forest ecosystems sequester large amounts of atmospheric co 2 , and the contribution from seasonally dry tropical forests is not negligible. thus, the objective of this study was to quantify and evaluate the seasonal and annual patterns of co 2 exchanges in the Caatinga biome, as well as to evaluate the ecosystem condition as carbon sink or source during years. in addition, we analyzed the climatic factors that control the seasonal variability of gross primary production (Gpp), ecosystem respiration (R eco) and net ecosystem co 2 exchange (nee). Results showed that the dynamics of the components of the co 2 fluxes varied depending on the magnitude and distribution of rainfall and, as a consequence, on the variability of the vegetation state. Annual cumulative NEE was significantly higher (p < 0.01) in 2014 (−169.0 g C m −2) when compared to 2015 (−145.0 g C m −2) and annual NEP/GPP ratio was 0.41 in 2014 and 0.43 in 2015. Global radiation, air and soil temperature were the main factors associated with the diurnal variability of carbon fluxes. Even during the dry season, the NEE was at equilibrium and the Caatinga acted as an atmospheric carbon sink during the years 2014 and 2015. CO 2 concentration has a high interannual variability due to its absorption by terrestrial ecosystems (carbon sinks) 1-5. However, despite this variability, data show a systematic increase in CO 2 throughout the years 6,7. In South America, the Amazon forest is an example of a terrestrial carbon sink (considering its 20-year mean behavior), although it has occasionally behaved as CO 2-neutral or even a carbon source in the last years 8. Interannual variability and trends in CO 2 sinks are controlled by different biogeographic regions. The annual mean behavior of sinks is controlled mainly by highly productive lands, such as wet tropical forests (i.e. the Amazon forest) 5. On the other hand, semiarid environments control the global scale trends observed in the last few decades 9,10. Despite its prominent role, there is still much to be studied and investigated regarding CO 2 exchanges in these regions, which are still much less understood than wet forests or croplands 5,10. According to the literature 10 , gaps in understanding CO 2 exchanges in these environments have limited our ability to understand and predict interannual and decadal variations on global scale carbon cycle. There are a few inherent difficulties when quantifying CO 2 exchanges in semiarid environments, such as the rapid expansion of some of its areas due to climate change and anthropic activities 11,12. Studies show that some regions in South America are becoming more arid, such as the Amazon 13,14 ; the Brazilian semiarid region, dominated by the Caatinga biome, which is a seasonally dry tropical forest (SDTF) 15-17 and the Cerrado, which is a Brazilian savanna-type vegetation 18 .
An understanding of variations in morphophysiological leaf traits of plant models in dry tropical forests is essential for quantifying C fluxes from forest ecosystems in response to climate changes. The present study evaluated the influences of seasonal rainfall and different light conditions on the gas exchange, nutrients, organic compounds and morphological traits in Croton blanchetianus Baill. trees within a fragment of Caatinga forest. Stomatal conductance (gs) and net photosynthesis (PN) demonstrated variations within the diurnal cycle, with maximum values at approximately midday and minimum values at predawn. The PN and the diurnal integrated CO2 assimilation were lower during the dry season than in the rainy season. Water use efficiency was positively correlated with PN (r = 0.73) during the dry season only. However, the correlation between PN and gs was observed during the rainy season only (r = 0.60). Thus we demonstrated that C. blanchetianus has a remarkable ability to adapt to global climatic changes and could be considered a model in studies exploring water relationships in woody plants; consequently, this species may be important in future reforestation studies.
Global climate models predict changes on the length of the dry season in the Amazon which may affect tree physiology. The aims of this work were to determine the effect of the rainfall regime and fraction of sky visible (FSV) at the forest understory on leaf traits and gas exchange of ten rainforest tree species in the Central Amazon, Brazil. We also examined the relationship between specific leaf area (SLA), leaf thickness (LT), and leaf nitrogen content on photosynthetic parameters.
-The seed technologies related with germination and seed research has provided unprecedented opportunities for the biologic research community. Researchers require such information to rapidly determine the speed of seedling emergence. However, an immense amount of data must be analyzed to achieve this goal. In this paper, we introduce a computer software designed for broad use to facilitate the understanding of germination processes and their analysis. GerminaQuant 1.0 was written in the C++ programming language and presents a user-friendly interface. The accuracy of the software was tested using fifty different matrices, whose output values were compared with other spreadsheets available on the web. With data analysis, we showed that the GerminaQuant is capable of generating mathematical calculations with extreme accuracy, besides have a good performance and wide ease of use in any kind of computer. In addition, the new software has been tested by at least eighty users, which compared functionality, designer and accuracy of the output data. In all variables, the GerminaQuant was evaluated as superior compared to other spreadsheets available on the web. ) is freely available to the scientific community and can be easily downloaded from the website (http://www.ufpe.br/lev).Index terms: mean germination time, seed germination, software, spreadsheet, synchrony and uncertainty of germination.GerminaQuant: uma nova ferramenta para cálculos de germinação RESUMO -A avaliação da velocidade e intensidade de germinação de lotes de sementes têm providenciado oportunidades sem precedentes para a comunidade científica. Pesquisadores requerem tais informações para rapidamente determinar a velocidade de emergência da plântula. Entretanto, uma quantidade extensa de dados é analisada para se alcançar este propósito. Neste artigo, introduzimos um software desenhado para facilitar o entendimento dos processos de germinação e a análise dos dados. O GerminaQuant 1.0 foi escrito em linguagem de programação C++ e apresenta uma interface amigável. A precisão do software foi testada a partir de cinquenta diferentes matrizes, cujos valores de saída foram comparados com outras planilhas de cálculo disponíveis na web. Com a análise dos dados foi mostrado que o GerminaQuant é capaz de gerar cálculos matemáticos com extrema precisão, além de apresentar uma performance amigável, com ampla facilidade de uso em qualquer computador. Ademais, o novo software foi testado para oitenta usuários, os quais compararam a sua funcionalidade design e precisão. Em todas as variáveis, o GerminaQuant foi avaliado como sendo superior quando comparado às demais planilhas disponíveis na web. O GerminaQuant (disponível para Windows ® , Macintosh ® e Linux ® ) está disponível gratuitamente para download por toda a comunidade científica, através do endereço http://www.ufpe.br/lev. Temos para indexação: tempo médio de germinação, germinação de sementes, software, planilhas eletrônicas, sincronia e incerteza na germinação.
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