Avaliação sazonal da atividade da fenilalanina amonia-liase e dos teores de fenois e taninos totais em Byrsonima verbascifolia Rich. ex. A. Juss.: uma especie medicinal do cerrado.

An experiment was conducted, ever month, from november, 2001 to september, 2002 in order to investigate the influence of seasonal variation of physical environment on gas exchange, on leaf water state, on the phenylalanine ammonia-lyase activity and on the total phenolic and tannin contents of murici,. The used area was a praire with a physionomy of Cerrado stricto sensu, located in Ijaci, south of the State of Minas Gerais. For the evaluation, plants Were selected with an average height of 2.70 +/- 0.21 m and an average basal diameter of 0.15 +/- 0.04 m. Leaf potential at 7 and 12 am and gas exchange at 10 and 12 am was evaluated ever month. The results showed that the leaf water potential was not significant seasonal variations indicating that the plants were in similar water conditions in both dry and rainy seasons. Higher photosynthetic and transpiration rates-were observed during rainy season. The net photosynthesis showed higher in the morning, although no significant variations of transpiration on the evaluating hours were observed. The stomatal conductance reached similar Values in both seasons, suggesting a participation of non-stomatal factors on the seasonal variation observed for the-gas exchange. It. was also observed significant seasonal variations on enzyme activity and total tannins contents. The increase of the phenylalanine ammonia-lyase activity and decrease Of the total tannins contents were characteristic of the dry season. The levels of total phenolics. had not varied significantly during the dry and rainy seasons, while the total tannin contents followed the photosynthetic response of plants, the enzyme activity was much more influenced by environmental conditions

Decomposition of Arachis pintoi and Hyparrhenia rufa litters in monoculture and intercropped systems under lowland soil.

ABSTRACT - Tropical grasslands under lowland soils are generally underutilized and the litter of forage legumes may be used to recover these degraded pastures. The objective of this work was to study the dynamics of litter decomposition of Arachis pintoi (pinto peanut), Hyparrhenia rufa (thatching grass) and a mixture of both species in a lowland soil. These treatments were analyzed in three areas: grass monoculture, legume monoculture and legume intercropped with the grass during the dry and wet seasons. Litter bags containing the legume, grass or a mixture of both species were incubated to estimate the decomposition rate and microorganism colonization. Decomposition constants (K) and litter half-lives (T1/2) were estimated by an exponential model whereas number of microorganisms in specific media were determined by plate dilution. The decomposition rate, release of nutrients and microorganisms number, especially bacteria, increased when pinto peanut was added to thatching grass, influenced by favorable lignin/N and C/N ratios in legume litter. When pinto peanut litter was incubated in the grass plots, 50% N and P was released within about 135 days in the dry season and in the wet season, the equivalent release occurred within 20 days. These results indicate that A. pintoi has a great potential for nutrient recycling via litter and can be used to recover degraded areas. RESUMO - Pastagens tropicais sobre solos de várzea são geralmente subutilizadas. A serrapilheira de leguminosas forrageiras pode ser usada para a recuperação destas pastagens. O objetivo deste trabalho foi estudar a dinâmica de decomposição de Arachis pintoi (arachis), Hyparrhenia rufa (capim jaraguá) e da mistura destas espécies, em solo de várzea. Estes tratamentos foram analisados em três áreas: monocultivo da gramínea; monocultivo da leguminosa e no consórcio entre as espécies durante as estações seca e chuvosa. Sacos de decomposição contendo a serrapilheira da leguminosa ou da mistura das espécies foram incubados para estimar a taxa de decomposição e colonização microbiana. A taxa de decomposição e o tempo de meia-vida (T1/2) foram estimados por um modelo exponencial, e o número de microrganismos foi determinado por meio de diluição em placas em meios específicos. A liberação de nutrientes, a taxa de decomposição, e o número de microrganismos, especialmente bactérias, aumentaram quando arachis foi adicionado ao capim jaraguá, com influência da relação favorável de lignina/N e C/N do resto desta cultura. Quando arachis foi incubado em parcelas de monocultivo da gramínea, 50% do total de N e P foi liberado em 135 dias na estação seca e em 20 dias na estação chuvosa. Estes resultados indicam que A. pintoi tem um grande potencial para ciclagem de nutrientes e pode ser uma estratégia na recuperação de áreas degradadas