Article
To read the full-text of this research, you can request a copy directly from the authors.

Abstract

Geoxyles and their congeneric tree species are a very common feature in the Zambezian Floristic Region, however , little is known about differing expression of plant functional traits between the two life forms and thus their evolutionary adaptations to prevailing habitat conditions. Therefore, we measured selected plant functional traits and compared them between the geoxyle and tree growth forms. We selected six species pairs that are common in the study area, i.e. Brachystegia russelliae vs. Brachystegia longifolia (FabaceaeÀDetarioideae); Cryptosepalum exfoliatum subsp. suffruticans vs. Cryptosepalum exfoliatum subsp. pseudotaxus (Faba-ceaeÀDetarioideae); Combretum platypetalum vs. Combretum zeyheri (Combretaceae); Parinari capensis vs. Pari-nari curatellifolia (Chrysobalanaceae); Syzygium guineense subsp. macrocarpum (suffrutex form vs. tree form) (Myrtaceae); Uapaca nitida var. suffrutescens vs. Uapaca nitida var. nitida (Phyllanthaceae). For analysis we selected traits reflecting adaptations to environmental conditions such as specific leaf area (SLA), leaf thickness (LT), wood density (WD), leaf nitrogen (LN), leaf carbon (LC), leaf phosphorus (LP), leaf calcium (LCa), leaf magnesium (LMg), leaf potassium concentrations (LP) and leaf dry matter content (LDMC). Additionally, we measured leaf water potential (WP) during dry and wet seasons. The results did not show a general pattern of inter-life-form trait variation among trees and geoxyles. There were significant differences in LA, WD, LN, LC, LMg and LK between geoxyles and trees, but mostly among species pairs. This indicates that the growth form transition is largely decoupled from leaf economics. Thus, the detected differences in plant functional traits among the species pairs are mostly taxon related responses to specific environmental stresses and habitat conditions.

No full-text available

Request Full-text Paper PDF

To read the full-text of this research,
you can request a copy directly from the authors.

ResearchGate has not been able to resolve any citations for this publication.
Article
Full-text available
This review summarizes current understanding of five key plant traits: seed mass, plant height, wood density, leaf mass per unit area and leaf size, emphasizing ways in which our understanding of large-scale patterns in plant traits have improved over the last two decades. Notable advances include: (1) large-seeded species have greater seed dispersal distances than do small-seeded species, (2) leaf mass per unit area is not strongly or consistently related to plant traits outside the leaf economics spectrum, or to broad gradients in environmental conditions, and (3) fleshy fruit could not have first evolved for seed dispersal, as the first fleshy fruit appeared millions of years before the first potential seed dispersers. While quantifying large-scale patterns in plant traits has yielded many important discoveries, it is clear that the next major leap in understanding will not come from simply including ever more variables in our analyses. I suggest that we build upon Harper's “Darwinian approach to plant ecology” and apply evolutionary ideas to large-scale trait ecology. For example, quantifying trait impacts on lifetime fitness rather than on particular stages of plant regeneration can allow us to understand the coordination between seemingly disparate traits. I use this approach to bring seed mass and plant height together as integrated parts of a species’ life-history spectrum. I then point out problems associated with the implicit assumption that selection acts on species’ mean trait values and show how considering the way selection acts can improve our understanding of the effects of climate on plant traits. A goal for the future is to quantify the full suite of biotic and abiotic factors that shape plant strategy in complex, real-world situations. Synthesis. Enormous data availability and ever more powerful computational and statistical tools have given ecologists unprecedented power to quantify large-scale patterns in plant ecology. However, there is a limit to how far big data alone can take us. The time is ripe for a new generation of hypotheses and ecological theory built on strong evolutionary foundations. Let the creativity begin!. © 2017 The Author. Journal of Ecology
Article
Full-text available
It has been proposed in separate studies that fire or frost were the critical selective agents in the evolution of subshrub geoxyles (SGs) in African subtropical grasslands. We attempt to resolve this controversy by examining the evolution of SGs among the entire genus Protea that is widespread throughout southern/central Africa. We show that SGs are not confined to grasslands but occur in a wide range of non-forest types, including mediterranean shrublands. SG proteas arose 1−11 million years ago but their multiple origins among other geoxyles, confounded by strong intraspecific variability among grassland species, makes it impossible to identify the ancestral growth form. We conclude that the evolutionary history of SG proteas has occurred under lightning-prone conditions that promoted fire and were essentially frost-free; exposure to frost has been limited to certain elevated locations in more recent times. This is supported by many SGs having pyrogenic flowering and lack of seed storage among grassland species.
Article
Full-text available
An important aim of plant ecology is to identify leading dimensions of ecological variation among species and to understand the basis for them. Dimensions that can readily be measured would be especially useful, because they might offer a path towards improved worldwide synthesis across the thousands of field experiments and ecophysiological studies that use just a few species each. Four dimensions are reviewed here. The leaf mass per area-leaf lifespan (LMA-LL) dimension expresses slow turnover of plant parts (at high LMA and long LL), long nutrient residence times, and slow response to favorable growth conditions. The seed mass-seed output (SM-SO) dimension is an important predictor of dispersal to establishment opportunities (seed output) and of establishment success in the face of hazards (seed mass). The LMA-LL and SM-SO dimensions are each underpinned by a single, comprehensible tradeoff, and their consequences are fairly well understood. The leaf size-twig size (LS-TS) spectrum has obvious consequences for the texture of canopies, but the costs and benefits of large versus small leaf and twig size are poorly understood. The height dimension has universally been seen as ecologically important and included in ecological strategy schemes. Nevertheless, height includes several tradeoffs and adaptive elements, which ideally should be treated separately. Each of these four dimensions varies at the scales of climate zones and of site types within landscapes. This variation can be interpreted as adaptation to the physical environment. Each dimension also varies widely among coexisting species. Most likely this within-site variation arises because the ecological opportunities for each species depend strongly on which other species are present, in other words, because the set of species at a site is a stable mixture of strategies.
Article
Full-text available
The photosynthetic capacity of leaves is related to the nitrogen content primarily bacause the proteins of the Calvin cycle and thylakoids represent the majority of leaf nitrogen. To a first approximation, thylakoid nitrogen is proportional to the chlorophyll content (50 mol thylakoid N mol-1 Chl). Within species there are strong linear relationships between nitrogen and both RuBP carboxylase and chlorophyll. With increasing nitrogen per unit leaf area, the proportion of total leaf nitrogen in the thylakoids remains the same while the proportion in soluble protein increases. In many species, growth under lower irradiance greatly increases the partitioning of nitrogen into chlorophyll and the thylakoids, while the electron transport capacity per unit of chlorophyll declines. If growth irradiance influences the relationship between photosynthetic capacity and nitrogen content, predicting nitrogen distribution between leaves in a canopy becomes more complicated. When both photosynthetic capacity and leaf nitrogen content are expressed on the basis of leaf area, considerable variation in the photosynthetic capacity for a given leaf nitrogen content is found between species. The variation reflects different strategies of nitrogen partitioning, the electron transport capacity per unit of chlorophyll and the specific activity of RuBP carboxylase. Survival in certain environments clearly does not require maximising photosynthetic capacity for a given leaf nitrogen content. Species that flourish in the shade partition relatively more nitrogen into the thylakoids, although this is associated with lower photosynthetic capacity per unit of nitrogen.
Article
Full-text available
We tested the existence of general patterns in the photosynthetic metabolism of oxygen-evolving organisms, based on a compilation of data for 315 species ranging from cyanobacteria to tree leaves. We used thickness and chlorophyll a concentration of the photosynthetic structure (cell, thallus, leaf) to scale differences in photosynthetic metabolism among plants, because of the demonstrated importance of these plant traits in regulating light absorption properties and photosynthetic rates of particular plant groups. We examined only the properties of the photosynthetic structure because this is the plant unit responsible for the photosynthetic process and thus is closely related to plant productivity, whereas there is a lack of general quantitative descriptors of the whole organism useful for such broad-scale comparisons, and few studies report net photosynthetic rates of whole organisms, including respiration rates of all non-photosynthetic structures. The results demonstrated that descriptors of plant metabolism such as maximum net photosynthesis, initial slope of the photosynthesis-irradiance (PI) curve and dark respiration display strong positive interrelationships. The metabolic rates declined with increasing thickness of the photosynthetic structures and more steeply for photosynthesis than respiration. Photosynthetic rates also changed with increment of volume of the photosynthetic structure resembling patterns that have been previously described for animal metabolism related to body weight. The strong relationship of metabolic rate and chlorophyll a concentration to the thickness of photosynthetic tissue reflects broad-scale patterns and not the adaptive response of individual or closely-related species of similar tissue thickness to varying environmental conditions. Thickness of the photosynthetic structures, therefore, plays an important role in the environmental control of plant performance and, consequently, it might have been an important driver of plant evolution, setting thresholds to the metabolism and productivity of phototrophic organisms.
Article
Full-text available
Analysis of energy partitioning between defensive investments and growth in woody plants indicates that increasing a tree's life-span should require increased energy investment in protective measures such as thick bark and defensive chemicals. Increased investment in such defenses, however, logically must slow down the growth rate, thereby raising the mortality rate for juveniles in competition for height growth. Early reproduction should also reduce the growth rate. It is hypothesized that rapid growth can substitute for these defenses, but the consequence is rapid decline upon reaching maturity. These predictions are tested with data compiled from the literature for 159 species of North American trees. Data analysis supports predictions. Longevity of angiosperms, but not of gymnosperms was correlated with increased investment in defenses as measured by volumetric heat content of the wood. Wood density was not as good a measure. Longevity of gymnosperms was predicted by resistance to wood decay. For both taxa there was a negative correlation between growth rate and longevity, supporting the hypothesis of growth trade-offs. Age of sexual maturity was closely predicted by longevity in angiosperms. There was no such relationship for conifers as a whole, though there was for pines. The lack of relationship for all conifers might be explained by (i) variation in reproductive opportunities for young trees of different species, or (ii) variation in growth rates of young trees in certain adverse habitats occupied by conifers.
Article
Full-text available
1. Plant traits are fundamental for understanding and predicting vegetation responses to global changes, and they provide a promising basis towards a more quantitative and predictive approach to ecology. As a consequence, information on plant traits is rapidly accumulating, and there is a growing need for efficient database tools that enable the assembly and synthesis of trait data. 2. Plant traits are highly heterogeneous, exhibit a low degree of standardization and are linked and interdependent at various levels of biological organization: tissue, organ, plant and population. Therefore, they often require ancillary data for interpretation, including descriptors of the biotic and abiotic environment, methods and taxonomic relationships. 3. We introduce a generic database structure that is tailored to accommodate plant trait complexity and is consistent with current theoretical approaches to characterize the structure of observational data. The over-arching utility of the proposed database structure is illustrated based on two independent plant trait database projects. 4. The generic database structure proposed here is meant to serve as a flexible blueprint for future plant trait databases, improving data discovery, and ensuring compatibility among them.
Article
Full-text available
Seasonality in nitrogen (N) and phosphorus (P) concentration in soil and shoots of five Brachystegia-Julbernardia (miombo) woodland trees was studied from September 1991 to March 1993 at two regrowth miombo sites in central Zambia. Shoot growth started in the dry season (September–November) and lasted until April during the 1991/92 season but had virtually ceased by January 1993 during the 1992/93 season. The shoot growing season was associated with low foliar N/P ratios. These ratios were much lower (
Article
Full-text available
Variation in leaf life-span has long been considered of ecological significance.Despite this, quantitative evaluation of the relationships between leaf life-span and other plant and ecosystem characteristics has been rare. In this paper we ask whether leaf life-span is related to other leaf, plant, and stand traits of species from diverse ecosystems and biomes. We also examine the interaction between leaf, plant, and stand traits and their relation to productivity and ecological patterns. Among all species, both mass- (A"m"a"s"s) and area-based (A"a"r"e"a) maximum net photosynthesis decreased with increasing leaf life-span, but the relationship was stronger on a mass (P .25, r^2 = 0.01). Specific leaf area (SLA, leaf area/leaf dry mass) and leaf diffusive conductance also decreased with increasing leaf life-span. Decreasing A"m"a"s"s with increasing leaf life-span results from the impact of decreasing N"m"a"s"s and SLA on A"m"a"s"s. Variation in leaf traits as a function of leaf life-span was similar for broad-leaved and needle-leaved subsets of the data. These leaf-scale data from several biomes were compared to a data set from a single biome, Amazonia. For several leaf traits (e.g., SLA, N"m"a"s"s, and A"m"a"s"s) the quantitative relationship with leaf life-span was similar in the two independent data sets, suggesting that these are fundamental relations applicable to all species. A"m"a"s"s was a linear function of N"m"a"s"s (P .001, r^2 = 0.74) with a regression similar to previous analyses, while A"a"r"e"a was not significantly related to N"a"r"e"a. These results suggest that the photosynthesis-leaf N relationship among species should be considered universal when expressed on a mass, but not on a leaf area, basis. Relative growth rates (RGR) and leaf area ratio (LAR, the whole-plant ratio of leaf area to total dry mass) of seedlings decreased with increasing leaf life-span (P
Article
Full-text available
A prominent feature of comparative life histories in the well documented negative correlation between growth rate and life span [1,2]. Patterns of resource allocation during growth reflect life-history differences between species [1,2]. This is particularly striking in tropical forests, where tree species can differ greatly in their rates of growth and ages of maturity but still attain similar canopy sizes [3,4]. We provide a theoretical framework to relate life-history variables to rates of production partial M/partial t, where M is above ground body mass and t is time. Assuming that metabolic rate limits production as an individual grows, partial M/partial t proportional to M3/4 and incorporating interspecific variation in wood density we derive a universal growth law which quantitatively fits data for large sample of tropical tree species with diverse life histories. Combined with evolutionary life-history theory, [1] the growth law also predicts several qualitative features of tree demography and reproduction. This framework also provides a general answer to why relative growth rate 1/M(partial M/partial t) decreases with increasing plant size and varies differing allocation strategies [5-8].
Article
Full-text available
There is growing recognition that classifying terrestrial plant species on the basis of their function ( into 'functional types') rather than their higher taxonomic identity, is a promising way forward for tackling important ecological questions at the scale of ecosystems, landscapes or biomes. These questions include those on vegetation responses to and vegetation effects on, environmental changes ( e. g. changes in climate, atmospheric chemistry, land use or other disturbances). There is also growing consensus about a shortlist of plant traits that should underlie such functional plant classifications, because they have strong predictive power of important ecosystem responses to environmental change and/or they themselves have strong impacts on ecosystem processes. The most favoured traits are those that are also relatively easy and inexpensive to measure for large numbers of plant species. Large international research efforts, promoted by the IGBP-GCTE Programme, are underway to screen predominant plant species in various ecosystems and biomes worldwide for such traits. This paper provides an international methodological protocol aimed at standardising this research effort, based on consensus among a broad group of scientists in this field. It features a practical handbook with step-by-step recipes, with relatively brief information about the ecological context, for 28 functional traits recognised as critical for tackling large-scale ecological questions.
Article
Full-text available
Despite striking differences in climate, soils, and evolutionary history among diverse biomes ranging from tropical and temperate forests to alpine tundra and desert, we found similar interspecific relationships among leaf structure and function and plant growth in all biomes. Our results thus demonstrate convergent evolution and global generality in plant functioning, despite the enormous diversity of plant species and biomes. For 280 plant species from two global data sets, we found that potential carbon gain (photosynthesis) and carbon loss (respiration) increase in similar proportion with decreasing leaf life-span, increasing leaf nitrogen concentration, and increasing leaf surface area-to-mass ratio. Productivity of individual plants and of leaves in vegetation canopies also changes in constant proportion to leaf life-span and surface area-to-mass ratio. These global plant functional relationships have significant implications for global scale modeling of vegetation-atmosphere CO2 exchange.
Article
Full-text available
Leaf mass per unit area (LMA) and internal leaf anatomy often affect net gas exchange because of their effects on internal CO2 conductance to the site of carboxylation, internal shading, competition for CO2 among carboxylation sites, nitrogen concentration and its partitioning. To evaluate effects of LMA and leaf anatomy on CO2 assimilation, water-use efficiency (WUE) and nitrogen-use efficiency (NUE), we measured LMA, leaf thickness, the thickness of mesophyll components, and gas exchange rates at ambient CO2 concentration in leaves of six woody deciduous and evergreen species with different leaf life spans. In two species, CO2 assimilation was also estimated at saturating CO2 concentrations. There were interspecific differences in all morphological variables studied. Long-lived leaves had higher LMA and were thicker than short-lived leaves. Species with high LMA had low assimilation rates and NUE, both in ambient and saturating CO2 concentrations. Thus, in species with high LMA, assimilation was reduced by non-stomatal limitations, possibly because of a lower allocation of N to the photosynthetic machinery than in species with low LMA. Within a species, thicker leaves tended to have a lower tissue density. In intraspecific comparisons under field conditions, increasing internal air volume had positive effects on WUE, probably because of enhanced internal CO2 conductance to the site of carboxylation. We conclude that, in interspecific comparisons, different patterns of N partitioning strongly influence NUE, whereas in intraspecific comparisons, internal leaf anatomy is a key factor regulating resource-use efficiency.
Article
Full-text available
Functional convergence in hydraulic architecture and water relations, and potential trade-offs in resource allocation were investigated in six dominant neotropical savanna tree species from central Brazil during the peak of the dry season. Common relationships between wood density and several aspects of plant water relations and hydraulic architecture were observed. All species and individuals shared the same negative exponential relationship between sapwood saturated water content and wood density. Wood density was a good predictor of minimum (midday) leaf water potential and total daily transpiration, both of which decreased linearly with increasing wood density for all individuals and species. With respect to hydraulic architecture, specific and leaf-specific hydraulic conductivity decreased and the leaf:sapwood area ratio increased more than 5-fold as wood density increased from 0.37 to 0.71 g cm(-3) for all individuals and species. Wood density was also a good predictor of the temporal dynamics of water flow in stems, with the time of onset of sap flow in the morning and the maximum sap flow tending to occur progressively earlier in the day as wood density increased. Leaf properties associated with wood density included stomatal conductance, specific leaf area, and osmotic potential at the turgor loss point, which decreased linearly with increasing wood density. Wood density increased linearly with decreasing bulk soil water potential experienced by individual plants during the dry season, suggesting that wood density was greatest in individuals with mostly shallow roots, and therefore limited access to more abundant soil water at greater depths. Despite their taxonomic diversity and large intrapopulation differences in architectural traits, the six co-occurring species and their individuals shared similar functional relationships between all pairs of variables studied. Thus, rather than differing intrinsically in physiological responsiveness, the species and the individuals appeared to have distinct operating ranges along common physiological response curves dictated by plant architectural and structural features. The patterns of water uptake and access to soil water during the dry season appeared to be the main determinant of wood density, which constrained evolutionary options related to plant water economy and hydraulic architecture, leading to functional convergence in the neotropical savanna trees studied.
Article
Full-text available
Abscisic acid (ABA) regulates developmental processes and abiotic stress responses in plants. We recently characterized a new Arabidopsis mutant, abh1, which shows ABA-hypersensitive regulation of seed germination, stomatal closing, and cytosolic calcium increases in guard cells (V. Hugouvieux, J.M. Kwak, J.I. Schroeder [2001] Cell 106: 477-487). ABH1 encodes the large subunit of a dimeric Arabidopsis mRNA cap-binding complex and in expression profiling experiments was shown to affect mRNA levels of a subset of genes. Here, we show that the dimeric ABH1 and AtCBP20 subunits are ubiquitously expressed. Whole-plant growth phenotypes of abh1 are described and properties of ABH1 in guard cells are further analyzed. Complemented abh1 lines expressing a green fluorescent protein-ABH1 fusion protein demonstrate that ABH1 mainly localizes in guard cell nuclei. Stomatal apertures were smaller in abh1 compared with wild type (WT) when plants were grown at 40% humidity, and similar at 95% humidity. Correlated with stomatal apertures from plants grown at 40% humidity, slow anion channel currents were enhanced and inward potassium channel currents were decreased in abh1 guard cells compared with WT. Gas exchange measurements showed similar primary humidity responses in abh1 and WT, which together with results from abh1/abi1-1 double-mutant analyses suggest that abh1 shows enhanced sensitivity to endogenous ABA. Double-mutant analyses of the ABA-hypersensitive signaling mutants, era1-2 and abh1, showed complex genetic interactions, suggesting that ABH1 and ERA1 do not modulate the same negative regulator in ABA signaling. Mutations in the RNA-binding protein sad1 showed hypersensitive ABA-induced stomatal closing, whereas hyl1 did not affect this response. These data provide evidence for the model that the mRNA-processing proteins ABH1 and SAD1 function as negative regulators in guard cell ABA signaling.
Article
In southern African savannas, geoxylic suffrutices or ‘underground trees’ attain only a hundredth to a tenth the height of normal trees, but other traits have received little attention. Geoxylic suffrutices and congeneric trees were compared for minimum and maximum values of seven morphological traits. Thirty-six geoxyle-tree pairs co-occurring in Katanga (Democratic Republic of the Congo) were compared, based on data from standard floras. The tree/geoxyle ratio ranged from 0.92 to 1.67 and was greater than 1 in 12 of 14 trait comparisons. However, the difference was significant in only five comparisons. Reproductive traits generally did not differ. The maximal value of leaf traits (lamina length, lamina width, petiole length) was 33–67% greater in trees. The morphological traits of geoxyles are not much altered compared with their tree counterparts, especially for reproductive traits. For vegetative traits, geoxyles express a restricted part of the phenetic space of trees, being unable to attain trait values as high as those of their tree congeners. However, unlike bonsais or alpine dwarfs, the leaves of geoxyles are not much smaller compared with normal trees.
Article
A study of the important miombo species, Brachystegia spiciformis, B. boehmii and Julbernardia globiflora, was made for 1 year in Rhodesia in order to follow the effects of water availability and temperature on the hydrature (water content and osmotic pressure) and metabolism of these plants. Water content showed a marked initial decrease in the newly flushed leaves but then remained almost constant for the rest of the growth period, spanning both the wet and dry seasons. In contrast to this, the osmotic pressures showed a characteristic pattern of change through the year. They were low in the newly flushed leaves, increased sharply as the leaves hardened and, following the onset of the rains, they decreased to a minimum about three-quarters of the way through the season. Finally they increased again between the end of the rains and the leaf fall, but did not exceed 20 atm. Chemical analysis of the cell sap showed it to contain free and bound organic acids, mineral salts and sugars, the last of which showed a marked increase during the colder part of the growth period prior to leaf fall.
Article
Negative hydrostatic pressure can be measured in plants.
Chapter
This chapter explores some of the trade-offs and underlying constraints on stem adaptations for energy capture, and analyzes how such adaptations may limit the distribution of species along gradients, and shape the structure and physiognomy of plant communities. Such analysis provide important insights into the determinants of plant stature, crown geometry, phyllotaxis, the location of tree lines, the zonation of aquatic plants, and the shift in understory dominance from shrubs to herbs along forested gradients. The primary functions of support and competition impose four principal constraints on stem adaptations for energy capture viz. mechanical stability, mechanical safety, photosynthetic efficiency, and whole plant growth and competitive ability. Each of these constraints is discussed briefly. On the basis of this optimality criterion, the optimal form, biomechanical properties, and growth dynamics of stems in a particular ecological context should be set by five major trade-offs involving the constraints. These trade-offs involve the balance between safety vs growth and competitive ability; growth vs photosynthetic requirements; mechanical vs photosynthetic efficiency; initial vs continuing costs; and structural parasitism vs self-support. Each of these trade-offs is discussed and the resulting implications for ecological trends in stem form, resource allocation, and growth dynamics are analyzed. Context specificity is the key feature that distinguishes biomechanical ecology from pure biomechanics, and allows insights derived from functional morphology and biomechanics to illuminate ecological and evolutionary issues.
Article
In a survey on the mineral status of miombo woodland trees in Rhodesia leaves were analysed for Ca, Cl, Cu, Fe, K, Mg, Mn, Na, Ni and P. The differences among nutrients and among species illustrate differential partitioning of the nutrient pool between dominant and scattered species. In a special investigation of the seasonal variation of mineral content in the dominant miombo trees Brachystegia spiciformis, B. boehmii and Julbernardia globiflora leaves were also analysed for the same elements and also for Al and N. The elemental contents are similar for these three species. Levels of K, Mg, N and P are highest in young leaves and these elements are reabsorbed to some degree prior to abscission. Al, Ca, Fe and Mn increase with maturation of the leaves, while Cu and Zn show no regular trend of change.
Article
In forest gaps, the geometry of canopy openings above a plant determines the spatial distribution of diffuse and direct radiation, which may be received from different sectors of the sky. We examined crown orientation and light interception by seedlings of four species of pioneer trees, Cecropia obtusifolia, Heliocarpus appendiculatus, Piper auritum, and Trema micrantha, transplanted into natural forest gaps at the Los Tuxtlas Tropical Biology Station, Veracruz, Mexico. The four species differed in the number and mean size of leaves, but total leaf area was not significantly different among equal age plants. The mean azimuth and zenith angle of diffuse and direct radiation were determined from hemispherical photographs taken above each plant. Mean diffuse radiation vectors were distributed around the zenith, with a significant clustering in an easterly direction, while mean direct radiation vectors were distributed along the solar track in the southern portion of the sky. The mean orientation of the crown of each seedling was determined from detailed, three-dimensional reconstruction of leaf display using a canopy architecture model. A directional correlation test indicated that seedling crowns were orientation of individual leaves. The mechanisms of this differential response to diffuse vs. direct radiation are not known. For diffuse radiation, the total light capture capacity integrated over all sky directions increased with seedling leaf area, while efficiency of capture per unit area decreased. Based on simulations, the light interception efficiency of each plant in its own microsite was 5-25% greater than would be achieved in the sites of conspecifics of in symmetric canopy openings centered on the zenith. These analyses provide a quantitative estimate of the value of nonrandom leaf and crown orientation for whole-plant light interception in natural environments.
Article
The origin of fire-adapted lineages is a long-standing question in ecology. Although phylogeny can provide a significant contribution to the ongoing debate, its use has been precluded by the lack of comprehensive DNA data. Here, we focus on the ‘underground trees’ (=geoxyles) of southern Africa, one of the most distinctive growth forms characteristic of fire-prone savannas. We placed geoxyles within the most comprehensive dated phylogeny for the regional flora comprising over 1400 woody species. Using this phylogeny, we tested whether African geoxyles evolved concomitantly with those of the South American cerrado and used their phylogenetic position to date the appearance of humid savannas.� We found multiple independent origins of the geoxyle life-form mostly from the Pliocene, a period consistent with the origin of cerrado, with the majority of divergences occurring within the last 2 million yr. When contrasted with their tree relatives, geoxyles occur in regions characterized by higher rainfall and greater fire frequency. Our results indicate that the geoxylic growth form may have evolved in response to the interactive effects of frequent fires and high precipitation. As such, geoxyles may be regarded as markers of fire-maintained savannas occurring in climates suitable for forests.
Article
A recent controversy concerns whether plant traits that are assumed to be adaptations to fire originally evolved in response to selective factors other than fire. We contribute to this debate by investigating the evolution of the endemic woody flora of the fire-prone Cerrado of central Brazil, the most species-rich savanna in the world. We review evidence from dated phylogenies and show that Cerrado lineages started to diversify less than 10 million years ago. These Cerrado lineages are characterized by fire-resistant traits such as thick, corky bark and root sprouting, which have been considered to have evolved as adaptations to drought or nutrient-deficient soils. However, the fact that the lineages carrying these features arose coincident with the rise to dominance of flammable C4 grasses and expansion of the savanna biome worldwide, and postdating the earlier origin of seasonal climates and the nutrient-poor, acid Cerrado soils suggests that such traits should be considered as adaptations to fire regimes. The nature of these features as adaptations to fire is further suggested by their absence or poor development in related lineages found in fire-free environments with similar edaphic conditions to the Cerrado and by their repeated independent origin in diverse lineages. We present evidence to demonstrate that the evolutionary barrier to entry to the Cerrado is a weak one, presumably because of the ease of evolution of the necessary adaptations to fire regimes for lineages inhabiting neighboring fire-free biomes.
Article
We investigated functional coordination between branch hydraulic properties and leaf functional traits among nine miombo woodlands canopy tree species differing in habitat preference and phenology. Specifically, we were seeking to answer the question: are branch hydraulic properties coordinated with leaf functional traits linked to plant drought tolerance in seasonally dry tropical forests and what are the implications for species habitat preference? The hydraulic properties investigated in this study were stem area specific hydraulic conductivity (K S), Huber value (H v), and xylem cavitation vulnerability (Ψ50). The leaf functional traits measured were specific leaf area (SLA), leaf dry matter content (LDMC), and mean leaf area (MLA). Generalists displayed significantly (P < 0.05) higher cavitation resistance (Ψ50) and SLA, but lower sapwood specific hydraulic conductivity (K S), leaf specific conductivity (K L), MLA, and LDMC than mesic specialists. Although MLA was uncorrelated with Ψ50, we found significant (P < 0.05) positive and negative correlations between plant hydraulic properties and leaf functional traits linked to plant drought tolerance ability, indicating that the interactions between branch hydraulics and leaf functional traits related to plant drought tolerance ability may influence tree species habitat preference in water-limited ecosystems.
Article
The study of interspecific variation in plant ecological strategies has revealed suites of traits associated with leaf life span and with maximum levels of water deficit (measured as leaf water potentials). Here, the relationship between these sets of traits was examined in a study of 20 co-occurring chaparral shrubs that vary in leaf habit, rooting depth, and regeneration strategies. Leaf life span (LLS) and minimum seasonal water po-tentials (min) were not significantly correlated, suggesting that they are associated with independent aspects of functional variation. Multiple regression analyses of a large suite of physiological, functional, and phenological attributes in relation to these two ''anchor traits'' supported this view. Short LLS was significantly associated with high specific leaf area, high carbon assimilation and leaf nitrogen (per mass), early onset of growth, and a multistemmed, short stature growth form. This suite of traits was also associated with opportunistic regeneration following physical disturbance. Area-based gas exchange was not tightly linked to LLS. Low min (i.e., greater water deficit) was associated with high wood density, small vessel diameters, thin twigs, low leaf area : sapwood area ratios, and early onset of leaf abscission. Among the evergreen species, this suite of traits was most characteristic of post-fire seeders, which depend on high drought tolerance for post-fire regeneration of seedlings. Plant stature was the only trait associated with both the LLS axis and the min axis of functional variation. A two-dimensional strategy space, approxi-mately defined by LLS and min , can be used to distinguish contrasting strategies of drought tolerance vs. avoidance, and alternative modes of regeneration following fire and other disturbance. This conceptual scheme illustrates the strength of a trait-based approach to defining plant strategies in relation to resource availability and disturbance.
Article
The relationships between leaf structure, nitrogen concentration and CO2 assimilation rate (A) were studied for 14 grass species grown in the laboratory under non-limiting nutrient conditions. Structural features included leaf thickness and density, and the proportion of leaf volume occupied by different types of tissue (mesophyll, epidermis, vessels and sclerenchyma). Relationships were assessed for data expressed per unit leaf area and fresh mass. The latter was found to be closely related to leaf volume, which allowed us to use A per unit leaf fresh mass (Afm) as a surrogate of A per unit leaf volume. Assimilation rate per unit leaf area (Aa) was positively correlated with leaf thickness and with the amount of mesophyll per unit leaf area; the relationship with leaf nitrogen content per unit area was only marginally significant. Afm was negatively correlated with leaf thickness and positively with fresh mass-based leaf organic nitrogen concentration. A multiple regression involving these two variables explained 81% of the variance in Afm. The value of Afm was also significantly related to the proportion of mesophyll in the leaf volume, but surprisingly the correlation was negative. This was because thin leaves with high Afm and nitrogen concentration had proportionally more mechanically supportive tissues than thick ones; as a consequence, they also had a lower proportion of mesophyll. These data suggest that, in addition to leaf nitrogen, leaf thickness has a strong impact on CO2 assimilation rate for the grass species studied.
Article
1The development of simple predictors of tree growth is important in understanding forest dynamics. For this purpose, tree height, crown width in two perpendicular directions, trunk diameter at 1·3 m height (d.b.h.) and crown illumination index (CI) were determined for 727 pole-sized trees (8–20 cm d.b.h.) of 21 species, on forest dynamics plots at Pasoh Forest Reserve, Peninsular Malaysia and Lambir Hills National Park, Sarawak, Malaysia. A light-interception index (LI = AcrCI2, where Acr is crown area) was calculated for each tree, and wood density (stem wood dry mass/fresh volume) was estimated for each species from reported values.2Diameter growth rates were linearly correlated with LI (mean per species r2 = 0·45, excluding substantially damaged and vine-covered trees).3Among trees of all species, diameter growth rate was highly correlated with LI/wood density.4Mean growth rate per species varied 10-fold among the study species, but increased linearly with mean LI/wood density ratio (r2 = 0·78), consistent with the previous pattern.5Thus much of the variability in tree growth rates, both within and among species, can be accounted for by the simple mechanistic assumption that, within a given size class, growth is proportional to light interception/wood density.
Article
Assembly theory predicts that filtering processes will select species by their attributes to build a community. Some filters increase functional similarity among species, while others lead to dissimilarity. Assuming converging processes to be dominant within habitats, we tested in this study whether species assemblages across a wide range of habitats can be distinguished quantitatively by their mean trait compositions. In addition, we investigated how many and which traits are needed to describe the differences between species assemblages best. The approach has been applied on a dataset that included 12 plant traits and 7644 vegetation relevés covering a wide range of habitats in the Netherlands. We demonstrate that due to the dominant role of converging processes 1) the functional composition can explain up to 80% of the floristic differences between species assemblages using seven plant traits, showing that plant trait combinations provide a powerful tool for predicting the occurrence of species assemblages across different habitats; 2) to achieve a high performance, traits should be taken from different strategy components, i.e. traits that are functionally orthogonal, which does not necessarily coincide with low trait-trait correlations; 3) the different strategy components identified in this study correspond to the strategy components of some conventional plant ecological strategy schemes (PESS) – schemes to describe the variation between individual species. However, some PESS merge traits into one strategy component that are shown to be functionally different when predicting species assemblages. If such PESS is used to predict assemblages, this leads to a loss in predictive capacity. Potentially, our new approach is globally applicable to quantify community assembly patterns. However this needs to be tested.
Article
Summary 1. Leaf traits are commonly associated with the life history, distribution and resource requirements of a species. To improve our understanding of the ecological and physi- ological differences between tropical savanna and forest trees, we compared leaf traits of species native to savanna and gallery (riverine) forests in the Cerrado region of central Brazil. 2. Congeneric species pairs from 14 different taxonomic families were studied, each with a savanna species and a forest species present at the study site. Only individuals growing in savanna conditions under full sun were studied. We measured foliar nutrients, δ 13 C, δ 15 N and specific leaf area (SLA: leaf area per unit leaf mass). We used phylo- genetically independent contrasts to compare savanna and forest species and to test for correlations among species traits. 3. Overall, leaves of forest species had 17% higher N concentration, 32% higher P concentration, and 37% higher K concentration, despite growing in similar soils. Con- centrations of all three elements were strongly and positively correlated with SLA. 4. Forest species had 52% greater SLA, on average, than savanna species, which accounts for the higher foliar nutrient concentrations of these species. 5. Savanna species had higher δ 13 C values than forest species, indicating higher water- use efficiency. The SLA was negatively correlated with δ 13 C, suggesting that SLA may also account for the higher water-use efficiency of savanna species. 6. There was no difference in foliar δ 15 N between savanna and forest species, but foliar δ 15 N was negatively correlated with soil pH. 7. These results contribute to recent studies showing that tropical savanna and forest species represent two distinct functional types, with large differences in ecology and physiology, that have important consequences for the dynamics of savanna-forest boundaries.
Article
This book presents information about how soils provide nutrients to plants and how soils can be managed to improve their nutritional status for plant growth. The chapters are intended to help growers and agricultural extension personnel understand how soil and plant tissue analyses are interpreted to diagnose plant nutrition problems, and how soil management recommendations are developed to prevent or correct those problems. Although the details discussed are about crops and soils found in the Hawaiian Islands, the general information on soil conditions and nutrient management are applicable in many other regions of the world where the plants, soils, and climate are similar to those of Hawaii.
Article
Alfalfa was grown hydroponically in 0, 0.6, and 4.8 millimolar K in order to determine the influence of tissue level of K on photosynthesis, dark respiration, photorespiration, stomatal and mesophyll resistance to CO(2), photosystem I and II activity, and synthesis and activity of ribulose 1,5-bisphosphate carboxylase (RuBPc).A severe (0.0 millimolar) and mild (0.6 millimolar) K deficiency, compared to plants grown at 4.8 millimolar K, produced a significant decrease in photosynthesis and photorespiration, but an increase in dark respiration. Both deficient K levels increased hydrophyllic resistance to CO(2), but only the severe deficiency increased stomatal resistance.Photosystem I and II activity of isolated chloroplasts was not affected by K deficiency. The apparent activity of a crude RuBPc preparation was significantly reduced in severely deficient plants. Activity of the enzyme could not be restored to normal rates by the addition of K to the reaction medium.The specific activity of RuBPc isolated from severely K-deficient and K-sufficient leaflets was not significantly different, suggesting that K does not function in RuBPc activity. Incorporation of [(14)C]leucine into RuBPc, as a measure of synthesis, by K-deficient leaflets was reduced to 15% of K-sufficient leaflets. The addition of K to the reaction medium stimulated [(14)C]leucine incorporation into RuBPc and 10 millimolar KNO(3) increased incorporation to 80% of K-sufficient leaflets. Actinomycin D and cycloheximide suppressed the K-stimulated incorporation of [(14)C]leucine into RuBPc, suggesting that the K-stimulated synthesis of RuBPc most likely represents de novo synthesis.
Foliar analysis as a planning tool for operational fertilization
  • R P Brockley
Brockley, R.P., 2001. Foliar analysis as a planning tool for operational fertilization. In: Bamsey, C. (Ed.), Enhanced Forest Management: Fertilization and Economics Conference, March 1À2, 2001, Edmonton, AB, pp. 63-68.
The suffrutescent habit as an adaptation to environment
  • Burtt Davy
Burtt Davy, J., 1922. The suffrutescent habit as an adaptation to environment. J. Ecol. 10, 211-219. https://doi.org/10.2307/2255742.
The photosynthesisÀnitrogen relationship in wild plants
  • C Field
  • H A Mooney
Field, C., Mooney, H.A., 1986. The photosynthesisÀnitrogen relationship in wild plants. In: Givnish, T.J. (Ed.), On the Economy of Plant Form and Function. Cambridge University Press, Cambridge, pp. 25-55.
The Miombo in Transition: Woodlands and Welfare in Africa. Centre for International Forestry Research
  • P Frost
Frost, P., 1996. The ecology of miombo woodlands. In: Campbell, B. (Ed.), The Miombo in Transition: Woodlands and Welfare in Africa. Centre for International Forestry Research, Bogor, pp. 11-57. ISBN: 979-8764-07-2.
Inherent Variation in Growth Rate Between Higher Plants: A Search for Physiological Causes and Ecological Consequences
  • H Lambers
  • H Poorter
Lambers, H., Poorter, H., 2004. Inherent Variation in Growth Rate Between Higher Plants: A Search for Physiological Causes and Ecological Consequences. 34, pp. 187-261. https://doi.org/10.1016/S0065-2504(03)34004-8.
Interspecific and inter-site variation in wood specific gravity of tropical trees
  • H C Muller-Landau
Muller-Landau, H.C., 2004. Interspecific and inter-site variation in wood specific gravity of tropical trees. Biotropica 36, 20-32. https://doi.org/10.1646/02119.
Scaling maximum growth rates across photosynthetic organisms
  • S L Nielsen
  • S Enriquez
  • C M Duarte
  • K Sand-Jensen
Nielsen, S.L., Enriquez, S., Duarte, C.M., Sand-Jensen, K., 1996. Scaling maximum growth rates across photosynthetic organisms. Funct. Ecol. 10, 167-175. https://doi.org/ 10.2307/2389840. Nood en, L., 1988. The phenomena of senescence and aging. In: Nood en, D., Leopold, A.C. (Eds.), Senescence and Aging in Plants. Academic Press, London, San Diego, CA, pp. 1-50.
Leaf traits are good predictors of plant performance across 53 rain forest species
  • L Poorter
  • F Bongers
Poorter, L., Bongers, F., 2006. Leaf traits are good predictors of plant performance across 53 rain forest species. Ecology 87, 1733-1743. https://doi.org/10.1890/0012-9658 (2006)87[1733:LTAGPO]2.0.CO;2.
Cusseque -microclimate
  • R Revermann
  • M Finckh
Revermann, R., Finckh, M., 2013. Cusseque -microclimate. Biodiv. Ecol. 5, 47-50. https://doi.org/10.7809/b-e.00244.47.
Cusseque -vegetation
  • R Revermann
  • F M Gonçalves
  • A L Gomes
  • M Finckh
Revermann, R., Gonçalves, F.M., Gomes, A.L., Finckh, M., 2013. Cusseque -vegetation. Biodiv. Ecol. 5, 59-63. https://doi.org/10.7809/b-e.00247.59.
On the measurement of growth with applications to the modelling and analysis of plant growth
  • M L Roderick
Roderick, M.L., 2000. On the measurement of growth with applications to the modelling and analysis of plant growth. Funct. Ecol. 14, 244-251. https://doi.org/ 10.1093/aob/mcn050.
Wood Anatomy and Adaptation Strategies of Suffrutescent Shrubs in South-Central Angola
  • G A Sanguino Mostajo
Sanguino Mostajo, G.A., 2015. Wood Anatomy and Adaptation Strategies of Suffrutescent Shrubs in South-Central Angola. University of Hamburg.