Photosynthetic response of poikilochlorophyllous desiccation-tolerant Pleurostima purpurea (Velloziaceae) to dehydration and rehydration

The poikilochorophyllous, desiccation-tolerant (PDT) angiosperm, Pleurostima purpurea, normally occurs in less exposed \ud rock faces and slightly shady sites. Our aim was to evaluate the light susceptibility of the photosynthetic apparatus during \ud dehydration-rehydration cycle in P. purpurea. In a controlled environment, the potted plants were subjected to water \ud deficit under two different photosynthetic photon flux densities [PPFD, 100 and 400 µmol(photon) m–2 s–1]. In the higher \ud PPFD, net photosynthetic rate (PN) become undetectable after stomata closure but photochemical efficiency of \ud photosystem II, electron transport rate, and photochemical quenching coefficient were maintained relatively high, despite \ud a partial decrease. The photochemical activity was inhibited only after the complete loss of chlorophylls, when leaf relative \ud water content dropped below 72% and total carotenoids reached maximal accumulation. Nonphotochemical energy \ud dissipation increased earlier in response to dehydration under higher PPFD. PN and photochemical activity were fully \ud recovered after rehydration under both light treatments. Our results suggested that the natural occurrence of P. purpurea \ud should not be restricted by the light intensity during the complete desiccation-rehydration cycles.Fundação de Amparo à Pesquisa do Estado de São PauloCoordenação de Aperfeiçoamento de Pessoal de Nível Superior (CAPES

Photosynthetic response of poikilochlorophyllous desiccation-tolerant Pleurostima purpurea (Velloziaceae) to dehydration and rehydration.

The poikilochorophyllous, desiccation-tolerant (PDT) angiosperm, Pleurostima purpurea, normally occurs in less exposed rock faces and slightly shady sites. Our aim was to evaluate the light susceptibility of the photosynthetic apparatus during dehydration-rehydration cycle in P. purpurea. In a controlled environment, the potted plants were subjected to water deficit under two different photosynthetic photon flux densities [PPFD, 100 and 400 μmol(photon) m?2 s?1]. In the higher PPFD, net photosynthetic rate (PN) become undetectable after stomata closure but photochemical efficiency of photosystem II, electron transport rate, and photochemical quenching coefficient were maintained relatively high, despite a partial decrease. The photochemical activity was inhibited only after the complete loss of chlorophylls, when leaf relative water content dropped below 72% and total carotenoids reached maximal accumulation. Nonphotochemical energy dissipation increased earlier in response to dehydration under higher PPFD. PN and photochemical activity were fully recovered after rehydration under both light treatments. Our results suggested that the natural occurrence of P. purpurea should not be restricted by the light intensity during the complete desiccation-rehydration cycles. Additional key words: chlorophyll fluorescence; gas exchange; photoprotective mechanisms; vegetative desiccation toleranc

Análise conjunta de atributos físicos e biológicos do solo sob sistema de integração lavoura-pecuária

O objetivo deste trabalho foi avaliar os efeitos do sistema integração lavoura-pecuária (ILP) sobre os atributos morfológicos, físicos e biológicos do solo. O experimento foi realizado em Dourados, MS, em Latossolo Vermelho distroférrico típico. Foram avaliados os seguintes sistemas: monocultura com sistema convencional de preparo do solo, ILP com sistema plantio direto, pastagem contínua de Urochloa decumbens (Syn. Brachiaria decumbens) e vegetação nativa. Em cada sistema, foi aberta uma trincheira com o intuito de detectar as modificações morfológicas provocadas pelos diferentes manejos com uso do método do perfil cultural. Os macroinvertebrados do solo foram avaliados conforme o método "Tropical Soil Biology and Fertility". Utilizaram-se, ainda, amostras de solo indeformadas para avaliação dos atributos físicos do solo (densidade do solo, porosidade total, macro e microporosidade). Entre os sistemas produtivos, a melhor estrutura do solo foi verificada no sistema ILP, nas camadas de 0-0,1 e 0,1-0,2 m. Os sistemas sob ILP e em pastagem cultivada continuamente favoreceram um ambiente edáfico biologicamente mais ativo em comparação aos outros sistemas cultivados. A visualização conjunta dos atributos do solo mostrou que a integração lavoura-pecuária é uma estratégia para desenvolver sistemas de produção sustentáveis e que o período de dois anos de manejo é adequado para a rotação lavoura-pecuária