Ivany Ferraz Marques Valio

Germination of seeds of tropical pioneer species under controlled and natural conditions

Seed germination of eight tropical pioneer species (Cecropia hololeuca, C. pachystachya, C. glazioui, Solanum gracillimum, S. granuloso-leprosum, S. tabacifolium, Croton floribundus and Miconia chamissois) was studied. In controlled conditions, alternating temperatures were tested from 5 to 25 °C. Low Red:Far Red ratios (R:FR) were also examined. In the field, germination was evaluated in gaps and under the canopy. With the exception of Croton floribundus, all other species were photoblastic in that higher germination percentages were found under light conditions (S. tabacifolium behaved as a negative photoblastic species at some temperatures). No relationship was found between germination percentage and alternating temperature. Germination was markedly reduced under low R:FR ratios. Alternating temperature is not the main factor affecting field germination. The low R:FR ratio under the canopy seems to be the crucial factor affecting germination.

Seedling growth of fifteen Brazilian tropical tree species differing in successional status

O crescimento de plântulas de quinze especies arboreas tropicais pertencentes a diferentes estadios sucessionais foi estudado sob condicoes de campo. As plântulas foram cultivadas sob tratamentos de radiacao plena, sombreamento artificial proporcionado por telas sombrite e sombreamento natural imposto por dossel vegetal na Reserva Municipal de Santa Genebra em Campinas, SP, Brasil. A maioria das especies estudadas sobreviveu aos tratamentos de sombreamento, com marcantes alteracoes no crescimento. Reducoes de altura, numero de entrenos, massa seca, area foliar e razao raiz/parte aerea (R/PA) foram respostas frequentes ao sombreamento, assim como tambem aumentos da razao de massa foliar (RMF), razao de area foliar (RAF) e area foliar especifica (AFE). As taxas de crescimento relativo (TCRs) e as taxas de assimilacao liquida (TALs) apresentaram-se consistentemente mais baixas nos tratamentos de sombreamento. TCR se mostrou significativamente correlacionada com TAL nos tratamentos de radiacao plena e sombreamento natural e com RAF no tratamento de sombreamento artificial. O sombreamento natural teve efeitos mais severos na reducao da area foliar e da TCR. As diferencas inter-especificas nos parâmetros R/PA, RMF, AFE e RAF nao se mostraram correlacionadas com o estadio sucessional. Foi observada uma tendencia das especies de estadios iniciais de sucessao apresentarem maiores TCRs do que as especies tardias, independentemente do ambiente de luz. As especies tardias apresentaram, em relacao as iniciais, respostas menos pronunciadas ao sombreamento. As caracteristicas apresentadas pelas especies tardias podem estar associadas com tolerância a sombra, permitindo sua manutencao sob dosseis fechados por maiores periodos de tempo.

Leaf optical properties as affected by shade in saplings of six tropical tree species differing in successional status

Tree species differing in successional status may present different responses to shade. Adjustments at leaf level may affect their optical properties, leading to changes in PAR (photosynthetically active radiation) absorbance. The aim of this study was to evaluate leaf optical properties as affected by understory shade in saplings of six tropical tree species differing in successional status and degree of shade tolerance. Chlorophyll content and specific leaf area (SLA) were also evaluated. The effects of shade on leaf optical properties and chlorophyll content differed among the studied species, whereas increased SLA was a common response for all species, reflecting the occurrence of thinner leaves under shade. The three studied shade-tolerant species - Esenbeckia leiocarpa, Myroxylon peruiferum and Hymenaea courbaril - presented a greater PAR absorbance under shade. The response of the shade-intolerant species was varied. While Schizolobium parahyba also showed a greater PAR absorbance under shade, Chorisia speciosa did not alter its spectral properties and Cecropia pachystachya presented an opposite pattern, with smaller absorbance under shade. Increases in leaf chlorophyll content were significant in the shade-tolerant species, whereas they were absent or of small magnitude in the shade-intolerant ones. Although the shade-induced decrease of leaf reflectance was the only response that safely discriminated tolerant from intolerant species, the adjustments in leaf chlorophyll content and optical properties were more consistent for the tolerant species.

Effect of light and temperature on germination and early growth of Vochysia tucanorum Mart., Vochysiaceae, in cerrado and forest soil under different radiation levels

Vochysia tucanorum Mart. (Vochysiaceae) is a very widely distributed species in the cerrado and forests in Brazil, from the State of Bahia to Parana. Its seed germination was analysed under eight treatments using different conditions of light and temperature. Up to 73 days, at least ca. 93% of the seeds germinated in all treatments, except under alternating temperatures of 35°/10°C (62%). Light enhanced germination, except under constant temperature of 25°C when seeds are not photoblastic. At this temperature, the highest percentage of germination was found. Initial vegetative growth was analysed by comparing the effects of shading, by means of different percentages of full daylight (100%, 45%, 10.6%, 4.8%), and soils from cerrado and forest. During 123 days, no mortality was recorded and cotyledons persisted on the seedlings of all treatments. In general, the seedlings of V. tucanorum were found to be more or less indifferent to the soil from cerrado or forest and shading seems to promote height increment. However, total dry mass was larger under a radiation of 45% full daylight and smaller under extreme conditions (100% or 4.8% full daylight).

Seedling growth of climbing species from a southeast Brazilian tropical forest

Climbers are considered heliophytes. They are copious at the margins of forests and natural and man-made clearings. The objective of this paper was to study the initial growth of seedlings maintained under full sunlight and shaded conditions (under a vegetation canopy). The species studied were: Aristolochia galeata, Arrabidea triplinervia, Bidens brasiliensis, Canavalia parviflora, Chamissoa altissima, Cissus sicyoides, Dalechampia pentaphylla, Dicella bracteosa, Dioscorea sp., Gouania virgata, Mascagnia anisopetala, Mutisia coccinea, Oxypetalum molle, Pithecoctenium crucigerum, Rynchosia phaseoloides, Serjania multiflora and Solanum flaccidum. The initial growth of the seedlings was followed under two conditions: at the margin and under the canopy of a mesophyllous tropical forest (22° 49′55′′ S–47° 06′33′′ W). The climbers showed high rates of growth in sunlight when compared to those under canopy. Most of the species presented higher growth of the shoot than roots but in general no significative differences between root/shoot were found in both treatments. Bidens, Cissus, Mutisia and Pithecoctenium showed a very high mortality rate under canopy but, most of the studied species survived under deep shaded forest for approximately 100 days.

Reproductive phenology of bryophytes in tropical rain forests: the sexes never sleep

Abstract Events of the sexual reproductive cycle of 11 bryophyte species (mosses and liverworts with monoicous and dioicous sexual conditions) were described for two different sites (montane and sea level) of a Brazilian tropical rain forest, during a 15 month-period. The sex expression of many species was continuous over the whole period, irrespective of the seasons and the forest sites. The specific sexual conditions of dioicous species did not change, but synoicous species had strategies to increase the chances of out-crossing, bearing unisexual branches in addition to bisexual ones. The pattern of gametangia and sporophyte development was different among the species, but the same between the sites. There was a seasonal effect on the maturation of gametangia and sporophytes. Male gametangia were mostly mature by the end of the dry season. Fertilization occurred during the wettest months and sporophytes developed during the dry season, dispersal of spores mostly towards the end of the dry season. Female gametangia were receptive over the whole period, with many mature gametangia before the start of the rainy season. Male gametangia, in contrast to female, took longer to develop and aborted in high numbers. Bryophytes in tropical rain forests are favored by wet weather and mild temperatures. Similar reproductive phenological patterns were found in different habitats with minor variations.

Photosynthesis and carbon gain under contrasting light levels in seedlings of a pioneer and a climax tree from a Brazilian Semideciduous Tropical Forest

In this study we evaluated photosynthetic characteristics and patterns of biomass accumulation in seedlings of two tree species from a Semideciduous Tropical Forest of Brazil. Seedlings of Trema micrantha (L.) Blum. (pioneer) and Hymenaea courbaril (L.) var. stilbocarpa (Hayne) Lee & Langenh. (climax) were grown for 4 months under low light (LL) (5%-8% of sunlight) and high light (HL) (100% of sunlight). Under HL, T. micrantha showed higher CO2 assimilation rates (ACO2) and light saturation than H. courbaril. Under LL, ACO2 were higher in H. courbaril. Under LL, total chlorophyll and carotenoid contents per unit leaf area were higher in H. courbaril. Chlorophyll a/b ratio was higher in T. micrantha under both light regimes. ACO2 and Fv/Fm ratio at both pre-dawn and midday in H. coubaril were lower in HL indicating chronic photoinhibition. Thus, the climax species was more susceptible to photoinhibition than the pioneer. However, H. courbaril produced higher total biomass under both treatments showing high efficiency in the maintenance of a positive carbon balance. Thus, both species expressed characteristics that favor growth under conditions that resemble their natural microenvironments, but H. courbaril also grew under HL. The ecophysiological range of responses to contrasting light levels of this climax plant seems to be broader than generally observed for other rainforest climax species. We propose that this could be related to the particular spatio-temporal light regime of the semideciduous forests.

Diaspore bank of bryophytes in tropical rain forests: the importance of breeding system, phylum and microhabitat

Diaspore banks are crucial for the maintenance and resilience of plant communities, but diaspore banks of bryophytes remain poorly known, especially from tropical ecosystems. This is the first study to focus on the role of diaspore banks of bryophytes in tropical rain forests. Our aim was to test whether microhabitat (substrate type) and species traits (breeding system, phylum) are important in explaining the diaspore bank composition. Using samples cultivated in the laboratory, we assessed the number of species and shoots emerging from bark, decaying wood and soil from two sites of the Atlantic rain forest (montane and sea level) in Brazil by comparing the contribution of species by phylum (mosses, liverworts) and breeding system (monoicous, dioicous). More species emerged from bark (68) and decaying wood (55) than from soil (22). Similar numbers of species were found at both sites. Mosses were more numerous in terms of number of species and shoots, and monoicous species dominated over dioicous species. Substrate pH had only weak effects on shoot emergence. Species commonly producing sporophytes and gemmae had a high contribution to the diaspore banks. These superficial diaspore banks represented the extant vegetation rather well, but held more monoicous species (probably short-lived species) compared to dioicous ones. We propose that diaspore bank dynamics are driven by species traits and microhabitat characteristics, and that short-term diaspore banks of bryophytes in tropical rain forests contribute to fast (re)establishment of species after disturbances and during succession, particularly dioicous mosses investing in asexual reproduction and monoicous mosses investing in sexual reproduction.

Relationship between seed size and litter effects on early seedling establishment of 15 tropical tree species

A close relationship has been reported between seed size and many different plant traits such as seedling size, relative growth rate, seedling survival, distance of dispersion, colonization and density of seeds in the soil (Coomes & Grubb 2003, Jurado & Westoby 1992, Lahoreau et al. 2006, Saverimuttu & Westoby 1996, Souza & Valio 2001). Although the association of seed size and shade tolerance is unclear (Westoby et al. 1996) some authors have suggested that a larger-seeded species is better able to tolerate low light availability (Foster 1986, Foster & Janson 1985, Leishman & Westoby 1994) by producing a vigorous seedling with a higher ability to withstand predation (Armstrong & Westoby 1993, Foster 1986) and delaying the beginning of carbon fixation so as to increase survival under a canopy and under leaf litter.

Effect of fire on flowering of Lantana montevidensis Briq.

Summary Lantana montevidensis Briq. is an endemic species of the brazilian «cerrado» (savannah) that usually flowers abundantly after burning of the vegetation. Several possible effects of fire on the induction of flowering in this species were tested with no significant result. It seems that the removal of the aerial part of the plant caused by the fire is the necessary stimulus for flowering induction. Pruning the plants caused similar results.