RESUMO

Physiological information about native species, make it possible to know their potential for use in programs to recovery degraded areas. Nowadays climate changes are severe and factors as water and light are involved with plant development and growth. We hypothesized that shading may contribute to adjusting the characteristics of photosynthetic metabolism of Campomanesia xanthocarpa seedlings under flooding. Thus, this work aimed to evaluate the flooding times and shading levels for gas exchanges and the maximal photochemical efficiency of PSII (Fv/Fm) in C. xanthocarpa seedlings. Seedlings were grown under two water regimes (control and flooding), three levels of shading (0, 30, and 70%) and 4 evaluation periods (0, 15, 30, and 45 days). We verified damages to the photosynthetic apparatus and reductions in the efficiency of the photochemical process under flooding and at a high level of shading (70%) in a short period (15 days). However, seedlings showed favourable responses to the adjustment over the 45 days of exposure to those conditions. According to the multivariate analysis, it was possible to identify the relation between photosynthetic rate and stomatal conductance as the main factor of metabolic adjustments in the tolerance of C. xanthocarpa to flooding and high shading intensity. C. xanthocarpa was more sensitive to short periods of flooding conditions and full sun and high level of shading (70%), however, it presented better adjustment responses to flooding periods when associated with 30% shade.(AU)

As informações fisiológicas sobre as espécies nativas, possibilitam conhecer seu potencial para uso em programas de recuperação de áreas degradadas. As mudanças climáticas são comuns e fatores como água e luz estão envolvidos no desenvolvimento e crescimento das plantas. Nossa hipótese é que o sombreamento pode contribuir para ajustar as características do metabolismo fotossintético demudas de gabiroba-de-árvore (Campomanesia xanthocarpa) em alagamento. Assim, este trabalho teve como objetivo avaliar os tempos de alagamento e níveis de sombreamento sobre as trocas gasosas e na eficiência fotoquímica máxima do PSII (Fv/Fm) em mudas de C. xanthocarpa. As mudas foram cultivadas em dois regimes hídricos (controle e alagamento), três níveis de sombreamento (0, 30 e 70%) e quatro épocas de avaliação (0, 15, 30 e 45 dias). Verificou-se danos ao aparato fotossintético e reduções na eficiência do processo fotoquímico em alagamento e com alto nível de sombreamento (70%) por curto período (15 dias).No entanto, as mudas apresentaram respostas favoráveis de ajuste ao longo dos 45 dias de exposição nessas condições. Pela análise multivariada, foi possível identificar a relação entre a taxa fotossintética e a condutância estomática como principais fatores de ajustes metabólicos na tolerância de C. xanthocarpa ao alagamento e alta intensidade de sombreamento. C. xanthocarpa foi mais sensível nos curtos períodos de alagamento quando associada a pleno sol e ao maior sombreamento (70%). Porém, apresentou melhores respostas de ajuste aos períodos de alagamento quando associada a 30% de sombra.(AU)

Assuntos

RESUMO

Physiological information about native species, make it possible to know their potential for use in programs to recovery degraded areas. Nowadays climate changes are severe and factors as water and light are involved with plant development and growth. We hypothesized that shading may contribute to adjusting the characteristics of photosynthetic metabolism of Campomanesia xanthocarpa seedlings under flooding. Thus, this work aimed to evaluate the flooding times and shading levels for gas exchanges and the maximal photochemical efficiency of PSII (Fv/Fm) in C. xanthocarpa seedlings. Seedlings were grown under two water regimes (control and flooding), three levels of shading (0, 30, and 70%) and 4 evaluation periods (0, 15, 30, and 45 days). We verified damages to the photosynthetic apparatus and reductions in the efficiency of the photochemical process under flooding and at a high level of shading (70%) in a short period (15 days). However, seedlings showed favourable responses to the adjustment over the 45 days of exposure to those conditions. According to the multivariate analysis, it was possible to identify the relation between photosynthetic rate and stomatal conductance as the main factor of metabolic adjustments in the tolerance of C. xanthocarpa to flooding and high shading intensity. C. xanthocarpa was more sensitive to short periods of flooding conditions and full sun and high level of shading (70%), however, it presented better adjustment responses to flooding periods when associated with 30% shade.

As informações fisiológicas sobre as espécies nativas, possibilitam conhecer seu potencial para uso em programas de recuperação de áreas degradadas. As mudanças climáticas são comuns e fatores como água e luz estão envolvidos no desenvolvimento e crescimento das plantas. Nossa hipótese é que o sombreamento pode contribuir para ajustar as características do metabolismo fotossintético demudas de gabiroba-de-árvore (Campomanesia xanthocarpa) em alagamento. Assim, este trabalho teve como objetivo avaliar os tempos de alagamento e níveis de sombreamento sobre as trocas gasosas e na eficiência fotoquímica máxima do PSII (Fv/Fm) em mudas de C. xanthocarpa. As mudas foram cultivadas em dois regimes hídricos (controle e alagamento), três níveis de sombreamento (0, 30 e 70%) e quatro épocas de avaliação (0, 15, 30 e 45 dias). Verificou-se danos ao aparato fotossintético e reduções na eficiência do processo fotoquímico em alagamento e com alto nível de sombreamento (70%) por curto período (15 dias).No entanto, as mudas apresentaram respostas favoráveis de ajuste ao longo dos 45 dias de exposição nessas condições. Pela análise multivariada, foi possível identificar a relação entre a taxa fotossintética e a condutância estomática como principais fatores de ajustes metabólicos na tolerância de C. xanthocarpa ao alagamento e alta intensidade de sombreamento. C. xanthocarpa foi mais sensível nos curtos períodos de alagamento quando associada a pleno sol e ao maior sombreamento (70%). Porém, apresentou melhores respostas de ajuste aos períodos de alagamento quando associada a 30% de sombra.

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There is little information about the role of red and blue light on leaf morphology and physiology in fruit trees, and more studies have been developed in herbaceous plants grown under controlled light conditions. The objective of this research was to evaluate the effect of red and blue screens on morpho-anatomy and gas exchange in apple leaves grown under ambient sunlight conditions. Apple trees cv. Fuji were covered by 40% red and blue nets, leaving trees with 20% white net as control. Light relations (photosynthetic photon flux density, PPFD; red to far-red light ratio, R/FR and blue to red light ratio, B/R), morpho-anatomical features of the leaf (palisade to spongy mesophyll ratio, P/S, and stomata density, SD) and leaf gas exchange (net photosynthesis rate, An; stomatal conductance, g s; transpiration rate, E; and intrinsic water use efficiency, IWUE) were evaluated. Red and blue nets reduced 27% PPFD, reducing by 20% SD and 25% P/S compared to control, but without negative effects on An and g s. Blue net increased g s 21%, leading to the highest E and lowest IWUE by increment of B/R light proportion. These findings demonstrate the potential use of red and blue nets for differential modulation of apple leaf gas exchange through sunlight management under field conditions.

RESUMO

Physiological information about native species, make it possible to know their potential for use in programs to recovery degraded areas. Nowadays climate changes are severe and factors as water and light are involved with plant development and growth. We hypothesized that shading may contribute to adjusting the characteristics of photosynthetic metabolism of Campomanesia xanthocarpa seedlings under flooding. Thus, this work aimed to evaluate the flooding times and shading levels for gas exchanges and the maximal photochemical efficiency of PSII (Fv/Fm) in C. xanthocarpa seedlings. Seedlings were grown under two water regimes (control and flooding), three levels of shading (0, 30, and 70%) and 4 evaluation periods (0, 15, 30, and 45 days). We verified damages to the photosynthetic apparatus and reductions in the efficiency of the photochemical process under flooding and at a high level of shading (70%) in a short period (15 days). However, seedlings showed favourable responses to the adjustment over the 45 days of exposure to those conditions. According to the multivariate analysis, it was possible to identify the relation between photosynthetic rate and stomatal conductance as the main factor of metabolic adjustments in the tolerance of C. xanthocarpa to flooding and high shading intensity. C. xanthocarpa was more sensitive to short periods of flooding conditions and full sun and high level of shading (70%), however, it presented better adjustment responses to flooding periods when associated with 30% shade.(AU)

As informações fisiológicas sobre as espécies nativas, possibilitam conhecer seu potencial para uso em programas de recuperação de áreas degradadas. As mudanças climáticas são comuns e fatores como água e luz estão envolvidos no desenvolvimento e crescimento das plantas. Nossa hipótese é que o sombreamento pode contribuir para ajustar as características do metabolismo fotossintético de mudas de gabiroba-de-árvore (Campomanesia xanthocarpa) em alagamento. Assim, este trabalho teve como objetivo avaliar os tempos de alagamento e níveis de sombreamento sobre as trocas gasosas e na eficiência fotoquímica máxima do PSII (Fv/Fm) em mudas de C. xanthocarpa. As mudas foram cultivadas em dois regimes hídricos (controle e alagamento), três níveis de sombreamento (0, 30 e 70%) e quatro épocas de avaliação (0, 15, 30 e 45 dias). Verificou-se danos ao aparato fotossintético e reduções na eficiência do processo fotoquímico em alagamento e com alto nível de sombreamento (70%) por curto período (15 dias). No entanto, as mudas apresentaram respostas favoráveis de ajuste ao longo dos 45 dias de exposição nessas condições. Pela análise multivariada, foi possível identificar a relação entre a taxa fotossintética e a condutância estomática como principais fatores de ajustes metabólicos na tolerância de C. xanthocarpa ao alagamento e alta intensidade de sombreamento. C. xanthocarpa foi mais sensível nos curtos períodos de alagamento quando associada a pleno sol e ao maior sombreamento (70%). Porém, apresentou melhores respostas de ajuste aos períodos de alagamento quando associada a 30% de sombra.(AU)

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Climate change is expected to intensify water restriction to crops, impacting on the yield potential of crops such as popcorn. This work aimed to evaluate the performance of 10 field cultivated popcorn inbred lines during two growing seasons, under well-watered (WW) and water stressed (WS) (ψsoil≥ -1.5 MPa) conditions. Water stress was applied by withholding irrigation in the phenological phase of male pre-anthesis. Additionally, two contrasting inbred lines, P7 (superior line) and L75 (low performer) were compared for grain yield (GY) and expanded popcorn volume (EPV), selected from previous studies, were tested under greenhouse conditions. In the field, no genotype x water condition x crop season (G×WC×CS) interaction was observed, whereas GY (-51%), EPV (-55%) and leaf greenness (SPAD index) measured 17 days after anthesis (DAA) (> -10%) were highly affected by water limitation. In general, root traits (angles, number, and density) presented G×WC×CS interaction, which did not support their use as selection parameters. In relation to leaf senescence, for both WS and WW conditions, the superior inbred lines maintained a stay-green condition (higher SPAD index) until physiological maturity, but maximum SPAD index values were observed later in WW (48.7 by 14 DAA) than in WS (43.9 by 7 DAA). Under both water conditions, negative associations were observed between SPAD index values 15 and 8 days before anthesis DBA), and GY and EPV (r ≥ -0.69), as well as between SPAD index 7, 17, and 22 DAA, and angles of brace root (AB), number of crown roots (NC) and crown root density (CD), in WS (r ≥ -0.69), and AB and CD, in WW (r ≥ -0.70). Lower NC and CD values may allow further root deepening in WS conditions. Under WS P7 maintained higher net photosynthesis values, stomatal conductance, and transpiration, than L75. Additionally, L75 exhibited a lower (i.e., more negative) carbon isotope composition value than P7 under WS, confirming a lower stomatal aperture in L75. In summary, besides leaf greenness, traits related to leaf photosynthetic status, and stomatal conductance were shown to be good indicators of the agronomic performance of popcorn under water constraint.

RESUMO

The production of grafted passion fruit is an alternative for plant adaptation to saline environments. The objective of this study was to evaluate the effect of salt stress on physiology, biometry and fruit quality of P. edulis grafted on Passiflora spp. The experiment was conducted in completely randomized design, in a 3 x 2 factorial scheme, corresponding to three species of Passiflora (P. edulis, P. gibertii and P. cincinnata) with P. edulis scion and two levels of irrigation water salinity (0.5 - control and 4.5 dS m-1), with four repetitions. Water salinity compromises gas exchanges (CO2 assimilation raste and transpiration) and physiological variables (total chlorophyll and total water consumption) in grafted P. edulis. The interaction between the factors (water salinity x species) compromised only the growth in plant height and number of leaves. In relation to the species, auto-grafted P. edulis stood out from the other species, with higher internal CO2 concentration, number of leaves, stem dry mass, peel thickness, total soluble solids (TSS) of the pulp and TSS/TA ratio (titratable acidity). Auto-grafted P. edulis under saline conditions develops vital mechanisms (TSS and TSS/TA), which attenuates the effects of salt stress on the physico-chemical quality of the fruits.

A produção de maracujazeiro enxertado é uma alternativa para adaptação das plantas a ambientes salinos. Objetivou-se avaliar o efeito do estresse salino na fisiologia, biometria e qualidade de frutos de P. edulis enxertado em espécies de Passiflora spp. O delineamento utilizado foi inteiramente casualizado, em esquema fatorial 3 x 2, sendo três espécies de Passiflora (P. edulis, P. gibertii e P. cincinnata) tendo como copa P. edulis e dois níveis de salinidade de água de irrigação (0,5 ­ testemunha e 4,5 dS m-1), com quatro repetições. A salinidade da água compromete as trocas gasosas (taxa de assimilação de CO2 e transpiração) e variáveis fisiológicas (clorofila total e consumo hídrico total) em P. edulis enxertado. A interação entre os fatores (salinidade da água x espécie) compromete apenas o crescimento em altura de plantas e número de folhas. Em relação às espécies, o P. edulis auto enxertado se destaca em relação as demais espécies apresentando maior concentração interna de CO2, número de folhas, massa seca de caule, espessura da casca do fruto, sólidos solúveis totais (SST) da polpa e razão sólidos solúveis totais por acidez titulável (SST/AT). O P. edulis auto enxertado sob condições de salinidade, desenvolve mecanismos vitais (SST e SST/AT), que atenuam os efeitos do estresse salino na qualidade físico-química dos frutos.

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Microbial inoculants are suitable cost-effective technology to help plants endure drought. For the development of commercial inoculants, screening of efficient plant growth-promoting bacteria (PGPB) is a crucial step. The aim of this study was to evaluate the performance of PGPB to modulate drought resistance in Sorghum bicolor. A pot experiment with sorghum was conducted to access the role of previously selected PGPB strains. In addition, two non-inoculated control treatments (with and without urea fertilization) were also evaluated. For comparison, a fully irrigated treatment (FIT) was also assessed. All plants were fully irrigated for 47 days when the water supply was completely suspended for the drought-stressed treatments. When the soil moisture was close to zero, the irrigation was resumed. During dehydration and rehydration process, the leaf gas exchange (LGE) was evaluated. The parameters of plant growth and nitrogen nutrition were assessed 8 days after reirrigation. Comparing to the FIT, all treatments reduced the LGE rates, but in the presence of Bacillus sp. ESA 402 photosynthesis rate was less reduced. Some inoculation treatments promoted better recovery of photosynthesis, comparable to the FIT, 6 days after rehydration. The plant growth and nitrogen nutrition were negatively affected by the drought, but the inoculation of different bacteria reduced some negative effects. The nitrogen accumulation in the shoots was increased by all strains, suggesting their diazotrophic ability even under drought. Overall, the inoculation of Bacillus sp. ESA 402 was the best bacterium with potential for future field trials.

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This study aimed to evaluate the growth and physiology of Annona squamosa seedlings under increasing irrigation depths and phosphorus doses. The experiment was conducted in protected environment, evaluating five irrigation depths and four P2O5- doses, arranged in 5 x 4 factorial scheme, in randomized blocks, with four replicates and one plant per plot. Treatments were irrigation depths of 60, 80, 100, 120 and 140% of the real evapotranspiration of the seedlings ­ ETr and phosphorus doses of 0, 350, 700 and 1050 mg dm-3 of P2O5-. Plants were evaluated at 120 days after transplanting with respect to growth, gas exchanges, leaf water potential and total dry matter accumulation. Phosphorus dose of 350 mg dm-3 promotes satisfactory dry matter accumulation for A. squamosa seedlings, especially under 100% ETr irrigation. Leaf water potential and gas exchanges of A. squamosa are affected by water stress, through both lack and excess of water. Stomatal conductance is the variable most sensitive to the lack of water, whereas photosynthesis and water use efficiency are the most sensitive to the excess of water. Irrigation depth of 100% ETr is ideal to produce A. squamosa seedlings, but the irrigation depth of 80% ETr can be used to produce these seedlings, disregarding small losses of growth

Objetivou-se avaliar o crescimento e a fisiologia de mudas de A. squamosa sob lâminas crescentes de irrigação e doses de fósforo. O experimento foi conduzido em ambiente protegido, avaliando cinco lâminas de irrigação e quatro doses P2O5, arranjados em esquema fatorial 5 x 4, em blocos casualizados, com quatro repetições e uma planta por parcela. Os tratamentos das lâminas foram 60, 80, 100, 120 e 140% da evapotranspiração real das mudas ­ ETr e as quatro doses de fósforo 0, 350, 700 e 1050 mg dm-3 de P2O5. As plantas foram avaliadas aos 120 dias após o transplantio, quanto ao crescimento, trocas gasosas, potencial hídrico foliar e acúmulo de matéria seca total. A dose de fósforo de 350 mg dm-3 proporciona acúmulo de matéria seca satisfatório para as mudas de A. squamosa, principalmente sob irrigação com 100% da ETr. O potencial hídrico foliar e as trocas gasosas da A. squamosa são afetadas pelo estresse hídrico, tanto por falta como por excesso de água, sendo a condutância estomática a variável mais sensível a falta de água e a fotossíntese e eficiência do uso da água as mais sensíveis ao excesso de água. A lâmina de 100% da ETr é a ideal para a produção de mudas de A. squamosa, porém a lamina de 80% da ETr pode ser utilizada para a produção de mudas de A. squamosa, admitindo-se pequenas perdas no crescimento.

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Drought is one of the environmental factors that most affects peanut cultivation in semi-arid regions, resulting in economic losses to growers. However, growth promoting bacteria are able to reduce water deficit damage in some plant species. In this context, this study aimed to evaluate the interaction of Bradyrhizobium strains reducing water stress effects on peanut genotypes by antioxidant enzymes activities, leaf gas exchanges and vegetative growth, as well as to determine the taxonomic positioning of strain ESA 123. The 16S rRNA gene of ESA 123 was amplified by PCR and sequenced by dideoxy Sanger sequencing method. An experiment was performed in greenhouse with three peanut genotypes (BRS Havana, CNPA 76 AM and 2012-4), two Bradyrhizobium strains (SEMIA 6144 and ESA 123), a mineral source of N and an absolute control (without N) under two water regimes (with and without irrigation). Seeds of peanut were sown and the plants were grown until 30 days after emergence. On the 20th day, the water deficit plants group had their irrigation suspended for 10 days. At in silico analyzes, ESA 123 presented 98.97% similarity with the type strain of B. kavangense. Leaf gas exchange was affected by water deficit; as well as alteration of antioxidant activities and reduction of vegetative growth variables. However, some plants inoculated with SEMIA 6144 and ESA 123 strains presented lower reductions and increment of some evaluated variables, mainly the ones inoculated with the ESA 123 strain, Bradyrhizobium sp. from the semi-arid region of Northeast Brazil. This data suggests beneficial effects of the peanut-Bradyrhizobium interaction in a water stress condition, specially with the ESA 123 strain.

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ABSTRACT Schinus terebinthifolius Raddi is a tree species that can be used in the recovery of degraded areas, as it exhibits rapid growth and has a very expansive root system, facilitating water uptake from the deeper layers of the soil. The objective of this study was to evaluate photosynthesis and enzymatic activity in S. terebinthifolius seedlings under conditions of water deficit and their potential to recover following re-irrigation. The experiment was conducted in a greenhouse under a plastic covering where plants were distributed into two groups: Group 1 - control plants, where irrigation was maintained at 70% of the water retention capacity, and Group 2 - stressed plants, where irrigation was suspended until the photosynthetic rate neared zero, followed by rehydration for 12 days, then a further suspension of irrigation. At the beginning of the experiment and during the suspension of irrigation and rehydration, plants were evaluated for gas and antioxidant enzyme exchanges. Hydric stress significantly reduced photosynthesis, stomatal transpiration conductance, carboxylation efficiency of Rubisco, and the chlorophyll content of the S. terebinthifolius plants. Following rehydration, plants recovered the carboxylation efficiency of Rubisco, but not the photosynthetic rate. Antioxidant enzyme activity increased in both the aerial part and the root in response to water deficit.

RESUMO Schinus terebinthifolius Raddi é uma espécie arbórea que pode ser utilizada em recuperação de áreas degradas, sendo uma espécie de rápido crescimento com um sistema radicular bem expansivo o que facilita captar águas nas camadas mais profundas do solo. O objetivo deste trabalho foi avaliar o metabolismo fotossintético e enzimático das mudas de S. terebinthifolius sob condições de déficit hídrico e seu potencial de recuperação após a retomada de irrigação. O experimento foi realizado em casa de vegetação sob cobertura plástica onde os vasos foram distribuídos em dois lotes sendo: 1 - Controle, onde a irrigação das plantas foi mantida a 70% da capacidade de retenção de água e o lote 2 - Estresse, onde a suspensão da irrigação foi mantida até que a taxa fotossintética apresentasse níveis próximos de zero seguida de reidratação por 12 dias e nova suspensão da irrigação. No início do experimento e na suspensão da irrigação e reidratação, as plantas foram avaliadas quanto as trocas gasosas e enzimas antioxidantes. O estresse hídrico reduz significativamente a fotossíntese, a transpiração condutância estomática, a eficiência de carboxilação da rubisco e os teores de clorofila das plantas de S. terebinthifolius. As enzimas antioxidantes aumentaram tanto na parte aérea quanto na raiz em resposta ao déficit hídrico.

RESUMO

O fogo exerce um papel importante como modelador dos ecossistemas de diversas formações vegetais, especialmente o Cerrado. Sua ação induz a brotação em diversas espécies, muitas vezes formando folhas mais vigorosas e fisiologicamente mais ativas. Nesse contexto, o presente trabalho investigou o desempenho fotossintético de folhas jovens e maduras de Vochysia cinnamomea Pohl (Vochysiaceae) em resposta à ação do fogo natural sobre uma área de cerrado rupestre da Serra da Canastra, Minas Gerais, comparando-se; (1) folhas jovens de área queimada e não queimada e (2) folhas jovens e maduras de um mesmo indivíduo. Foram analisadas folhas maduras de indivíduos de área não queimada cuja brotação ocorreu anterior à queimada, e folhas jovens de indivíduos de áreas queimadas e não queimadas cuja brotação ocorreu após a passagem do fogo. Foram coletados e analisados dados relativos às taxas fotossintéticas, rendimento quântico potencial e efetivo, taxa relativa de transporte de elétrons, assimilação líquida de CO2, condutância estomática, transpiração e teores de clorofila. Não houve diferenças significativas entre as folhas jovens da área queimada e da área não queimada em relação aos processos fisiológicos testados. Desta forma não há nenhum tipo de resposta rápida em relação à passagem do fogo. Entretanto, foram encontradas diferenças significativas quando comparadas folhas jovens e maduras. É fato que folhas jovens de V. cinnamomea são estruturalmente distintas de folhas maduras, são mais suculentas e pilosas enquanto as folhas maduras são mais coriáceas, glabras e com cutícula evidente. Estas diferenças estruturais e os estágios fisiológicos de maturação distintos se refletem nas características fisiológicas estudadas nestas folhas que, quando maduras apresentam-se com menor grau de fotoinibição, maior teor de clorofilas e maior assimilação líquida de CO2.

Post-fire effect plays an important role as a modulator of plant ecosystems, especially of the Cerrado. It induces leaf sprouting in several species, often forming vigorous and more physiologically active leaves. In the present study it was investigated the photosynthetic performance of young and mature leaves of Vochysia cinnamomea Pohl (Vochysiaceae) in response to the fire action in a "cerrado rupestre" area of Serra da Canasta, Minas Gerais, comparing; (1) young leaves from fired and intact area, and (2) young and mature leaves from the same plant. Mature leaves from intact area plants which leaf sprouting occurred before fire action in the adjacent area, and young leaves from intact and fired area which leaf sprouting occurred after fire action were analyzed. Data were collected and analyzed on photosynthetic rates, potential and effective quantum yield, electron transport rate, CO2 assimilation, stomatal conductance, transpiration and chlorophyll contents. There were no significant differences between the young leaves of the burned and unburned area in relation to physiological parameters tested. Thus there is no kind of quick response in relation to fire effects. However, significant differences between young and mature leaves were found. Young leaves are structurally distinct of the mature leaves, been more succulent and pilous while mature leaves are more coriaceous, glabrous and with thicked cuticle. The structural differences between young and mature leaves are reflected in distinct physiological performance. Mature leaves present lower degree of photoinhibition, higher pigment content and CO2 assimilation.

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This study tested the hypothesis that dissipative efficiency of tropical tree species could be an ecological advantage in the forest succession process. Daily leaf gas exchanges of a pioneer species (Guazuma ulmifolia) and a late successional species (Cariniana legalis) were evaluated under well-irrigated conditions and by withholding irrigation. Analyses of network connectance (Cg) and plant autonomy (At) were carried out in order to assess metabolic network changes in response to environmental perturbation. As a global estimation of latent heat dissipation, the capacity to both maintain and cool leaf temperature in response to air temperature changes (deltaT = TºCair - TºCleaf) was evaluated. The changes observed in both the systemic parameters (Cg and At) and the physiological ones brought about by water deficit, associated with discrepant growth rates between both species, suggested that the initial formation of gap canopies composed by pioneer species could simply be a result of the higher photosynthetic rates of these species, and not necessarily because late successional species cannot cope with such a heterogeneous environment as that of a gap. Our results indicate that, in the absence of water constraints, the highest CO2 assimilation rates of pioneer species are supported by the efficiency of the whole dissipative structure, involving both degradation and dissipative processes. As a practical result, our study suggests the deltaT analysis in order to evaluate the efficiency of dissipative structures and as a aid in characterizing functional groups.

Este estudo testou a hipótese de que maior eficiência dissipativa de espécies arbóreas tropicais poderia apresentar vantagem ecológica no processo de sucessão florestal. Medidas diárias de trocas gasosas de uma espécie pioneira (Guazuma ulmifolia) e de uma espécie secundária tardia (Cariniana legalis) foram realizadas em plantas irrigadas e com deficiência hídrica. Análises da conectância da rede de trocas gasosas (Cg) e da autonomia (At) da planta em relação ao ambiente foram realizadas com o objetivo de verificar mudanças metabólicas na rede em resposta à deficiência hídrica. Como estimativa global da dissipação de calor latente, foi avaliada a capacidade de manutenção e resfriamento da temperatura foliar diante das mudanças na temperatura do ar (deltaT = TºCar - TºCfolha). As mudanças observadas nos parâmetros sistêmicos (Cg e At) e fisiológicos em resposta à perturbação ambiental, associadas à discrepante taxa de crescimento entre as espécies, sugeriram que a formação inicial do dossel de uma clareira por espécies pioneiras poderia ser resultado das maiores taxas de fotossíntese dessas espécies, e não necessariamente decorrentes do fato de as espécies secundárias tardias não suportarem o ambiente heterogêneo da clareira. Nossos resultados indicam que os maiores valores de assimilação de CO2 das espécies pioneiras são conseqüência da maior eficiência da estrutura dissipativa como um todo, envolvendo os processos de degradação e dissipação de energia, desde que não haja restrição hídrica. Como resultado prático, nosso estudo sugere a análise de deltaT para avaliar a eficiência da estrutura dissipativa e auxiliar na caracterização dos grupos funcionais.

RESUMO

This study tested the hypothesis that dissipative efficiency of tropical tree species could be an ecological advantage in the forest succession process. Daily leaf gas exchanges of a pioneer species (Guazuma ulmifolia) and a late successional species (Cariniana legalis) were evaluated under well-irrigated conditions and by withholding irrigation. Analyses of network connectance (Cg) and plant autonomy (At) were carried out in order to assess metabolic network changes in response to environmental perturbation. As a global estimation of latent heat dissipation, the capacity to both maintain and cool leaf temperature in response to air temperature changes (deltaT = TºCair - TºCleaf) was evaluated. The changes observed in both the systemic parameters (Cg and At) and the physiological ones brought about by water deficit, associated with discrepant growth rates between both species, suggested that the initial formation of gap canopies composed by pioneer species could simply be a result of the higher photosynthetic rates of these species, and not necessarily because late successional species cannot cope with such a heterogeneous environment as that of a gap. Our results indicate that, in the absence of water constraints, the highest CO2 assimilation rates of pioneer species are supported by the efficiency of the whole dissipative structure, involving both degradation and dissipative processes. As a practical result, our study suggests the deltaT analysis in order to evaluate the efficiency of dissipative structures and as a aid in characterizing functional groups.

Este estudo testou a hipótese de que maior eficiência dissipativa de espécies arbóreas tropicais poderia apresentar vantagem ecológica no processo de sucessão florestal. Medidas diárias de trocas gasosas de uma espécie pioneira (Guazuma ulmifolia) e de uma espécie secundária tardia (Cariniana legalis) foram realizadas em plantas irrigadas e com deficiência hídrica. Análises da conectância da rede de trocas gasosas (Cg) e da autonomia (At) da planta em relação ao ambiente foram realizadas com o objetivo de verificar mudanças metabólicas na rede em resposta à deficiência hídrica. Como estimativa global da dissipação de calor latente, foi avaliada a capacidade de manutenção e resfriamento da temperatura foliar diante das mudanças na temperatura do ar (deltaT = TºCar - TºCfolha). As mudanças observadas nos parâmetros sistêmicos (Cg e At) e fisiológicos em resposta à perturbação ambiental, associadas à discrepante taxa de crescimento entre as espécies, sugeriram que a formação inicial do dossel de uma clareira por espécies pioneiras poderia ser resultado das maiores taxas de fotossíntese dessas espécies, e não necessariamente decorrentes do fato de as espécies secundárias tardias não suportarem o ambiente heterogêneo da clareira. Nossos resultados indicam que os maiores valores de assimilação de CO2 das espécies pioneiras são conseqüência da maior eficiência da estrutura dissipativa como um todo, envolvendo os processos de degradação e dissipação de energia, desde que não haja restrição hídrica. Como resultado prático, nosso estudo sugere a análise de deltaT para avaliar a eficiência da estrutura dissipativa e auxiliar na caracterização dos grupos funcionais.