Canopy cover has significant effects on the understory environment, including upon light availability for seedling growth. The aim of the present study was to verify spatial heterogeneity and seasonal changes in the canopy cover of a dense Cerrado area, and their relationship to understory photosynthetic active radiation availability. Leaf area index (LAI) values in the rainy season varied from 0.9 to 4.83, with 40% of the values ranging from 4.0 to 5.0, while in the dry season LAI varied from 0.74 to 3.3, with 53% of the values oscilating from 2.0 to 3.0. Understory light (Q i ) and the Lambert-Beer ratio (Q i /Q o ) were taken around noon on sunny days (between 11:00 AM and 1:00 PM). They were also statistically different (p < 0.01) between the dry and wet seasons, with 72% of sampled points in the rainy season presenting photosynthetic photon flux density (PPFD) values lower than 250 μmol.m -2 /s around noon, whereas in the dry season, most PPFD values varied from 1500 to 1817 μmol.m -2 /s , thus providing high light availability for understory plants. In most of the studied sites, understory plants did not even receive enough light for 50% of their photosynthetic capacity in the wet season. In contrast during the dry season, Q i /Q o values of 0.8 to 1.0 were observed in more than 50% of the points, thereby allowing for photosynthetic light saturation. Thus, light variability around noon was higher during the dry season than in the wet season, its heterogeneity being related to spatial complexity in the canopy cover.Keywords: leaf area index, Lambert-Beer ratio, photosynthesis, seedling growth, tropical savanna.Variabilidade espacial e temporal da cobertura do dossel e da luz no sub-bosque em uma área de Cerrado no Sudeste do Brasil ResumoA cobertura do dossel tem efeitos significativos no ambiente do sub-bosque incluindo a disponibilidade de luz para o crescimento das plântulas. O objetivo do presente estudo foi verificar a heterogeneidade espacial e as mudanças sazonais da cobertura do dossel em uma area de Cerrado denso e sua relação com a radiação fotossintetica ativa diponivel no sub-bosque. Os valores do índice de área foliar (IAF) na estação chuvosa variaram de 0,9 a 4,83 com 40% dos valores dentro de 4,0 a 5,0, enquanto na estação seca o IAF variou de 0,74 a 3,3 com 53% dos valores dentro de 2,0 a 3,0. A luz abaixo do dossel (Qi) e razão de Lambert-Beer (Qi/Qo) foi obtida entre as 11:00 e 13:00 horas em dias ensolarados. Os valores também foram estatisticamente diferentes (p < 0.01) entre a estação seca e a chuvosa, com 72% dos pontos amostrados na estação chuvosa apresentando valores de densidade de fluxo de fotons fotossinteticamente ativos (DFFA) menores de 250 μmol.m -2 /s por volta do meio dia, enquanto na estação seca a maioria dos valores de DFFA variou entre 1500 a 1817 μmol.m -2 /s propiciando alta disponibilidade de luz para o sub-bosque. Na maior parte dos pontos amostrados, as plantas de sub-bosque não receberam quantidade de luz suficiente para 50% de sua capacidade fotossintetic...

It is essential to know the ecological tolerance of Anadenanthera peregrina (L.) Speg seedlings regarding the light and edaphic conditions. The aim of this study was to evaluate the effect of substrates and shading levels on the emergence and quality of A. peregrina seedlings. The seeding was done in two substrates: 100% Dystroferric Red Latosol (DRL) and DRL + commercial substrate (1:1, v/v). The species were kept under four shading levels: 0% (direct sunlight), 30%, 50% and 70%. The highest speed and shortest emergence time of A. peregrina occurred in DRL. The highest growth characteristics of aerial part, xylopodium and roots occurred under direct sunlight and DRL. The productions of fresh and dried masses of different vegetative organs, physiological and Dickson quality index were higher in DRL and direct sunlight. The A. peregrina seedlings in 100% of DRL and direct sunlight showed more viable morphophysiological and quality indicators for their production.

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