Respuesta fotosintética de diferentes ecotipos de fríjol a la radiación y la salinidad

The effect of radiation and salinity on photosynthesis of different ecogeographical types of Phaseolus vulgaris ‘Cargamanto’ (South American Andean) and ‘Carioca’ (Mesoamerican) were studied. Osmotic potential, sodium accumulation, parameters gas exchange, chlorophyll a fluorescence and pigments contents were determined in the leaves to bean cultivated in experiment greenhouse using nutrient solution. The covering the seedlings with a polyethylene mesh that blocks the passage of the photosynthetically active radiation (PAR) by 50% the light treatment consisted. Subsequently, the plants exposed (E) on the radiation of the greenhouse and shade plants (S) were subjected to increasing doses of 30 mM sodium chloride (NaCl) to reach concentrations of 30, 60, 90, 120 mm and other plants kept as a control treatment. Were altered the photosynthesis by the stress by NaCl and light, but the ecotype Andean presented a greater capacity to adjust to different abiotic stress factors in relation to the Mesoamerican ecotype. E and S plants showed significant differences in the parameters of gas exchange, osmotic potential and sodium concentration on conditions salinity, but E and with stress by NaCl were more contrasting variations in relation to the S. The interaction of shade and salinity presented unique responses compared with the altered produced by each factor evaluated independently. Con la finalidad de conocer el efecto de la radiación y la salinidad sobre la fotosíntesis de diferentes tipos ecogeográficos de Phaseolus vulgaris ‘cargamanto’ (andino suramericano) y ‘carioca’ (mesoamericano), se realizaron mediciones de potencial osmótico, acumulación de sodio, intercambio gaseoso, fluorescencia de la clorofila y contenido de pigmentos en hojas de fríjol cultivadas en condiciones de invernadero con solución nutritiva. El tratamiento lumínico consistió en cubrir las plántulas con una malla de polietileno que obstruye el paso de la radiación fotosintéticamente activa en 50%. Posteriormente, las plantas expuestas a las condiciones de radiación del invernadero y las plantas con sombra se sometieron a dosis crecientes de 30 mM de cloruro de sodio hasta llegar a las concentraciones de 30, 60, 90 y 120 mM, y otras quedaron como tratamiento control. El estrés salino y lumínico alteró la fotosíntesis, pero el ecotipo andino presentó una capacidad de ajuste mayor a los diferentes factores y al estrés abiótico en relación con el ecotipo mesoamericano. Las plantas expuestas y con sombra presentaron diferencias significativas en los parámetros de intercambio gaseoso, potencial osmótico y concentración de sodio en las hojas, en condiciones de estrés salino; pero en las plantas expuestas y estresadas con NaCl, las variaciones fueron más contrastantes en relación con las que se hallaban bajo sombra. La interacción de la sombra con la salinidad presentó respuestas únicas y diferenciales en comparación con las alteraciones producidas por cada factor evaluado independientemente.   

Avaliação de métodos de aplicação de H2O2 para aclimatação de plantas de girassol à salinidade

The objective of this study was to evaluate the effect of different methods of application of hydrogen peroxide (H2O2) via seed and/or via foliar in sunflower (Helianthus annuus L.) plants under salt stress. The experiment was conducted in a greenhouse, in the experimental area of the Núcleo de Engenharia de Água e Solo - UFRB. Five treatments were tested: control (absence of NaCl); salt control (presence of 100 mM NaCl); 1 mM H2O2 via seed (in presence of 100 mM NaCl); 1 mM H2O2 via foliar (in presence of 100 mM NaCl); 1 mM H2O2 via seed + 1 mM H2O2 via foliar (in presence of 100 mM NaCl). The assay was conducted in a completely randomized design with 4 replicates. The plants were maintained during a period of 20 days in a floating type hydroponic system. Salt stress affected negatively the production of leaves, stem, roots and total dry mass. Pretreatment with H2O2 application via seed and the combination via seed + foliar via were able to reduce the deleterious effects of salinity, providing higher relative biomass yields.Objetivou-se com o presente estudo avaliar o efeito de diferentes métodos de aplicação de peróxido de hidrogênio (H2O2) via semente e/ou via foliar em plantas de girassol (Helianthus annuus L.) sob estresse salino. O experimento foi conduzido em casa de vegetação, no campo experimental do Núcleo de Engenharia de Água e Solo, UFRB. Foram testados cinco tratamentos: controle (ausência de NaCl); controle salino (presença de 100 mM NaCl); 1 mM H2O2 via semente (na presença de 100 mM NaCl); 1 mM H2O2 via foliar (na presença de 100 mM NaCl); 1 mM H2O2 via semente + 1 mM H2O2 via foliar (na presença de 100 mM NaCl). O ensaio foi realizado em delineamento inteiramente casualizado, com 4 repetições. As plantas foram mantidas durante um período de 20 dias em sistema hidropônico do tipo floating. O estresse salino reduziu significativamente a produção de massa seca das folhas, caule e raízes. O pré-tratamento com aplicação de H2O2 via semente e a combinação via semente + via foliar foram capazes de reduzir os efeitos deletérios da salinidade, proporcionando maiores produções relativas da biomassa

Pervasive gaps in Amazonian ecological research

Biodiversity loss is one of the main challenges of our time,1,2 and attempts to address it require a clear un derstanding of how ecological communities respond to environmental change across time and space.3,4 While the increasing availability of global databases on ecological communities has advanced our knowledge of biodiversity sensitivity to environmental changes,5–7 vast areas of the tropics remain understudied.8–11 In the American tropics, Amazonia stands out as the world’s most diverse rainforest and the primary source of Neotropical biodiversity,12 but it remains among the least known forests in America and is often underrepre sented in biodiversity databases.13–15 To worsen this situation, human-induced modifications16,17 may elim inate pieces of the Amazon’s biodiversity puzzle before we can use them to understand how ecological com munities are responding. To increase generalization and applicability of biodiversity knowledge,18,19 it is thus crucial to reduce biases in ecological research, particularly in regions projected to face the most pronounced environmental changes. We integrate ecological community metadata of 7,694 sampling sites for multiple or ganism groups in a machine learning model framework to map the research probability across the Brazilian Amazonia, while identifying the region’s vulnerability to environmental change. 15%–18% of the most ne glected areas in ecological research are expected to experience severe climate or land use changes by 2050. This means that unless we take immediate action, we will not be able to establish their current status, much less monitor how it is changing and what is being lostinfo:eu-repo/semantics/publishedVersio

Pervasive gaps in Amazonian ecological research

Biodiversity loss is one of the main challenges of our time,1,2 and attempts to address it require a clear understanding of how ecological communities respond to environmental change across time and space.3,4 While the increasing availability of global databases on ecological communities has advanced our knowledge of biodiversity sensitivity to environmental changes,5,6,7 vast areas of the tropics remain understudied.8,9,10,11 In the American tropics, Amazonia stands out as the world's most diverse rainforest and the primary source of Neotropical biodiversity,12 but it remains among the least known forests in America and is often underrepresented in biodiversity databases.13,14,15 To worsen this situation, human-induced modifications16,17 may eliminate pieces of the Amazon's biodiversity puzzle before we can use them to understand how ecological communities are responding. To increase generalization and applicability of biodiversity knowledge,18,19 it is thus crucial to reduce biases in ecological research, particularly in regions projected to face the most pronounced environmental changes. We integrate ecological community metadata of 7,694 sampling sites for multiple organism groups in a machine learning model framework to map the research probability across the Brazilian Amazonia, while identifying the region's vulnerability to environmental change. 15%–18% of the most neglected areas in ecological research are expected to experience severe climate or land use changes by 2050. This means that unless we take immediate action, we will not be able to establish their current status, much less monitor how it is changing and what is being lost

Photosynthetic plasticity and acclimation in tropical tree species

Com objetivo de estudar a correlação entre o grau de plasticidade/aclimatação fotossintética e o estádio sucessional de espécies arbóreas tropicais, avaliaram-se (i) as alterações fisiológicas e anatômicas em plantas jovens de oito espécies arbóreas cultivadas sob condições naturais de sub-bosque e de clareira e (ii) os efeitos do incremento de radiação solar, decorrente da abertura simulada de clareiras, sobre as características fisiológicas das plantas cultivadas no sub-bosque. Para tanto, analisaram-se o curso diário das trocas gasosas e da fluorescência da clorofila a, bem como o efeito dos distintos regimes de luz sobre os parâmetros fotossintéticos e fotoquímicos, teores de pigmentos cloroplastídicos e características anatômicas quantitativas. O estudo foi realizado na Estação de Pesquisa, Treinamento e Educação Ambiental Mata do Paraíso (EPTEA Mata Paraíso) e as espécies estudadas foram: Centrolobium tomentosum, Genipa americana, Nectandra rigida, Ocotea odorifera, Platymiscium pubescens, Siparuna guianensis, Sorocea bonplandii e Spondias dulcis. De modo geral, a maioria dessas espécies foi capaz de se ajustar ao regime de luz em que ficaram expostas, com reduções na capacidade máxima fotossintética (Amax), na irradiância de saturação (IS), na taxa aparente de transporte de elétrons (ETR), no coeficiente de extinção não fotoquímica (NPQ), nas relações de clorofila a/b e de carotenóides/clorofila total e na espessura do limbo e do parênquima paliçádico em paralelo à redução na densidade luminosa. A extensão dessas alterações variou de espécie para espécie, sendo menos pronunciada nas comumente encontradas no sub-bosque. Na clareira, representantes dessas espécies também exibiram, antes do amanhecer e no decorrer do período luminoso, valores do rendimento quântico potencial (Fv/Fm) abaixo de 0,8 e, nos horários de pico de irradiância, os menores valores de rendimento quântico efetivo (ΔF/Fm ) e ETR, indicando a ocorrência de fotoinibição crônica e menor desempenho fotoquímico sob condições de maior densidade luminosa. O estudo do efeito da abertura simulada de clareira sobre as características fisiológicas das plantas do sub-bosque mostrou que as taxas fotossintéticas foram severamente reduzidas em resposta ao súbito incremento da densidade luminosa. Tal redução foi acompanhada por substancial queda na razão Fv/Fm que, por sua vez, deveu-se em grande parte a um irreversível incremento em F0, indicando a ocorrência de danos oxidativos ao complexo coletor de luz e ao centro de reação do fotossistema II. Observou-se que com a exposição prolongada à alta irradiância, a duração e a magnitude da fotoinibição variaram substancialmente entre as espécies e, em alguns casos, as plantas permaneceram cronicamente fotoinibidas. Porém, na maioria dos casos, as plantas fotoinibidas recuperaram as taxas iniciais de assimilação e, ou, exibiram significativos aumentos na Amax acompanhados de maiores IS e ETR. Os maiores aumentos em Amax foram observados em S. dulcis, seguida em ordem decrescente por G. americana, N. rigida, S. guianensis, P. pubescens, C. tomentosum, S. bonplandii e O. odorifera. Esses resultados demonstaram existir correlação entre o grau de aclimatação fotossintética e o ambiente de ocorrência natural das espécies, o qual tende ser maior naquelas encontradas em clareiras ou ambientes abertos, em relação às típicas de sub-bosque.The aim of this work was the study of the correlation between the degree of photosynthetic plasticity/acclimation and the sucessional stage of tropical tree species. In order to assess this phenomena two different evaluation approaches were used: (i) the physiological and anatomical alterations in young plants of eight tree species cultivated under natural conditions of understory, and gap and (ii) the effects of the increment on the solar radiation, due to the simulated opening of gaps, on the physiological characteristics of the plants cultivated under understory conditions. The effect of different light regimes was also evaluated. On either case the parameters analyzed were the daily courses of the gaseous exchange and the chlorophyll fluorescence, the chloroplastidic pigments content and quantitative anatomical characteristics. The research was made in the Station of Research, Training and Environmental Education Mata do Paraiso (EPTEA Mata do Paraiso) and the studied species were: Centrolobium tomentosum, Genipa americana, Nectandra rigida, Ocotea odorifera, Platymiscium pubescens, Siparuna guianensis, Sorocea bonplandii and Spondias dulcis. In general, most of these species were able to adjust to the light regime that they were exposed to. The reduction in the light density was followed by noticeable decreased in the maximum photosynthetic capacity (Amax), in the saturation irradiance (I), in the apparent electron transport rate (ETR), in the non photochemical quenching coefficient (NPQ), in the relationships between chlorophyll a/b, total carotenoids/chlorophyll and in the thickness ratio of the limbo and the palisade parenchyma. The extension of those alterations varied from species to species, being less pronounced in those commonly found on the understory. In the gap, representatives of these species also exhibited, before dawn and during the duration of the light period, values of quantum photon yield (Fv/Fm) below 0.8 and the smallest values of effective quantum yield (F/Fm') and ETR during the period of maximum irradiance, indicating the on set of chronic photoinhibition and the lower photochemical performance under high light density. The study of the effect of simulated gaps on the physiological characteristics of the understory plants revealed that the photosynthetic rate was severely reduced in response to the sudden increment of the light density. Such reduction was accompanied by a substantial fall in the Fv/Fm ratio, which was in part due to an irreversible increase on F0, indicating the occurrence of oxidative damages on the light harvest complex and on the photosystem II reaction center. It was also observed that under prolonged subjection to high irradiance, the duration and the magnitude of the photoinhibition varied substantially among the species and in some cases the plants stayed chronically photoinhibited. However, in most cases, the photoinhibited plants recovered the initial rate of assimilation and/or exhibited significant increases in Amax followed by bigger Is and ETR. The most pronounced increments in Amax were observed in S. dulcis, followed by G. americana, N. rigida, S. guianensis, P. pubescens, C. tomentosum, S. bonplandii and O. odorifera. Overall, these results demonstrated a correlation between the photosynthetic acclimatization capacity of the species and their natural occurrence in the understoty and gap condition. Nonetheless, such finding tended to be more pronounced in the species from the gap rather than the understory condition.Fundação de Amparo a Pesquisa do Estado de Minas Gerai

Phytossociology and ecological groups in a Seasonal Semideciduous Forest in Viçosa - MG

Diferentes sistemas de classificação, nem sempre baseados em critérios claros e, freqüentemente, apoiados em observações de campo, têm sido propostos na tentativa de classificar espécies arbóreas tropicais em grupos ecológicos conforme a posição que ocupam na seqüência sucessional. O presente estudo foi desenvolvido em dois trechos de floresta semidecídua, com 15 e 30 anos, localizados no município de Viçosa, MG, objetivando verificar, por meio de variações qualitativas e quantitativas das espécies arbóreas, quais e quantos são os grupos ecológicos na sucessão secundária dessa floresta. Foram demarcadas, em cada trecho, 10 parcelas de 10 m x 20 m, onde foram inventariados todos indivíduos lenhosos com circunferência à altura de 130 cm do solo maoir ou igual a 5 cm. A similaridade florística entre as parcelas foi avaliada por meio de análise de agrupamentos, utilizando-se o índice de Sørensen. Os aspectos estruturais foram avaliados por meio da distribuição de alturas e da distribuição de diâmetros, sendo traçadas retas de regressão a partir do quociente de Liocourt. Foram amostradas 67 espécies no trecho com 15 anos e 69 no trecho com 30 anos. Dentre as espécies exclusivas, 38 foram para o trecho com 15 anos e 40 para o trecho com 30 anos. A similaridade florística entre parcelas de um mesmo trecho foi considerada alta tendo sido relacionada à proximidade espacial, o que implica em históricos de perturbação e regeneração semelhantes, resultando, conseqüentemente, em composições florísticas vimais similares e mesmo estádio de sucessão secundária. Foram amostrados, nos dois trechos do fragmento, um total de 1497 indivíduos vivos e 136 mortos em pé, resultando em uma densidade absoluta estimada de 4090 indivíduos por hectare. A área basal foi de 21,21 m 2 /ha, o diâmetro médio individual foi 5,81 cm, a altura média de 5,09 m e o volume de 192,88 m 3 /ha. A estratificação vertical associada à estrutura diamétrica permitiu detectar um grupo de espécies com tendência ao declínio de suas populações e outro com tendência ao aumento populacional. A comparação dos dados de distribuição de alturas e diâmetros, além dos dados de composição de espécies, permitiu a classificação de 13 espécies como iniciais, 18 como intermediárias e sete como tardias.Several classification systems, not all based on clear criteria and frequently supported by field observations, have been proposed to classify tropical tree species in ecological groups according to the position they occupy in the succession sequence. This study was carried out in two semideciduous forest sites, 15 and 30 years old, in Viçosa, MG, to verify through qualitative and quantitative tree species variation, how many and which are the ecological groups in this forest secondary succession. In each site, ten parcels of 10 X 20m were set, where all woody individuals with circumference at 130cm from the soil larger or equal to 5cm were inventoried. Floristic similarity between parcels was evaluated through clustering analysis, using Sørensen index. Structural aspect was evaluated by height distribution and diameter distribution, tracing regression lines from Liocourt quotient. Sixty-seven species were sample in the 15 years old area, and 69 species in the 30 years old area. From the exclusive species, 38 were in the youngest and 40 were in the oldest area. Floristic similarity between parcels within an area was considered high, being related to spatial proximity, which implies in similar histories of disturbance and regeneration, and resulting consequently in similar floristic compositions and in the same secondary succession stage. In the two areas a total of 1497 alive individuals and 136 standing dead individuals, resulting in an estimated absolute density of 4090 individuals per hectare. Basal area was of 21.21 m 2 /ha, average individual diameter was 5.81 cm, average height was 5.09 m and the volume was 192.88 m 3 /ha. The vertical stratification associated to the diameter structure allowed the detection of a group of species that tended to decline their populations and another with an increasing trend. Comparisons of height and diameter distribution data, together with viiidata on species composition, allowed the classification of 13 species as initial, 18 as intermediate, and seven as later species.Coordenação de Aperfeiçoamento de Pessoal de Nível Superio