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Summary: Hybridization is increasingly recognized as an important evolutionary process across the tree of life. In many clades, phylogenomic approaches have permitted unparalleled insight into the extent and frequency of hybridization. However, we continue to lack a deep understanding of the factors that limit and shape patterns of hybridization, especially in evolutionary radiations. In this study, we characterized patterns of introgression across Costus (Costaceae), a young evolutionary radiation of tropical understory plants that maintain widespread interfertility despite exhibiting strong prezygotic reproductive isolation.We analyzed a phylogenomic dataset of 756 genes from 54 Costus species using multiple complementary approaches – D‐statistics, gene‐tree‐based tests, and phylogenetic network analyses – to detect and characterize introgression events throughout the evolutionary history of the radiation.Our results identified a moderate number of introgression events, including a particularly ancient, well‐supported event spanning one of the deepest divergences in the clade. Most introgression events occurred between taxa or ancestral lineages that shared the same pollination syndrome (bee‐pollinated or hummingbird‐pollinated).These findings suggest that prezygotic barriers, including pollinator specialization, have been key to the balance between introgression and reproductive isolation in Costus. [ABSTRACT FROM AUTHOR]

Summary: The threat of rising global temperatures may be especially pronounced for low‐latitude, lowland plant species that have evolved under stable climatic conditions. However, little is known about how these species may acclimate to elevated temperatures. Here, we leveraged a strong, steep thermal gradient along a natural geothermal river to assess the ability of woody plants in the Amazon to acclimate to elevated air temperatures.We measured leaf traits in six common tropical woody species along the thermal gradient to investigate whether individuals of these species: acclimate their thermoregulatory traits to maintain stable leaf temperatures despite higher ambient temperatures; acclimate their photosynthetic thermal tolerances to withstand hotter leaf temperatures; and whether acclimation is sufficient to maintain stable leaf thermal safety margins (TSMs) across different growth temperatures.Individuals of three species acclimated their thermoregulatory traits, and three species increased their thermal tolerances with growth temperature. However, acclimation was generally insufficient to maintain constant TSMs. Notwithstanding, leaf health was generally consistent across growth temperatures.Acclimation in woody Amazonian plants is generally too weak to maintain TSMs at high growth temperatures, supporting previous findings that Amazonian plants will be increasingly vulnerable to thermal stress as temperatures rise. See also the Commentary on this article by Posch, 241: 1381–1383. [ABSTRACT FROM AUTHOR]

Summary: Nutrient allocation is central to understanding plant ecological strategies and forest roles in biogeochemical cycles. Thought to be mainly driven by environmental conditions, nutrient allocation to woody organs, especially to living tissues, is poorly understood.To examine the role of differences in living tissues (sapwood, SW, vs inner bark, IB), organs, ecological strategies, and environmental conditions in driving nutrient allocation and scaling in woody plants, we quantified nitrogen and phosphorus in main stems and coarse roots of 45 species from three tropical ecosystems with contrasting precipitation, fire regime, and soil nutrients.Nutrient concentration variation was mostly explained by differences between IB and SW, followed by differences between species and, in the case of phosphorus, soil nutrient availability. IB nutrient concentrations were four times those of SW, with root tissues having slightly higher concentrations than stem tissues. Scaling between IB and SW, and between stems and roots, was generally isometric. In cross‐sections, IB contributed half of total nutrients in roots and a third in stems.Our results highlight the important role of IB and SW for nutrient storage, the coordination in nutrient allocation across tissues and organs, and the need to differentiate between IB and SW to understand plant nutrient allocation. [ABSTRACT FROM AUTHOR]

Summary: Resolving the consequences of pollinator foraging behaviour for plant mating systems is a fundamental challenge in evolutionary ecology. Pollinators may adopt particular foraging tactics: complete trapline foraging (repeated movements along a fixed route), sample‐and‐shift trapline foraging (a variable route that incorporates information from previous experiences) and territorial foraging (stochastic movements within a restricted area). Studies that integrate these pollinator foraging tactics with plant mating systems are generally lacking.We investigate the consequences of particular pollinator foraging tactics for Heliconia tortuosa. We combine parentage and sibship inference analysis with simulation modelling to: estimate mating system parameters; infer the foraging tactic adopted by the pollinators; and quantify the impact of pollinator foraging tactics on mating system parameters.We found high outcrossing rates, ubiquitous multiple paternity and a pronounced departure from near‐neighbour mating. We also found that plants repeatedly receive pollen from a series of particular donors. We infer that the pollinators primarily adopt complete trapline foraging and occasionally engage in sample‐and‐shift trapline foraging. This enhances multiple paternity without a substantial increase in near‐neighbour mating.The particular pollinator foraging tactics have divergent consequences for multiple paternity and near‐neighbour mating. Thus, pollinator foraging behaviour is an important driver of the ecology and evolution of plant mating systems. [ABSTRACT FROM AUTHOR]

Image courtesy of Kenji Suetsugu (Suetsugu I et al. i , pp. 836-841). B Cover Legend b The flower of I Oxygyne shinzatoi i (Thismiaceae), a leafless, nonphotosynthetic plant in a Japanese subtropical forest. [Extracted from the article]

Summary: Florivory is an ancient interaction which has rarely been quantified due to a lack of standardized protocols, thus impairing biogeographical and phylogenetic comparisons. We created a global, continuously updated, open‐access database comprising 180 species and 64 families to compare floral damage between tropical and temperate plants, to examine the effects of plant traits on floral damage, and to explore the eco‐evolutionary dynamics of flower–florivore interactions. Flower damage is widespread across angiosperms, but was two‐fold higher in tropical vs temperate species, suggesting stronger fitness impacts in the tropics. Flowers were mostly damaged by chewers, but neither flower color nor symmetry explained differences in florivory. Herbivory and florivory levels were positively correlated within species, even though the richness of the florivore community does not affect florivory levels. We show that florivory impacts plant fitness via multiple pathways and that ignoring this interaction makes it more difficult to obtain a broad understanding of the ecology and evolution of angiosperms. Finally, we propose a standardized protocol for florivory measurements, and identify key research avenues that will help fill persistent knowledge gaps. Florivory is expected to be a central research topic in an epoch characterized by widespread decreases in insect populations that comprise both pollinators and florivores. [ABSTRACT FROM AUTHOR]

Summary: Admixture is a mechanism by which species of long‐lived plants may acquire novel alleles. However, the potential role of admixture in the origin and maintenance of tropical plant diversity is unclear. We ask whether admixture occurs in an ecologically important clade of Eschweilera (Parvifolia clade, Lecythidaceae), which includes some of the most widespread and abundant tree species in Amazonian forests.Using target capture sequencing, we conducted a detailed phylogenomic investigation of 33 species in the Parvifolia clade and investigated specific hypotheses of admixture within a robust phylogenetic framework.We found strong evidence of admixture among three ecologically dominant species, E. coriacea, E. wachenheimii and E. parviflora, but a lack of evidence for admixture among other lineages. Accepted species were largely distinguishable from one another, as was geographic structure within species.We show that hybridization may play a role in the evolution of the most widespread and ecologically variable Amazonian tree species. While admixture occurs among some species of Eschweilera, it has not led to widespread erosion of most species' genetic or morphological identities. Therefore, current morphological based species circumscriptions appear to provide a useful characterization of the clade's lineage diversity. [ABSTRACT FROM AUTHOR]

Summary: Tropisms, growth responses to environmental stimuli such as light or gravity, are spectacular examples of adaptive plant development. The plant hormone auxin serves as a major coordinative signal. The PIN auxin exporters, through their dynamic polar subcellular localizations, redirect auxin fluxes in response to environmental stimuli and the resulting auxin gradients across organs underlie differential cell elongation and bending. In this review, we discuss recent advances concerning regulations of PIN polarity during tropisms, focusing on PIN phosphorylation and trafficking. We also cover how environmental cues regulate PIN actions during tropisms, as well as the crucial role of auxin feedback on PIN polarity during bending termination. Finally, the interactions between different tropisms are reviewed to understand plant adaptive growth in the natural environment. [ABSTRACT FROM AUTHOR]

Summary: Vulnerability curves (VCs) describe the loss of hydraulic conductance against increasing xylem tension, providing valuable insights about the response of plant water transport to water stress. Techniques to construct VCs have been developed and modified continuously, but controversies continue.We compared VCs constructed using the bench‐top dehydration (BD), air‐injection‐flow (AI), pneumatic‐air‐discharge (PAD), optical (OP) and X‐ray‐computed microtomography (MicroCT) methods for tropical trees and lianas with contrasting vessel lengths.The PAD method generated highly vulnerable VCs, the AI method intermediate VCs, whereas the BD, OP and MicroCT methods produced comparable and more resistant VCs. Vessel‐length and diameter accounted for the overestimation ratio of vulnerability estimated using the AI but not the PAD method. Compared with directly measured midday embolism levels, the PAD and AI methods substantially overestimated embolism, whereas the BD, MicroCT and OP methods provided more reasonable estimations.Cut‐open vessels, uncertainties in maximum air volume estimations, sample‐length effects, tissue cracks and shrinkage together may impede the reliability of the PAD method. In conclusion, we validate the BD, OP and MicroCT methods for tropical plants, whereas the PAD and AI need further mechanistic testing. Therefore, applications of VCs in estimating plant responses to drought need to be cautious. [ABSTRACT FROM AUTHOR]

Summary: Determining where species diversify (cradles) and persist (museums) over evolutionary time is fundamental to understanding the distribution of biodiversity and for conservation prioritization. Here, we identify cradles and museums of angiosperm generic diversity across tropical Africa, one of the most biodiverse regions on Earth.Regions containing nonrandom concentrations of young (neo‐) and old (paleo‐) endemic taxa were identified using distribution data of 1719 genera combined with a newly generated time‐calibrated mega‐phylogenetic tree. We then compared the identified regions with the current network of African protected areas (PAs).At the generic level, phylogenetic diversity and endemism are mainly concentrated in the biogeographically complex region of Eastern Africa. We show that mountainous areas are centres of both neo‐ and paleo‐endemism. By contrast, the Guineo‐Congolian lowland rain forest region is characterized by widespread and old lineages. We found that the overlap between centres of phylogenetic endemism and PAs is high (> 85%).We show the vital role played by mountains acting simultaneously as cradles and museums of tropical African plant biodiversity. By contrast, lowland rainforests act mainly as museums for generic diversity. Our study shows that incorporating large‐scale taxonomically verified distribution datasets and mega‐phylogenies lead to an improved understanding of tropical plant biodiversity evolution. [ABSTRACT FROM AUTHOR]

Because of light constraints, it is expected that latitude exerts a strong influence on reciprocal exchange of resources between mycorrhizal plants and fungi, and this could have consequences on the responsiveness of plants to mycorrhizal fungi. To assess environmental filtering due to AM fungi with regards to latitude, we synthesized data from a common garden experiment on comparative mycorrhizal responsiveness of North American annual and perennial herbaceous plants (Wilson & Hartnett, [31]) with plant distribution data for the specific plants from USDA ([28]; Notes S3). When we analysed annual and perennial plants separately, we found a significant relationship only for perennials (Kendall tau was -0.32 - P = 0.004, whereas for annuals the Kendall tau was 0.03 - P = 0.87). Negative feedback within a mutualism: host-specific growth of mycorrhizal fungi reduces plant benefit. [Extracted from the article]

Summary: The interspecific range of epigenetic variation and the degree to which differences between angiosperm species are related to geography, evolutionary history, ecological settings or species‐specific traits, remain essentially unexplored. Genome‐wide global DNA cytosine methylation is a tractable 'epiphenotypic' feature suitable for exploring these relationships.Global cytosine methylation was estimated in 279 species from two distant, ecologically disparate geographical regions: Mediterranean Spain and tropical México. At each region, four distinct plant communities were analyzed.Global methylation spanned a 10‐fold range among species (4.8–42.2%). Interspecific differences were related to evolutionary trajectories, as denoted by a strong phylogenetic signal. Genomes of tropical species were on average less methylated than those of Mediterranean ones. Woody plants have genomes with lower methylation than perennial herbs, and genomes of widespread species were less methylated than those of species with restricted geographical distribution.The eight communities studied exhibited broad and overlapping interspecific variances in global cytosine methylation and only two of them differed in average methylation. Altogether, our broad taxonomic survey supported global methylation as a plant 'epiphenotypic' trait largely associated with species evolutionary history, genome size, range size and woodiness. Additional studies are required for better understanding the environmental components underlying local and geographical variation. [ABSTRACT FROM AUTHOR]

Contents Summary 366 I. Introduction 366 II. Testing ecological theory: effects of the environment on lianas 369 III. A unified explanation for liana distribution and the maintenance of liana diversity 370 IV. Testing ecological theory: effects of lianas on the environment 373 V. Theoretical effects of lianas on forest diversity 375 VI. Lianas and trophic interactions in forests 375 VII. Unresolved challenges in liana ecology 376 VIII. Conclusions 377 Acknowledgements 377 References 377 Summary: Lianas constitute a diverse polyphyletic plant group that is advancing our understanding of ecological theory. Specifically, lianas are providing new insights into the mechanisms that control plant distribution and diversity maintenance. For example, there is now evidence that a single, scalable mechanism may explain local, regional, and pan‐tropical distribution of lianas, as well as the maintenance of liana species diversity. The ability to outcompete trees under dry, stressful conditions in seasonal forests provides lianas a growth advantage that, over time, results in relatively high abundance in seasonal forests and low abundance in aseasonal forests. Lianas may also gain a similar growth advantage following disturbance, thus explaining why liana density and diversity peak following disturbance at the local, forest scale. The study of ecology, however, is more than the effect of the environment on organisms; it also includes the effects of organisms on the environment. Considerable empirical evidence now indicates that lianas substantially alter their environment by consuming resources, suppressing tree performance, and influencing emergent properties of forests, such as ecosystem functioning, plant and animal diversity, and community composition. These recent studies using lianas are transcending classical tropical ecology research and are now providing novel insights into fundamental ecological theory. [ABSTRACT FROM AUTHOR]

Contents1333I.1334II.1335III.1339IV.1344V.1347VI.134713481348References1348 Summary: The Carboniferous, the time of Earth's penultimate icehouse and widespread coal formation, was dominated by extinct lineages of early‐diverging vascular plants. Studies of nearest living relatives of key Carboniferous plants suggest that their physiologies and growth forms differed substantially from most types of modern vegetation, particularly forests. It remains a matter of debate precisely how differently and to what degree these long‐extinct plants influenced the environment. Integrating biophysical analysis of stomatal and vascular conductivity with geochemical analysis of fossilized tissues and process‐based ecosystem‐scale modeling yields a dynamic and unique perspective on these paleoforests. This integrated approach indicates that key Carboniferous plants were capable of growth and transpiration rates that approach values found in extant crown‐group angiosperms, differing greatly from comparatively modest rates found in their closest living relatives. Ecosystem modeling suggests that divergent stomatal conductance, leaf sizes and stem life span between dominant clades would have shifted the balance of soil–atmosphere water fluxes, and thus surface runoff flux, during repeated, climate‐driven, vegetation turnovers. This synthesis highlights the importance of ‘whole plant’ physiological reconstruction of extinct plants and the potential of vascular plants to have influenced the Earth system hundreds of millions of years ago through vegetation–climate feedbacks. [ABSTRACT FROM AUTHOR]

25I. 25II. 26III. 27IV. 27V. 28VI. 32VII. 33VIII. 3435References35 Summary: A fundamental premise of this review is that distinctive phylogenetic and biogeographic patterns in clades endemic to different major biomes illuminate the evolutionary process. In seasonally dry tropical forests (SDTFs), phylogenies are geographically structured and multiple individuals representing single species coalesce. This pattern of monophyletic species, coupled with their old species stem ages, is indicative of maintenance of small effective population sizes over evolutionary timescales, which suggests that SDTF is difficult to immigrate into because of persistent resident lineages adapted to a stable, seasonally dry ecology. By contrast, lack of coalescence in conspecific accessions of abundant and often widespread species is more frequent in rain forests and is likely to reflect large effective population sizes maintained over huge areas by effective seed and pollen flow. Species nonmonophyly, young species stem ages and lack of geographical structure in rain forest phylogenies may reflect more widespread disturbance by drought and landscape evolution causing resident mortality that opens up greater opportunities for immigration and speciation. We recommend full species sampling and inclusion of multiple accessions representing individual species in phylogenies to highlight nonmonophyletic species, which we predict will be frequent in rain forest and savanna, and which represent excellent case studies of incipient speciation. [ABSTRACT FROM AUTHOR]

The article presents an analysis of the photoperiodic control and daily insolation of tree development near the equator. It mentions that the annual course of tree phenology was reported as percentage of observations. It shows that flowering of tropical trees or synchronous flushing during short periods of declining or rising insolation, respectively, were observed at all tropical latitudes in several species of adult trees.

The causes of the species richness of tropical trees are poorly understood, in particular the roles of ecological factors such as soil composition. The nickel( Ni)-hyperaccumulating tree genus Geissois (Cunoniaceae) from the South-west Pacific was chosen as a model of diversification on different substrates., Here, we investigated the leaf element compositions, spatial distributions and phylogeny of all species of Geissois occurring on New Caledonia., We found that New Caledonian Geissois descended from a single colonist and diversified relatively quickly into 13 species. Species on ultramafic and nonultramafic substrates showed contrasting patterns of leaf element composition and range overlap. Those on nonultramafic substrates were largely sympatric but had distinct leaf element compositions. By contrast, species on ultramafic substrates showed similar leaf element composition, but occurred in many cases exclusively in allopatry. Further, earlier work showed that at least three out of these seven species use different molecules to bind Ni., Geissois qualifies as a cryptic adaptive radiation, and may be the first such example in a lineage of tropical forest trees. Variation in biochemical strategies for coping with both typical and adverse soil conditions may help to explain the diversification and coexistence of tropical forest trees on similar soil types. [ABSTRACT FROM AUTHOR]

1106I.1107II.1109III.1109IV.1110V.1111VI.1111VII.1113VIII.1114IX.1114X.11161117References1117 Summary: Plant pathogens affect the fitness of their hosts and maintain biodiversity. However, we lack theories to predict the type and intensity of infections in wild plants. Here we demonstrate using fungal pathogens of tropical plants that an examination of the life histories of hosts and pathogens can reveal general patterns in their interactions. Fungal infections were more commonly reported for light‐demanding than for shade‐tolerant species and for evergreen rather than for deciduous hosts. Both patterns are consistent with classical defence theory, which predicts lower resistance in fast‐growing species and suggests that the deciduous habit can reduce enemy populations. In our literature survey, necrotrophs were found mainly to infect shade‐tolerant woody species whereas biotrophs dominated in light‐demanding herbaceous hosts. Far‐red signalling and its inhibitory effects on jasmonic acid signalling are likely to explain this phenomenon. Multiple changes between the necrotrophic and the symptomless endophytic lifestyle at the ecological and evolutionary scale indicate that endophytes should be considered when trying to understand large‐scale patterns in the fungal infections of plants. Combining knowledge about the molecular mechanisms of pathogen resistance with classical defence theory enables the formulation of testable predictions concerning general patterns in the infections of wild plants by fungal pathogens. [ABSTRACT FROM AUTHOR]

•Leaf toughness is thought to enhance physical defense and leaf lifespan. Here, we evaluated the relative importance of tissue-level leaf traits vs lamina thickness, as well as their ontogenetic changes, for structure-level leaf toughness and regeneration ecology of 19 tropical tree species. •We measured the fracture toughness of the laminas and veins of sapling leaves with shearing tests, and used principal component analysis and structural equation modeling to evaluate the multivariate relationships among traits that contribute to leaf toughness and their links to ecological performance traits. •Tissue traits (density and fracture toughness of lamina and vein) were correlated positively with each other, but independent of lamina thickness. The tissue traits and lamina thickness contributed additively to the structure-level toughness (leaf mass per area and work-to-shear). Species with dense and tough leaves as saplings also had dense and tough leaves as seedlings and adults. The patterns of ontogenetic change in trait values differed between the seedling-to-sapling and sapling-to-adult transitions. •The fracture toughness and tissue density of laminas and veins, but not the lamina thickness, were correlated positively with leaf lifespan and sapling survival, and negatively with herbivory rate and sapling regeneration light requirements, indicating the importance of tissue-level leaf traits. [ABSTRACT FROM AUTHOR]

In this article, the author discusses the result of a study which examines the changing juvenile growth patterns in tropical trees. He highlights that the study found that the juvenile selection effect was not ubiquitous. He assesse that the study raised questions, such why did an extremely shade-intolerant tree species not show a juvenile selection effect and would older trees of relatively shade-tolerant species show faster growth.

• It is well known that trees adapt their supportive tissues to changes in loading conditions, yet little is known about how the vascular anatomy is modified in this process. • We investigated this by comparing more and less mechanically loaded sections in six species of tropical trees with two different rooting morphologies. We measured the strain, vessel size, frequency and area fraction and from this calculated the specific conductivity, then measured the conductivity, modulus of elasticity and yield stress. • The smallest vessels and the lowest vessel frequency were found in the parts of the trees subjected to the greatest stresses or strains. The specific conductivity varied up to two orders of magnitude between mechanically loaded and mechanically unimportant parts of the root system. • A trade-off between conductivity and stiffness or strength was revealed, which suggests that anatomical alterations occur in response to mechanical strain. By contrast, between-tree comparisons showed that average anatomical features for the whole tree seemed more closely related to their ecological strategy. [ABSTRACT FROM AUTHOR]

• Tropical trees are often excluded from dendrochronological investigations because of a lack of distinct growth ring boundaries, causing a gap in paleoclimate reconstructions from tropical regions. • The potential use of time series of vessel features (density, diameter, surface area and hydraulic conductivity) combined with spectral analysis as a proxy for environmental conditions in the mangrove Rhizophora mucronata was investigated. • Intra-annual differences in the vessel features revealed a trade-off between hydraulic efficiency (large vessels) during the rainy season and hydraulic safety (small, more numerous vessels) during the dry season. In addition to the earlywood–latewood variations, a semiannual signal was discovered in the vessel density and diameters after Fourier transformation. • The similarity in the Fourier spectra of the vessel features and the climate data, in particular mean relative humidity and precipitation, provides strong evidence for a climatic driving force for the intra-annual variability of the vessel features. The high-resolution approach used in this study, in combination with spectral analysis, may have great potential for the study of climate variability in tropical regions. New Phytologist (2005) doi: 10.1111/j.1469-8137.2005.01415.x © New Phytologist (2005) [ABSTRACT FROM AUTHOR]

[sup 13]C enrichment in emerging leaves and its effect on carbon isotopic composition (δ[sup 13]C) of mature leaves were investigated in the neotropical pioneer tree species, Cecropia longipes and Urera caracasana, in Panama. Leaves of all ages were analysed for δ[sup 13]C, gas exchange, nitrogen, and leaf mass per area. Low intercellular to atmospheric carbon dioxide (CO[sub 2]) partial pressure (Pi : Pa); and high δ[sup 13]C of CO[sub 2] in air, intrinsic water-use efficiency, internal resistance, and carboxylation capacity were discounted as causes of [sup 13]C enrichment. [sup 13]C enrichment might occur when leaf growth is from imported organic carbon but might not reflect δ[sup 13]C values at the leaf producing the carbon. Results support hypotheses that: de novo sucrose synthesis causes [sup 13]C enrichment of mobile sugars after export from source leaves; and high ratios of PEP carboxylase (PEPc): PEPc + Rubisco cause emerging leaves to be [sup 13]C enriched relative to their growth substrate. Carbon contributions of [sup 13]C-enriched early growth could yield inaccurate Pi : Pa estimates from δ[sup 13]C in mature leaves. A model estimated investment of imported organic carbon to leaf growth and improved estimates of Pi : Pa from mature leaves. With such adjustment, δ[sup 13]C analyses provide valuable information about age-related source—sink relations in leaves. [ABSTRACT FROM AUTHOR]

This light and electron microscope study of the iridescent blue leaves of the fern Teratophyllum rotundifoliatum, reveals several novel anatomical and cytological features. In this extreme shade species [0.4-(3)-4 W m-2] of lowland tropical rainforest in peninsular Malaya, the greater part of the lamina between the simple collateral vascular bundles, consists only of epidermal cells. From 4-(6.9)--12 large chloroplasts 9.4-(17.9)-27 μm in diameter are located adjacent to the inner walls of the lens-shaped upper epidermal cells. Those in the tessellated lower epidermal cells are smaller [5.0-(7.6)-19.5 μ m], much more numerous [21-(53)-83] and regularly distributed around the periphery. They are identical in size and ultrastructure to the chloroplasts in the guard cells of the stomata. Whereas the upper epidermal chloroplasts and those in the stelar tissues contain very little starch, numerous starch grains occupy up to 53.9 % of the volume of the lower epidermal chloroplasts. As in other extreme-shade plants the epidermal chloroplasts in T. rotundifoliatum contain numerous large grana, with no preferred orientation, and integranal Iamellae completely filling the stroma. The numbers of thylakoids per granum in the lower epidermal cells [9-(29.3)-84] are significantly smaller than those in the upper [22-(86)-280]. The latter appear to be the largest yet recorded in land plants and this probably accounts for the remarkably low chlorophyll a: b ratio (1.8) in T. rotundifoliatum. Record amounts of chlorophyll per unit leaf fresh weight and per unit leaf area in T. rotundifoliatum reflect the high proportion of leaf cells containing chloroplasts. The unusual features of leaf anatomy and cytology in T. rotundifoliatum appear to be associated with maximizing the efficiency of absorption of very low diffuse radiation. [ABSTRACT FROM AUTHOR]

We examine the relationship of seed oxygen consumption rate (&Vdot;O2) to seed moisture content, seed mass, and seed age in 22 ecologically diverse tropical species. These seeds vary greatly in moisture content, age, mass, mechanism of dormancy and length of viability. We quantify each relationship with a power equation,&Vdot;O2 = αXb, where X is the independent variable. Seed moisture content (MC) explains 80 % of the variation in mass-specific &Vdot;O2 (ml O2 g-1 h-1 ) among seeds of all species, whereas seed mass explains < 1 %. However, when seeds are reclassified as moist (> 28 % MC) or dry (&les; 28 % MC), seed mass explains 54 % of the variation in mass-specific &Vdot;O2 (ml O2 g-1 h-1) within dry seeds, but no significant variation within moist seeds. In dry seeds, seed age explains only 27 % of the variance in mass-specific &Vdot;O2, although seed age and moisture content are negatively correlated. On a per seed basis, seed mass explains 56 % of the variation in &Vdot;O2 (ml O2 h-1 per seed) in dry seeds and 83 % of the variation in moist seeds: the exponents of the power function, 0·54 in dry seeds and 0·78 in moist seeds, are within the range reported for the allometric relationship of oxygen consumption and body size in animals and prokaryotes. We present a framework for future studies that recognizes seed respiration as an important, yet unstudied, component of tropical seed ecophysiology. We discuss the ecological significance of seed respiration in three groups of tropical species which differ in seed moisture content, mass, viability. [ABSTRACT FROM AUTHOR]

Summary: Little is known of the mechanisms governing nitrogen metabolism and stress tolerance in woody plants of subtropical southeast African savannas, although many of the more widely occurring genera, particularly Acacia and Combretum species, include valuable multi‐purpose trees. Basal nitrate reductase activities in vigorous leaves from 59 species and five savanna areas were used as a measure of nitrate availability. Consistently low activities were found in many of the legumes and in members of the Combretaceae. When shoots from 35 of these same species were provided with supplementary nitrate solution, increased reductase activity was recorded in a number of taxa, including non‐nodulating legumes belonging to the Caesalpinioideae. Nodulating legumes did not behave in the same way. Either proline or quaternary ammonium compounds, examples of stress metabolites, accumulated in the shoots of a range of taxa belonging to a number of families. The highest concentrations occurred in shoots collected from the driest areas. Amounts of tannin were high in some species but showed no consistent pattern. [ABSTRACT FROM AUTHOR]

The author comments on a paper by Watkins et al on tropical fern gametophytes. He believes that bryophytes are clearly not an evolutionary backwater or evolutionarily unsuccessful at their scale. He argues that the humidity measures most useful in calculating the rate of water loss from leaves are not the most relevant to evaluating the rate of water loss from poikilohydric plants.