The aim of this work was to assess the effect of leaf thickness, leaf succulence (L S ), specific leaf area (SLA), specific leaf mass (W s ) and leaf water content (LWC) on chlorophyll (Chl) meter values in six Amazonian tree species (Carapa guianensis, Ceiba pentandra, Cynometra spruceana, Pithecolobium inaequale, Scleronema micranthum and Swietenia macrophylla). We also tested the accuracy of a general calibration equation to convert Minolta Chl meter (SPAD-502) readings into absolute Chl content. On average, SPAD values (x) increased with fresh leaf thickness (FLT [µm] = 153.9 + 0.98 x, r 2 = 0.06 ** ), dry leaf thickness (DLT [µm] = 49.50 + 1.28 x, r 2 = 0.16 ** ), specific leaf mass (W s [g (DM) m -2 ] = 6.73 + 1.31 x, r 2 = 0.43 ** ), and leaf succulence (L S [g(FM)] m -2 = 94.2 + 1.58 x, r 2 = 0.19 ** ). However, a negative relationship was found between SPAD values and either specific leaf area [SLA (m 2 kg -1 ) = 35.1 -0.37 x, r 2 = 0.38 ** ] or the leaf water content (LWC [%]= 80.0 -0.42 x, r 2 = 0.58 ** ). Leaf Chl contents predicted by the general calibration equation significantly differed (p<0.01) from those estimated by species-specific calibration equations. We conclude that to improve the accuracy of the SPAD-502 leaf thickness and LWC should be taken into account when calibration equations are to be obtained to convert SPAD values into absolute Chl content.

This study was carried out in a plantation of a degraded area in Central Amazon, Brazil, in order to assess environmental light effects on leaf pigment concentrations and chlorophyll a fluorescence in mahogany (Swietenia macrophylla King) and tonka bean (Dipteryx odorata Aubl. Willd). Three-year old saplings were grown in an open site (sun) with maximum radiation of approximately 2000 mumol m-2 s-1 and under the shade of a Ochroma pyramidale (Cav. ex Lam. Urb) canopy. A leaf area index of 2.46 was optically determined for the Ochroma foliage with 13% of full sunlight (maximum radiation about 260 mumol m-2 s-1). Carotenoid and chlorophyll concentrations were spectrophotometrically determined. Initial (Fo), maximum (Fm) and variable fluorescence (Fv) were determined with a portable fluorometer. Chlorophyll concentrations (Chl a, Chl b and Chl tot) on a fresh mass basis were greater in shade leaves than in sun acclimated leaves in both species. On the other hand, when comparisons were made on a per area basis, Chl a concentrations were greater in the sun than in shade leaves of tonka bean. In contrast, Chl b concentrations were higher in the shade environment for this species. No differences were observed in Chl concentrations per unit area in mahogany leaves. Carotenoid concentrations were higher for sun-acclimated leaves of mahogany, both on a per unit area and on a fresh mass basis. In tonka bean, higher carotenoid concentrations in shade leaves were only observed on a fresh weight basis. No differences were found between environments when carotenoid concentrations were expressed as a function of leaf area. Fluorescence variables (Fo, Fm, and Fv) were greater in sun leaves than in shade leaves of mahogany. In contrast, Fv and Fm, but not Fo, values were higher in shade acclimated leaves than in full sunlight-adapted leaves of tonka bean. However, there was a higher Fv/Fm ratio value for tonka bean in sunlight environments. We conclude that these species, classified as mid and late successional species, differ markedly regarding the utilization of photosynthetic pigments, increasing either light harvesting efficiency at low irradiance or protection against photosynthetic machinery damage in higher solar radiation environments.

A bacia amazônica tem mais de seis milhões de quilômetros quadrados e abriga a maior floresta tropical do mundo, sendo particularmente importante pela sua biodiversidade e pelo seu papel na ciclagem de água e carbono. Fotossíntese, condutância estomática e fluxo de seiva de espécies florestais da Amazônia apresentam variação ao longo do dia seguindo a variação diurna observada na irradiância, temperatura e o déficit de pressão de vapor. Em decorrência da fotorrespiração, cerca de 25% do carbono fixado é retornado para a atmosfera. Os aumentos na concentração de CO2 na atmosfera previstos para as próximas décadas poderão apresentar efeito positivo na assimilação de carbono deste ecossistema florestal. Em comparação à época chuvosa, redução da umidade do solo e aumento no déficit de pressão de vapor (associado à baixa umidade do ar e alta temperatura) favorecem o fechamento dos estômatos em detrimento da fotossíntese. Desse modo, em comparação com a estação chuvosa, a fotossíntese líquida é menor no período seco. No geral, na Amazônia as árvores que atingem o dossel da floresta crescem a taxas maiores na época chuvosa. Exceto em anos de menor precipitação, o ecossistema florestal atua como sumidouro de carbono na época chuvosa. Mais estudos são necessários para determinar como e de que forma fatores específicos do ambiente físico influenciam a assimilação de carbono e o crescimento de árvores nos diversos grupos funcionais na Amazônia.

Monoculture and mixed stands of mahogany (Swietenia macrophylla King) and tonka bean (Dipteryx odorata Willd.) trees were established on degraded land in central Amazonia to compare leaf gas exchange parameters between plants grown in sunlight in an open field and in shade beneath a balsa wood (Ochroma pyramidale Cav.) canopy. Shading increased specific leaf area by about 50% in both species. Shading reduced height and diameter growth of S. macrophylla, whereas it increased these parameters for D. odorata. Light-saturated photosynthesis (Amax), stomatal conductance (gs) and transpiration (E) were higher in S. macrophylla than in D. odorata. In S. macrophylla, Amax was higher in sun leaves (12.9 +/- 0.9 micromol m-2 s-1) than in shade leaves (10.2 +/- 1.0 micromol m-2 s-1), whereas light environment had no significant effect on Amax of D. odorata. In both species, CO2-saturated photosynthesis (Apot) was higher in sun leaves (22 +/- 1.4 micromol m-2 s-1) than in shade leaves (17-20 +/- 0.8 micromol m-2 s-1). Stomatal conductance and E increased in sun leaves of S. macrophylla by 45 and 38%, respectively, whereas light environment did not affect gs and E of D. odorata. Photorespiration rates (Pr) varied from 28 to 36% of net photosynthesis (A) at ambient atmospheric CO2 concentration (Ca) but declined to around 7% of A at higher Ca. Leaf dark respiration (Rd) and the CO2 compensation point (Gamma) were lower in shade-grown plants than in open-grown plants. Compared with shade-grown plants, total nonstructural carbohydrate (TNC) concentrations increased by 56% in S. macrophylla and by 30% in D. odorata in the open field. Leaf nitrogen (NL) concentrations were higher in open-grown plants than in shade-grown plants of both species, and TNC and NL concentrations were negatively correlated (r = -0.77). High TNC accumulation in S. macrophylla in the open field suggests that photosynthesis is unlikely to be growth-limiting at this site. We conclude that photosynthetic parameters of D. odorata are less affected by light environment than those of S. macrophylla, indicating that D. odorata has lower physiological plasticity to light than S. macrophylla.

Erythrina falcata Benth. tem sido usada na recuperação de ecossistemas degradados, como planta ornamental e em sistemas agroflorestais. Entretanto, a produção de mudas por sementes é difícil. O objetivo deste trabalho foi avaliar a propagação vegetativa de E. falcata utilizando estacas caulinares provenientes de árvores adultas (estacas herbáceas, semilenhosas e de rebrota) e mudas, coletadas em quatro épocas do ano e o efeito do ácido indolbutírico (AIB) no enraizamento de estacas dessa espécie. Depois de preparadas, as estacas foram imersas em ácido indolbutírico (AIB, 0, 1,5 e 3 g L-1). O material se desenvolveu em tubetes de plástico (55 mL), em casa de vegetação climatizada, a uma temperatura de 25 a 30ºC e umidade relativa do ar acima de 80%, em substrato de vermiculita granulometria média. Maior porcentagem de enraizamento (73%), comprimento das quatro maiores raízes (46 mm) e número de raízes (6,2) foram obtidos em estacas de mudas coletadas no verão. Não houve enraizamento em estacas semilenhosas, provenientes de árvores adultas. A imersão das estacas em AIB não exerceu qualquer influência no enraizamento. As estacas de mudas coletadas no verão são as de melhor propagação vegetativa em virtude de melhor porcentagem de enraizamento e sobrevivência.

Slow stomatal oscillations (70–95 min), associated with feedback within the plant hydraulic systems, were studied in cotton (Gossypium hirsutum L.). Oscillations were only evident when the whole plant was exposed to light, and were not influenced by reductions in intercellular CO2 concentrations (Ci) in intact, attached leaves. Oscillations were synchronised among different leaves of the same plant, even when the leaf-to-air vapour pressure difference (VPD) was reduced in a cuvette enclosing one of the leaves. In the trough phase of stomatal oscillations the apparent Ci was higher than expected from the combination of the observed assimilation rate and the A(Ci) relationship measured in the absence of oscillations. Using chlorophyll fluorescence imaging we found evidence of stomatal heterogeneity in this phase. Finally, we found that stomatal oscillations appeared to be correlated with xylem embolism, with more vessels filled with gas at the peak than at the troughs of stomatal oscillations.

Stomata are turgor-operated valves that control water loss and CO 2 uptake during photosynthesis, and thereby water relation and plant biomass accumulation is closely related to stomatal functioning. The aims of this work were to document how stomata are distributed on the leaf surface and to determine if there is any significant variation in stomatal characteristics among Amazonian tree species, and finally to study the relationship between stomatal density (S D ) and tree height. Thirty five trees (>17 m tall) of different species were selected. Stomatal type, density (S D ), size (S S ) and stomatal distribution on the leaf surface were determined using nail polish imprints taken from both leaf surfaces. Irrespective of tree species, stomata were located only on the abaxial surface (hypostomaty), with large variation in both S D and S S among species. S D ranged from 110 mm -2 in Neea altissima to 846 mm -2 in Qualea acuminata. However, in most species S D ranges between 271 and 543 mm -2 , with a negative relationship between S D and S S . We also found a positive relationship between S D and tree height (r 2 = 0.14, p < 0.01), but no correlation was found between S D and leaf thickness. The most common stomatal type was anomocytic (37%), followed by paracytic (26%) and anisocytic (11%). We conclude that in Amazonian tree species, stomatal distribution on the leaf surface is a response most likely dependent on the genetic background of every species, rather than a reaction to environmental changes, and that somehow S D is influenced by environmental factors dependent on tree height. Keywords: Amazonia, hypostomatous leaves, stomatal density, stomatal length, tropical rainforest. Densidade, tamanho e distribuição estomática em 35 espécies de árvores na Amazônia Central resumoEstômatos são válvulas operadas a turgor que controlam a perda de água e a captura de CO 2 durante a fotossíntese. Assim, as relações hídricas e o acumulo de biomassa vegetal são fortemente influenciadas pelo funcionamento estomático. Os objetivos deste trabalho foram: documentar como os estômatos estão distribuídos na superfície foliar e determinar se existe variação das características estomáticas entre espécies da Amazônia, estudar a relação entre densidade estomática (S D ) e altura arbórea. Trinta e cinco árvores (>17 m de altura) de diferentes espécies foram selecionadas. Tipo de complexo estomático, S D , tamanho (S S ) e distribuição na superfície foliar foram determinados utilizando impressões de ambas as superfícies foliares com esmalte incolor. Independente da espécie, os estômatos foram encontrados apenas na superfície abaxial (hipoestomatia) com ampla variação na S D e no S S entre espécies. A densidade estomática variou de 110 mm -2 em Neea altissima a 846 mm -2 em Qualea acuminata. Entretanto, a maioria das espécies apresentou S D entre 271 e 543 mm -2 , com uma relação negativa entre S D e S S. Observou-se uma relação positiva entre S D e altura arbórea (r 2 = 0.14, p < 0.01), não havendo relação entre S D e espess...

RESUMOO potencial hídrico da folha é um dos fatores mais importantes que afetam o funcionamento dos estômatos. O objetivo deste trabalho foi avaliar o efeito da variação diurna na irradiância e déficit de pressão de vapor (DPV) na fotossíntese (A), condutância estomática (g s ) e potencial hídrico da folha (Ψ) em Carapa guianensis (Aubl.). Os dados foram coletados de 07:00 às 17:00 h. A taxa fotossintética atingiu um valor máximo (2,5 µmol m -2 s -1 ) às 10:00 h, depois declinou até atingir um mínimo de 1 µmolm -2 s -1 às 16:00 h. A condutância estomática oscilou durante o dia, de 0,04 molm -2 s -1 (ao meio dia) para 0,02 molm -2 s -1 no final da tarde. O potencial hídrico da folha foi máximo nas primeiras horas do dia (-0,3 MPa) e mínimo (-0,75 MPa) no meio da tarde (14:30 a 15:00 h). Após ter alcançado um mínimo, o Ψ aumentou até -0,64 MPa no fim da tarde. A taxa fotossintética aumentou linearmente em função do g s (P < 0,01). Também houve uma relação positiva entre Ψ e g s (P < 0,01). A taxa fotossintética declinou durante o dia após ter alcançado um pico no início da manhã, demonstrando que os fatores ambientais que afetam o Ψ têm efeito significativo na assimilação do carbono de C. guianensis. PALAVRAS-CHAVEDéficit de pressão de vapor, potencial hídrico foliar, transpiração, trocas gasosas da folha. and lower . After reaching a minimum, MPa at sunset. Photosynthetic rates increased linearly as a function of g s (P < 0.01). Also there was a positive relationship between Ψ and g s (P< 0.01). Photosynthetic rates declined during the day after reaching a peak early in the morning, which makes clear that environmental factors that influence Ψ greatly affect carbon assimilation of C. guianensis. Photosynthesis, stomatal conductance and leaf water potential in crabwood (Carapa guianensis) ABSTRACT Leaf water potential is one of the most important factors affecting stomatal functioning. The aim of this study was to assess the effect of variation in diurnal irradiance and vapour pressure deficit on photosynthesis (A), stomatal conductance (g s ) and leaf water potential (Ψ) in KEYWORDSLeaf gas exchange, leaf water potential, transpiration, vapour pressure deficit.