ecosystems (GDEs) in Mediterranean Basin drylands. We (a) assessed architectural traits and growth patterns, (b) analyzed leaf morpho-functional traits (specific leaf area [SLA] and stomata pore index [SPI]) and physiological traits (gas exchange rates), as well as their variations within individuals, and (c) evaluated temporal variations in modular growth (i.e., sequential iteration of structural units) between growing seasons and in leaf traits within seasons. Z. lotus' growth pattern was based on the repetition of modules composed of shoots (short and long) and branches (flowering and plagiotropic) that promoted a functional differentiation between vegetative and reproductive structures, respectively. We identified morpho-functionally distinct leaves (i.e., heterophylly) borne on different types of branches. Leaves on flowering branches had higher SLA and water use efficiency (WUEi), but lower SPI and transpiration rates than leaves on vegetative ones. We also observed trade-offs in the elongation of vegetative and flowering structures between growing seasons: the shorter the long shoots, the larger the flowering branches. The modular differentiation and heterophylly of Z. lotus might contribute to prioritizing the investment of resources of this phreatophyte, either for growth or reproduction, and could improve the efficiency in uptake and conservation of resources in drylands.     

Leaf Ecology of Pre-reproductive Ontogenetic Stages of the Palm TreeEuterpe edulisMart. (Arecaceae)

We studied leaves of 208 seedlings (S), infants (I) and juveniles(J) ofEuterpe edulis,randomly selected from plants in 1 ha ofswampy forest in SE Brazil. Each new leaf began extending afterthe complete development of the preceding leaf. The sequencesteps of leaf growth were emergence, linear growth while closed,opening of segments and logarithmic growth of the petiole. Averageleaf production rate (2.21 leaves per plant year^-1) did notvary among ontogenetic stages, conforming to a plastochronicrhythm. Average linear growth rate of the closed leaf was directlyrelated to average area of the open lamina. Herbivores attacked33.0% of all leaves giving rise to up to 10% loss of area andincluded damping-off-inducing suckers (7.1%), ordinary suckers(9.8%), chewers (5.4%), miners (2.7%) and multiple attacks (8.0%).These attacks varied among stages (S=22.4%, I=38.1%, J=33.3%),as did leaf mortality rates (S=26.5%, I=14.3% and J=0.0%). Unknownfactors were the main cause of leaf mortality (S=14.3%, I=7.1%).Not losing a leaf while a seedling and attaining a minimum leafarea in the infant stage were critical events for survival.Plants gained leaf area by not losing leaves while a seedling,by producing larger leaves with greater growth rates, and byaccumulating leaves with longer lifespans. The petiole can simulatean energetically cheaper branch, delimit a vital space aroundthe stem, favourably position the leaf lamina and substituteprovisionally for stem growth in height.Copyright 1999 Annalsof Botany Company Arecaceae,Euterpe edulis, herbivory, leaf ecology, leaf growth, leaf production, semideciduous forest, southeastern Brazil.     

Variation of leaf traits and pigment content in three species of steppe plants depending on the climate aridity

Mesophyll structure and content of photosynthetic pigments in the leaves of three species of steppe plants, Centaurea scabiosa L., Euphorbia virgata Waldst. et Kit., Helichrysum arenarium (L.) Moench, were investigated in four geographical sites of the Volga region and the Urals located in the forest-steppe and steppe zones. Variations of the studied parameters between geographical points depended both on the species and on the structural organization of the leaf. The highest level of variation was observed for leaf area and pigment content per unit leaf area, the size and the number of chloroplasts in the cell changed to a lesser extent. The leaf thickness, leaf area and mesophyll cell sizes mostly depended on the plant species. C. scabiosa had large leaves (40–50 cm²) with large thickness (280–290 μm) and large mesophyll cells (up to 15000 μm³). The leaves of H. arenarium and E. virgata were ten times smaller and characterized by 1.5 times smaller thickness and 2?3 times smaller cell size. Geographical location and climate of the region affected leaf density, proportion of partial tissue volume, and the ratio of the photosynthetic pigments. In the southern point of Volga region with the highest climate aridity, all studied species were characterized by maximum values of volumetric leaf density (LD), due to the high proportion of sclerenchyma and vascular bundles, and specificity of the mesophyll structure. With the decline in latitude, chlorophyll (Chl) and carotenoid (Car) contents in leaf area were reduced, the ratio Chl/Car was increased, and the ratio Chl a/b was declined. The reduction of the pigment content in the leaf in all species was associated with a reduction in the amount of Chl per chloroplast, and for C. scabiosa and H. arenarium it was associated also with the reduction of chloroplast amount in the leaf area. In turn, chloroplast number per leaf area and the total cell area (A_mes/A) depended on the ratio of the number and size of mesophyll cells inherent to this plant species. At the same time, we found a similar mechanism of spatial organization of leaf restructuring for all studied species—decrease in A_mes/A was accompanied by increasing in the proportion of intercellular air spaces in the leaf. It is concluded that variations in structural and functional parameters of the photosynthetic apparatus of steppe plants were associated with plant adaptation to climate features. General direction of the changes of leaf parameters of the studied species with aridity was the increase of LD and the decrease of pigment content per leaf area however the cellular mechanisms of changes in the pigment content and integral parameters of mesophyll were determined by the plant species properties.