José Pires de Lemos-Filho

Plasticity and stress tolerance override local adaptation in the responses of Mediterranean holm oak seedlings to drought and cold

Plant populations of widely distributed species experience a broad range of environmental conditions that can be faced by phenotypic plasticity or ecotypic differentiation and local adaptation. The strategy chosen will determine a populations ability to respond to climate change. To explore this, we grew Quercus ilex (L.) seedlings from acorns collected at six selected populations from climatically contrasting localities and evaluated their response to drought and late season cold events. Maximum photosynthetic rate (A(max)), instantaneous water use efficiency (iWUE), and thermal tolerance to freeze and heat (estimated from chlorophyll fluorescence versus temperature curves) were measured in 5-month-old seedlings in control (no stress), drought (water-stressed), and cold (low suboptimal temperature) conditions. The observed responses were similar for the six populations: drought decreased A(max) and increased iWUE, and cold reduced A(max) and iWUE. All the seedlings maintained photosynthetic activity under adverse conditions (drought and cold), and rapidly increased their iWUE by closing stomata when exposed to drought. Heat and freeze tolerances were similarly high for seedlings from all the populations, and they were significantly increased by drought and cold, respectively; and were positively related to each other. Differences in seedling performance across populations were primarily induced by maternal effects mediated by seed size and to a lesser extent by idiosyncratic physiologic responses to drought and low temperatures. Tolerance to multiple stresses together with the capacity to physiologically acclimate to heat waves and cold snaps may allow Q. ilex to cope with the increasingly stressful conditions imposed by climate change. Lack of evidence of physiologic seedling adaptation to local climate may reflect opposing selection pressures to complex, multidimensional environmental conditions operating within the distribution range of this species.

Environmental heterogeneity and disturbance by humans control much of the tree species diversity of Atlantic montane forest fragments in SE Brazil

The effects of human impact and environmental heterogeneity on the tree species diversity were assessed in 20 fragments of tropical montane seasonal forest in southeastern Brazil. Previous surveys of the tree community, soils and topography of the fragments provided the bulk of the data. The diversity parameters used were the means of species richness, Shannon diversity (H′), and Pielou evenness (J′) obtained from “bootstrap” sub-samplings of 1,000 trees. Morphometric variables obtained for the fragments included total, edge, and inner areas. Investigation forms were used to survey the history of human interventions and prepare an impacts matrix containing scores assigned to assess the extent, severity and duration of selected impacts. Scores for overall environmental impacts were obtained from the ordination scores produced by a multivariate analysis of the impacts matrix. A multivariate analysis of the standard deviations of soil variables was used to identify the variable which contributed most to soil heterogeneity. The same procedure was repeated for the variables related to topography and ground-water regime. The three species diversity parameters were related to the proportions of edges, the overall impacts scores, and the standard deviations of two selected soil and topographic variables. The species diversity in the fragments increased with increasing heterogeneity of both soil chemical properties and topographic features, and decreased with increasing proportion of forest edges. The evenness component of species diversity also increased with increasing severity of overall environmental impacts. This probably occurred because the 20 fragments did not include highly disturbed forests in the range and the intermediate disturbance effect on species diversity was therefore detected.

Phylogeographical Structure of the Neotropical Forest Tree Hymenaea courbaril (Leguminosae: Caesalpinioideae) and Its Relationship with the Vicariant Hymenaea stigonocarpa from Cerrado

The phylogeography of Hymenaea courbaril var. stilbocarpa from Atlantic Forest and riverine forests of the Cerrado biome in central and southeastern Brazil was investigated. The data were compared with those of its congeneric Hymenaea stigonocarpa, a typical tree from savanna. In the Cerrado, H. courbaril var. stilbocarpa is found in sites contiguous with those of H. stigonocarpa, and they share common life-history attributes. The psbC/trnS3 region of the chloroplast DNA was sequenced in 149 individuals of H. courbaril var. stilbocarpa. High genetic variation was found in this species, with the identification of 18 haplotypes, similarly to what was found in H. stigonocarpa with 23 haplotypes in the same geographic region. Populations of H. courbaril var. stilbocarpa could be structured in 3 phylogeographic groups. Spatial analysis of molecular variation indicated that 46.4% of the genetic variation was due to differences among these groups. Three haplotypes were shared by H. courbaril var. stilbocarpa and H. stigonocarpa, and only 10.5% of the total genetic variation could be attributed to between-species difference. We surmise that during the glacial times, H. courbaril var. stilbocarpa populations must have gone extinct in most parts of the southern of its present-day occurrence area. After climate amelioration, these areas were probably recolonized from northern and eastern. The relatively similar phylogeographic structure of vicariant Hymenaea species suggests that they were subjected to the same impacts during the Quaternary climatic fluctuations. The sharing of haplotypes and the genetic similarity between the 2 Hymenaea species suggest the existence of ancestral polymorphism and/or hybridization.

Is the oxidative stress caused by Aspidosperma spp. galls capable of altering leaf photosynthesis

The generation of ROS (reactive oxygen species) in plant galls may induce the degradation of the membrane systems of a plant cell and increase the number of plastoglobules. This numerical increase has been related to the prevention of damage to the thylakoid systems, and to the maintenance of photosynthesis rates. To investigate this hypothesis in gall systems, a comparative study of the ultrastructure of chloroplasts in non-galled leaves and in leaf galls of A. australe and A. spruceanum was conducted. Also, the pigment composition and the photosynthetic performance as estimated by chlorophyll fluorescence measurements were evaluated. The ultrastructural analyses revealed an increase in the number and size of plastoglobules in galls of both species studied. The levels of total chlorophylls and carotenoids were lower in galls than in non-galled tissues. The chlorophyll a/b ratio did not differ between the non-galled tissues and both kinds of galls. The values of maximum electron transport rate (ETR(MAX)) were similar for all the samples. The occurrence of numerous large plastoglobules in the galled tissues seemed to be related to oxidative stress and to the recovery of the thylakoid membrane systems. The maintenance of the ETR(MAX) values indicated the existence of an efficient strategy to maintain similar photosynthetic rates in galled and non-galled tissues.

Evolution of physiological dormancy multiple times in Melastomataceae from Neotropical montane vegetation

We investigated seed dormancy among species of Melastomataceae from Neotropical montane vegetation of Brazil. Four out of 50 studied species had dormant seeds: Miconia corallina (Miconieae), Tibouchina cardinalis (Melastomeae), Comolia sertularia (Melastomeae) and Chaetostoma armatum (Microlicieae). For these four species, germinability of seeds collected in different years was always ,10% and the percentages of embryoless seeds and non-viable embryos were both insufficient to explain low or null germinability. This is the first unequivocal report of seed dormancy in tropical Melastomataceae. The production of seeds with permeable seed coats and fully developed, differentiated embryos indicates the occurrence of physiological dormancy. The reconstructed phylogenetic tree of the 50 species suggests that physiological dormancy evolved multiple times during the evolutionary history of Melastomataceae in this vegetation. Physiological dormancy evolved in species and populations associated with xeric microhabitats, where seeds are dispersed in unfavourable conditions for establishment. Therefore, droughtinduced mortality may have been a strong selective pressure favouring the evolution of physiological dormancy in Melastomataceae. We argue that dormancy may have been independently selected in other lineages of Cerrado plants colonizing xeric microhabitats and dispersing seeds at the end of the rainy season. The contributions of our data to the understanding of seed dormancy in tropical montane vegetation are discussed.

The Genus Machaerium (Leguminosae) is More Closely Related to Aeschynomene Sect. Ochopodium than to Dalbergia: Inferences from Combined Sequence Data

Abstract Phylogenetic relationships among the genera Dalbergia, Machaerium, and Aeschynomene were investigated with sequences from both the chloroplast DNA trnL intron and the nuclear ribosomal DNA ITS/5.8S region. A parsimony and Bayesian analysis of individual and combined data resolved a monophyletic Dalbergia that is sister to a clade comprising Aeschynomene sect. Ochopodium and Machaerium. Aeschynomene sect. Aeschynomene is paraphyletic with respect to genera such as Bryaspsis and Soemmeringia, which collectively are sister to the Dalbergia-Machaerium-Ochopodium clade. This study identifies the disparate lineages of the genus Aeschynomene and reveals that species with basifixed stipules (i.e., sect. Ochopodium) perhaps should be ranked as a distinct genus. Species of Ochopodium have the general lomented fruit morphology in contrast to the unique indehiscent samara fruits of Machaerium. The findings of this analysis also have some bearing at the infrageneric level. Limited sampling of Dalbergia sects. Triptolemea and Ecastaphyllum resolves them as monophyletic. In contrast, the traditional infrageneric classification of Machaerium does not show much agreement with molecular groups. Additional sampling of Aeschynomene and Machaerium species, other DNA sequences, and morphological data are needed to resolve the exact relationship of sect. Ochopodium to Machaerium, as well as validate the infrageneric classification of Machaerium.

Are seed germination and ecological breadth associated? Testing the regeneration niche hypothesis with bromeliads in a heterogeneous neotropical montane vegetation

Abstract The role of seed germination in contributing to species ecological breadth and geographic distribution is still a matter of debate. Here, we attempted to relate seed germination requirements with ecological breadth in 12 bromeliad species from heterogeneous montane vegetation in southeastern Brazil. Seeds were set to germinate under both light and dark conditions at a broad range of temperatures to determine the breadth of the germination niche. We ran a RLQ analysis based on the matrices of species occurrence, environmental parameters and germination traits and found a significant association between germination traits, and the characteristics of sites where adult plants occur. The variation of germination responses to environmental factors was not random with habitat-generalist plants having broader germination niches and habitat-specialist plants having narrower germination niches. The RLQ analysis showed that substrate moisture and light environment were the most important factors correlated with germination traits. Phylogenetic niche conservatism appears to play a role in the patterns found here, especially in the Tillandsioideae. There is an association between the regeneration niche of a species and its ecological range, and this also provides support for the idea that the regeneration niche may help assemble plant species into heterogeneous, species-rich communities.

Concordance between Phylogeographical and Biogeographical Patterns in the Brazilian Cerrado: Diversification of the Endemic Tree Dalbergia miscolobium (Fabaceae)

Few studies have addressed the phylogeography of species of the Cerrado, the largest savanna biome of South America. Here we aimed to investigate the phylogeographical structure of Dalbergia miscolobium, a widespread tree from the Cerrado, and to verify its concordance with plant phylogeographical and biogeographical patterns so far described. A total of 287 individuals from 32 populations were analyzed by sequencing the trnL intron of the chloroplast DNA and the internal transcribed spacer of the nuclear ribosomal DNA. Analysis of population structure and tests of population expansion were performed and the time of divergence of haplotypes was estimated. Twelve and 27 haplotypes were identified in the cpDNA and nrDNA data, respectively. The star-like network configuration and the mismatch distributions indicated a recent spatial and demographic expansion of the species. Consistent with previous tree phylogeographical studies of Cerrado trees, the cpDNA also suggested a recent expansion towards the southern Cerrado. The diversity of D. miscolobium was widespread but high levels of genetic diversity were found in the Central Eastern and in the southern portion of Central Western Cerrado. The combined analysis of cpDNA and nrDNA supported a phylogeographic structure into seven groups. The phylogeographical pattern showed many concordances with biogeographical and phylogeographical studies in the Cerrado, mainly with the Cerrado phytogeographic provinces superimposed to our sampling area. The data reinforced the uniqueness of Northeastern and Southeastern Cerrados and the differentiation between Eastern and Western Central Cerrados. The recent diversification of the species (estimated between the Pliocene and the Pleistocene) and the ‘genealogical concordances’ suggest that a shared and persistent pattern of species diversification might have been present in the Cerrado over time. This is the first time that an extensive ‘genealogical concordance’ between phylogeographic and phytogeographic patterns is shown for the Cerrado biome.

Seed and Seedling Ecophysiology of Neotropical Melastomataceae: Implications for Conservation and Restoration of Savannas and Rainforests1

Abstract We review the patterns of fruit maturation, dispersal, germination, seed bank formation, and seedling establishment of the Melastomataceae in two Neotropical biodiversity hotspots, the Brazilian cerrado and the Atlantic rainforest. Studies on seed biology of the Melastomataceae are relevant because this family is ubiquitous, species-rich, and dominant in these two hotspots, and its increased relative importance is anticipated under the current scenario of habitat loss and forest fragmentation. The life-history traits of this pioneer-dominated family are quite variable in terms of fruiting phenology and seedling establishment, but less so for dispersal ecology and seed germination. Our knowledge of this seed biology is used to infer on the predicted impacts of global change and forest fragmentation for tropical forest and cerrado melastomes. Species in the Melastomataceae may be key in restoration ecology, and we discuss how seed- and seedling-based restoration techniques can assist ecosystem recovery. Resumen Revisamos los patrones de maturación de frutos, dispersión, germinación, banco de semillas y establecimiento de plantas de Melastomataceae en dos hotspots debiodiversdad, el cerrado y la Mata Atlántica. Estudios de semillas de Melastomataceae son importantes porque la familia presenta alta diversidad y es dominante en un gran rango de hábitats. Además, resulta que la familia tiene prevista su importancia aumentada en escenarios de fragmentación de bosques. Las características de história de vida de esta familia de plantas pioneras es muy variable con respecto a la fenología reproductiva y establecimiento de plántulas, pero no tanto con respecto a la ecología de dispersión de semillas y germinación. La biología de semillas embasa la discusión sobre los impactos de los cambios globales y fragmentación de bosques en Melastomataceae de sabanas y bosques tropicales. Especies de Melastomataceae pueden ser claves para la ecología de la restauración y discutimos como las técnicas de restauración basadas en semillas y plántulas pueden ayudar en la restauración.

Electrolyte leakage and chlorophyll a fluorescence among castor bean cultivars under induced water deficit

We evaluated leaf fragments of three castor bean cultivars after being subjected to water stress. Leaf discs were exposed to polyethylene glycol (PEG-6000) solutions for tissue dehydration at various water potentials. After water-stress imposition, electrolyte leakage and chlorophyll a fluorescence were used jointly on the same leaf fragments cut from the same plant leaf. Furthermore, these two experimental procedures were adapted to unequivocally distinguish cultivars’ responses to water stress. Electrolyte leakage, ion efflux, membrane injury index and maximum quantum yield of photosystem II showed genotypic differences between cultivars. Despite these genotypic differences, the photosystem II electron transport rate was not significantly affected by water stress. The membrane injury shown may have been transient, probably due to a disarrangement in the phospholipid bilayer. The use of the two experimental procedures on the same leaf samples was less time-consuming and allowed for more reliable results. Furthermore, the procedures proved efficient for selection of physiological water-stress tolerance traits and could be employed in other plant experimental models.