Efeitos das variações de temperatura relacionados às mudanças climáticas globais sobre as respostas fotossintéticas de macroalgas lóticas tropicais
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Data
2016-07-26
Autores
Vilas Boas, Lucas Kortz [UNESP]
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Universidade Estadual Paulista (Unesp)
Resumo
Apesar da existência de ciclos de alterações da temperatura média global na história da Terra, atividades antrópicas têm causado um aumento das concentrações de gases do efeito estufa na atmosfera desde a revolução industrial, causando mudanças climáticas já observadas nas últimas décadas. Tais mudanças climáticas afetam os organismos de ambientes aquáticos continentais, incluindo os produtores primários (p.ex., macroalgas). Utilizando as técnicas da evolução da concentração de oxigênio dissolvido, da concentração de pigmentos fotossintetizantes e da fluorescência da clorofila a, avaliou-se o efeito do aumento de temperatura devido ao aquecimento global, previsto em dois cenários futuros (RCP 4.5 e RCP 8.5 do Painel Intergovernamental de Mudanças Climáticas - IPCC) sobre as respostas fotossintéticas de macroalgas lóticas. As temperaturas controle foram determinadas, para os períodos de inverno e verão, a partir da temperatura média de riachos da região onde as amostras de macroalgas (Filos Rhodophyta, Cyanobacteria e Chlorophyta) foram coletadas e as temperaturas experimentais calculadas adicionando-se os aumentos previstos pelos cenários testados do IPCC. A resposta à simulação dos cenários do IPCC se deu de modo espécie-específico, contudo, os resultados gerais indicaram que dentre as espécies testadas, as Rhodophyta (Batrachospermum helminthosum Bory, Sirodotia delicatula Skuja e estágio “Chantransia”) teriam sua eficiência fotossintética prejudicada com o aumento de temperatura, principalmente no cenário RCP 8.5 no verão. Adicionalmente, a maior parte das Chlorophyta investigadas não mostrou perdas significativas na produtividade, com algumas espécies demonstrando inclusive uma melhor performance nos cenários experimentais em relação ao controle. Dessa maneira, na possível concretização do cenário RCP 8.5, a contribuição autóctone das Rhodophyta em riachos seria prejudicada, um efeito que poderia impactar em toda a teia trófica, especialmente em ambientes lóticos sombreados de baixas ordens, onde algas vermelhas estão entre os principais produtores primários. Ao mesmo tempo, a eventual confirmação das previsões do cenário RCP 8.5 poderia produzir um aumento na riqueza, abundância e distribuição de algas verdes, podendo impactar em aspectos importantes das comunidades de produtores primários dos ambientes lóticos.
Despite the existence of global mean temperature shift cycles in Earth’s history, anthropogenic activities have been causing an increase in the concentration of greenhouse gases since the industrial revolution, inducing the climate changes already observed over the last decades. Such climate changes affect freshwater organisms, including primary producers (i.e. macroalgae). Using the techniques of dissolved oxygen evolution, photosynthetic pigments concentration and chlorophyll a fluorescence, we evaluated the effect of projected temperature increase due to global warming of two future scenarios (RCP 4.5 and RCP 8.5 of the Intergovernmental Panel on Climate Change – IPCC) on the photosynthetic response of lotic macroalgae. Control temperatures were determined, for summer and winter seasons, from the mean temperature of streams of the region where macroalgae samples (phyla Rhodophyta, Cyanobacteria and Chlorophyta) were collected and experimental temperatures were calculated adding the projected increase of the tested IPCC scenarios. The response to the IPCC scenarios simulation showed a species-specific pattern, although results in general indicated that within tested species, the red algae (Batrachospermum helminthosum Bory, Sirodotia delicatula Skuja and “Chantransia” stage) would have their photosynthetic efficiency impaired with temperature increase, especially in scenario RCP 8.5 during the summer. In addition, most Chlorophyta investigated did not show a significant productivity loss, with some species demonstrating an improved performance in the experimental scenarios. Hence, if global warming scenario RCP 8.5 comes to occur, the autochthonous contribution of Rhodophyta would be jeopardized, an effect that could propagate throughout the entire food web, especially in shaded, low-order, lotic ecosystems, where red algae are among the main primary producers. Furthermore, the eventual confirmation of RCP 8.5 scenario predictions could result in a boost of green algae richness, abundance and distribution, which may impact important aspects of the primary producers’ community in lotic environments.
Despite the existence of global mean temperature shift cycles in Earth’s history, anthropogenic activities have been causing an increase in the concentration of greenhouse gases since the industrial revolution, inducing the climate changes already observed over the last decades. Such climate changes affect freshwater organisms, including primary producers (i.e. macroalgae). Using the techniques of dissolved oxygen evolution, photosynthetic pigments concentration and chlorophyll a fluorescence, we evaluated the effect of projected temperature increase due to global warming of two future scenarios (RCP 4.5 and RCP 8.5 of the Intergovernmental Panel on Climate Change – IPCC) on the photosynthetic response of lotic macroalgae. Control temperatures were determined, for summer and winter seasons, from the mean temperature of streams of the region where macroalgae samples (phyla Rhodophyta, Cyanobacteria and Chlorophyta) were collected and experimental temperatures were calculated adding the projected increase of the tested IPCC scenarios. The response to the IPCC scenarios simulation showed a species-specific pattern, although results in general indicated that within tested species, the red algae (Batrachospermum helminthosum Bory, Sirodotia delicatula Skuja and “Chantransia” stage) would have their photosynthetic efficiency impaired with temperature increase, especially in scenario RCP 8.5 during the summer. In addition, most Chlorophyta investigated did not show a significant productivity loss, with some species demonstrating an improved performance in the experimental scenarios. Hence, if global warming scenario RCP 8.5 comes to occur, the autochthonous contribution of Rhodophyta would be jeopardized, an effect that could propagate throughout the entire food web, especially in shaded, low-order, lotic ecosystems, where red algae are among the main primary producers. Furthermore, the eventual confirmation of RCP 8.5 scenario predictions could result in a boost of green algae richness, abundance and distribution, which may impact important aspects of the primary producers’ community in lotic environments.
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Palavras-chave
Mudanças climáticas, Temperatura, Fotossíntese, Macroalgas, Climate change, Temperature, Photosynthesis