Parâmetros fotossintéticos e crescimento em mudas de bertholletia excelsa e carapa guianensis em resposta a pré-aclimatação a pleno sol e estresse hídrico moderado

Light and water are important factors that may limit the growth and development of higher plants. The aim of this study was to evaluate photosynthetic parameters and growth in seedlings of Bertholletia excelsa and Carapa guianensis in response to pre-acclimation to full sunlight and mild water stress. I used six independent pre-acclimation treatments (0, 90 (11h15-12h45), 180 (10h30-13h30), 360 (09h00-15h00), 540 (07h30-16h30) and 720 min (06h00-18h00)) varying the time of exposure to full sunlight (PFS) during 30 days, followed by whole-day outdoor exposure for 120 days. Before PFS, the plants were kept in a greenhouse at low light levels (0.8 mol m-2 day-1). The PFS of 0 min corresponded to plants constantly kept under greenhouse conditions. From the beginning to the end of the experiment, each PFS treatment was submitted to two water regimesmoderate water stress (MWS, pre-dawn leaf water potential (ΨL) of -500 to -700 kPa) and without water stress (WWS, ΨL of -300 kPa, soil kept at field capacity). Plants under MWS received only a fraction of the amount of water applied to the well-watered ones. At the end of the 120-day-period under outdoor conditions, I evaluated light saturated photosynthesis (Amax), stomatal conductance (g s), transpiration (E) and plant growth. Both Amax and g s were higher for all plants under the PFS treatment. Stem diameter growth rate and Amax were higher for C. guianensis subjected to MWS than in well-watered plants. The contrary was true for B. excelsa. The growth of seedlings was enhanced by exposure to full sunlight for 180 minutes in both species. However, plants of B. excelsa were sensitive to moderate water stress. The higher photosynthetic rates and faster growth of C. guianensis under full sun and moderate water stress make this species a promissory candidate to be tested in reforestation programs.A luz e a água são importantes fatores que limitam o crescimento e o desenvolvimento das plantas. O objetivo deste estudo foi avaliar os paâmetros fotossintéticos e o crescimento em mudas de Bertholletia excelsa e Carapa guianensis em resposta a pré-aclimatação à luz solar plena e estresse hídrico moderado. Foram usados seis independentes tratamentos de pré-aclimatação a pleno sol (PFS), sendo estes de (0, 90 (11h15-12h45), 180 (10h30-13h30), 360 (09h00-15h00), 540 (07h30-16h30) e 720 min (06h00-18h00)) durante 30 dias seguidos por um período de exposição a pleno sol de 120 dias durante o dia todo. Antes da PFS, as plantas foram mantidas em casa de vegetação a baixos níveis de luz (0,8 mol m-2 dia-1). O PFS de 0 min correspondeu às plantas mantidas constatemente na casa de vegetação. Cada tratamento de PFS foi submetido desde o início até o final do experimento a dois regimes hídricos, denominado de estresse hídrico moderado (MWS, potencial hidrico da folha medido antes do amanhecer (ΨL) de -500 a -700 kPa) e sem estresse hídrico (WWS , ΨL de -300 kPa, solo mantido na capacidade de campo). As plantas do tratamento MWS receberam apenas uma fração do volume de água fornecido para aquelas do tratamento WWS. No final do período de 120 dias foi avaliada a fotossíntese saturada por luz (Amax), a condutância estomática (g s), transpiração (E) e o crescimento. Amax e g s foram maiores em todas as plantas sob o tratamento de PFS. A taxa de crescimento em diâmetro e Amax foram maiores em plantas de C. guianensis submetidas à MWS. O contrário foi observado em B. excelsa. O crescimento das mudas foi maior nas plantas expostas à luz solar em 180 minutos em ambas as espécies. Entretanto, as plantas de B. excelsa foram mais sensíveis ao estresse hídrico moderado. C. guianensis foi à especie que teve melhor desempenho fotossintético e crescimento sob estresse hídrico moderado e luz solar plena. Portanto, essa espécie tem grande potencialidade para ser testada em programas de reflorestamento

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

Mudanças fisiológicas associadas à pré-aclimatação em quatro espécies florestais da Amazônia

Information on ecophysiological and silvicultural aspects of most tree species used for reforestation, conservation or reclamation of degraded lands is still limited. Solar radiation is a major factor influencing the survival, growth and development of plants. However, the nature of the morphogenic response may vary considerably among species, according to their acclimatization capability, as well as physiological changes observed in forest species under water stress. The overall objective was to obtain information about how Bertholletia excelsa, Carapa guianensis, Swietenia macrophylla and Hymenaea courbaril respond to changes in the physical environment during the acclimatization process. Gas exchanges, specific leaf area (AFE), chlorophyll fluorescence (the Fv/Fm ratio), survival rate, the monthly increase in height and diameter, leaf nutrient content and dry matter production were assessed in six independent pre-acclimation treatments to full sunlight (TPS) (0, 90, 180, 360, 540 and 720 min) followed by a whole-day exposure to full sunlight during 120 days. Every full sun acclimation treatment (30+120 days) was assessed at two water regimes: seedlings kept at field capacity (hereinafter termed without water stress, SE) and seedlings subjected to mild water restriction (herein termed with moderate water stress, CE). The mean highest maximum photosynthesis (Amax) was found in C. guianensis and S. macrophylla under CE conditions. The maximum carboxylation velocity of Rubisco (Vcmax25) and the maximum electron transport rate (Jmax25) were higher under outdoor conditions than under shading, in all studied species. AFE values were similar in all TPS, as in TH in all species studied, however, in H. courbaril the highest values were found in seedlings under SE conditions. Fv/Fm values decreased after the plants were transferred to full sunlight, particularly in B. excelsa under CE and H. courbaril. The survival rate was maximum (100%) for C. guianensis than in the other species. For H. courbaril, a TPS of 720 min, under CE condition was inadequate since in these treatments the survival rate was 0%. The rates of monthly increase in height and diameter were higher in S. macrophylla than in other species. It was also observed that S. macrophylla had reduced growth when exposed to low light intensity (TPS = 0). The mean leaf nitrogen content across species was higher in the CE treatment than in the SE one. With regard to phosphorus, their values were similar over species for TPS. The same was true for potassium. Calcium and magnesium were higher in S. macrophylla and C. guianensis than in B. excelsa or H. courbaril. Total biomass gain was greater in S. macrophylla and C. guianensis than in the others. For species the largest biomass accumulation occurred in the stem under SE conditions (143.4 g plant-1) and leaf (27.2 g plant-1) respectively. In general, the results obtained in this study indicate that C. guianensis and S. macrophylla have potential to be tested in field experiments on a wide range of environmental conditions because of their high capability to endure stressful conditions caused by sudden exposure to full sunlight and water stress.Informações sobre os aspectos silviculturais e ecofisiológicos da maioria das espécies arbóreas para programas de reflorestamento, conservação ou recuperação de áreas degradadas são ainda limitadas. A radiação solar é um dos principais fatores que influenciam a sobrevivência, o crescimento e o desenvolvimento dos vegetais. Todavia, a natureza da resposta morfogênica pode variar, consideravelmente, entre espécies, de acordo com a capacidade de aclimatação, assim como as mudanças fisiológicas observadas em espécies florestais sob estresse hídrico. O objetivo geral foi obter informações de como as mudas de Bertholletia excelsa, Carapa guianensis, Swietenia macrophylla e Hymenaea courbaril respondem a alterações no ambiente físico durante o processo de aclimatação. As trocas gasosas, a área foliar específica (AFE), a fluorescência da clorofila a (relação Fv/Fm), a taxa de sobrevivência, o incremento mensal em altura e diâmetro, os teores de nutrientes foliares e a produção da matéria seca foram avaliados ao final do experimento (30+120 dias) em seis tratamentos independentes de pré-aclimatação a luz solar plena (TPS) (0, 90, 180, 360, 540 e 720 min) e dois tratamentos hídricos (TH): mudas mantidas na capacidade de campo, chamado de sem estresse hídrico (SE) e mudas submetidas à restrição hídrica, chamado de com estresse hídrico moderado (CE). A maior média da fotossíntese máxima (Amax) foi encontrada em C. guianensis e S. macrophylla em condições de CE. A velocidade máxima de carboxilação da Rubisco (Vcmax25) e a taxa máxima de transporte de elétrons (Jmax25) foram maiores no ambiente a pleno sol do que sob sombreamento em todas as espécies estudadas. Os valores da AFE foram similares nos TPS, assim como nos TH em todas as espécies estudadas, já, em H. courbaril foram encontrados os maiores valores nas mudas sem estresse hídrico. A diminuição nos valores de Fv/Fm após a transferência para a luz solar plena mostrou a ocorrência de danos aos centros de reação do fotossistema II, sendo mais evidente em B. excelsa e H. courbaril sob condições de CE. A maior taxa de sobrevivência encontrada foi de 100% em C. guianensis do que nas outras espécies. Para H. courbaril as mudas submetidas ao tempo de pré-aclimatação de 720 min com estresse hídrico moderado, mostrou-se inadequado uma vez que nesse tratamento a taxa de sobrevivência foi de 0%. As taxas de incremento mensal em altura e diâmetro foram maiores em S. macrophylla do que nas outras espécies. Observou-se também que S. macrophylla teve seu crescimento reduzido quando exposta a baixa intensidade de luz (TPS = 0). A média dos valores de nitrogênio foliar nas espécies foi maior no tratamento com estresse hídrico moderado do que no sem estresse hídrico. Para o fósforo e o potássio os valores foram similares entre as espécies nos tempos de pré-aclimatação. Os conteúdos de cálcio e o magnésio foram maiores em S. macrophylla e C. guianensis do que em B. excelsa e H. courbaril. O acúmulo de biomassa total foi maior em S. macrophylla e C. guianensis. Nessas espécies o maior acúmulo de biomassa ocorreu no caule no experimento sem estresse hídrico (143,4 g planta-1) e na folha (27,2 g planta-1) respectivamente. Em geral, os resultados obtidos nesta pesquisa, indicam que C. guianensis e S. macrophylla apresentam potencial para serem testadas em experimentos de campo numa faixa mais ampla de condições ambientais e por apresentarem maior tolerância ao estresse hídrico

Ecofisiologia em mudas de acariquara (minquartia guianensis aubl.) e mogno (swietenia macrophylla king.) aclimatadas à campos abertos

The objective of this research was to study the ecophysiological behavior of saplings of acariquara (Minquartia guianensis Aubl.) and mahogany (Swietenia macrophylla King.) during acclimation to full sunlight. The experiment was conducted at the Campus V-8 of the National Institute for Research in the Amazon (INPA) in Manaus, between June and December of 2008. The acclimation periods (TS) were: 0 (T0, control, kept under shade, at 0.40 mol m-2 day-1), 30 (T30), 60 (T60), 90 (T90), 120 (T120), 150 (T150) and 180 days (T180). At each acclimation treatment, five saplings (replicates) per species were used. At the end of acclimation treatments were measured: the Fv/Fm ratio, photosynthetic rates (A), stomatal conductance (gs), maximum carboxilation rate of Rubisco (Vcmax), maximum rate of electron transport (Jmax), transpiration (E), leaf water potential (Ψf), height, diameter, number of leaves, specific leaf area (AFE), and chlorophyll and carotenoid contents. Gas exchange rates were measured with a photosynthesis meter (Li-6400, Li-Cor, USA). In acariquara, transfer to full sunlight immediately caused severe photoinhibition, which in some cases evolved to leaf photooxidation and premature leaf abscission. In this species, little production of new leaves during the experiment was observed. On the contrary, mahogany showed abundant production of leaves (and little leaf abscission) and absence of leaf photooxidation. The sudden plant exposure to full sunlight caused severe reduction in the Fv/Fm ratio, which was more pronounced in acariquara. However, at the end of the acclimation period, saplings of both species showed almost full recovery again photoinhibition, with Fv/Fm values close to those observed in control plants. Thus, in the last three months of the acclimation period to full sunlight, Vcmax was 12.9 μmol m-2 s-1 for acariquara and 20.4 μmol m-2 s-1 for mahogany, while the potential photosynthesis (Apot) for the same period, was 8.2 μmol m-2 s-1 for acariquara and 10.2 μmol m-2 s-1 for mahogany. There was no effect of the acclimation process on Ψf. Finally, the higher photosynthetic rate observed in mahogany also coincided with higher growth rates in this species, which grew about three times faster (growth in diameter of 0.9 mm month-1) than acariquara (0.25 mm month-1).O objetivo desta pesquisa foi estudar a resposta ecofisiológica de mudas de acariquara (Minquartia guianensis Aubl.) e mogno (Swietenia macrophylla King.) aclimatadas à radiação solar plena. O experimento foi realizado no campus V-8 do Instituto Nacional de Pesquisas da Amazônia (INPA) em Manaus, entre junho e dezembro de 2008. Utilizaram-se os seguintes tempos de solarização (TS): 0 (T0, controle, mantido na sombra a 0,40 mol m-2 dia-1), 30 (T30), 60 (T60), 90 (T90), 120 (T120), 150 (T150) e 180 dias (T180). Em cada TS foram usadas cinco mudas (repetições) por espécie. Ao final do período de aclimatação foram mensuradas: a relação Fv/Fm, as taxas de fotossíntese (A), a condutância estomática (gs), a velocidade máxima de carboxilação da Rubisco (Vcmax), a taxa máxima de transporte de elétrons (Jmax), a transpiração (E), o potencial hídrico da folha (Ψf), a altura, o diâmetro, o número de folhas, a área foliar especifica (AFE) e o teor clorofilas e carotenóides. Os dados de trocas gasosas foram mensuradas com um medidor de fotossíntese (Li-6400, Li-Cor, EUA). Na acariquara, a transferência à luz solar plena causou, no inicio do experimento, fotoinibição severa que em alguns casos evoluiu para fotooxidação foliar e abscisão prematura de folhas; observando-se nesta espécie pouca produção de novas folhas, ao longo do experimento. Ao contrário, no mogno houve produção abundante de folhas (e pouca abscisão) e ausência de fotooxidação foliar. A exposição súbita das plantas à alta radiação solar causou diminuição severa na relação Fv/Fm, sendo mais acentuada na acariquara. No entanto, ao final do período de aclimatação, tanto as mudas de acariquara como as de mogno apresentaram recuperação da fotoinibição, atingindo a relação Fv/Fm valores próximos aos observados no controle. Assim, nos últimos três meses do período de aclimatação à luz solar plena, Vcmax foi de 12,9 μmol m-2 s-1 para acariquara, e de 20,4 μmol m-2 s-1 para o mogno; já a fotossíntese potencial (Apot), para o mesmo período, foi de 8,2 μmol m-2 s-1 para acariquara e 10,2 μmol m-2 s-1 para o mogno. Não houve efeito do processo de aclimatação no potencial hídrico da folha (Ψf). Finalmente, a maior taxa de fotossíntese observada no mogno coincidiu com as maiores taxas de crescimento nesta espécie, sendo estas aproximadamente três vezes maiores no mogno (crescimento em diâmetro de 0,9 mm mês-1) do que na acariquara (0,25 mm mês-1)