Patrícia Carneiro Souto

Comunidade microbiana e mesofauna edáficas em solo sob caatinga no semi-árido da Paraíba

The biological soil activity is responsible for several physical and chemical transformations of deposited organic residues, therefore maintaining the environmental sustainability. The aim of this study was to evaluate the distribution of the soil microbial community and mesofauna in a dry forest (Caatinga) in the semi-arid region of Paraiba, northeastern Brazil. To determine the microorganism population soil samples from the 0-15xa0cm soil layer were evaluated. Total counts of fungi and bacteria were evaluated in specific culture media. The Berleusse-Tullgren modified method was used to extract the soil mesofauna. Oscillations in the soil water content and high temperatures promoted variations in the microbial population. The fungi population was larger than that of bacteria in both years of the study period, probably due to the slightly acidic soil pH. Shannons index (H) and Pielous index (e) also varied according to the season of the year. The most important mesofauna groups are Diptera (42.5xa0%), Acarinae (40.3xa0%) and Collembola (8.8xa0%). These groups play an important role in nutrient cycling in dry forest sites.

Crescimento e nutrição mineral do nim ( Azadirachta indica A. Juss.) e cinamomo ( Melia azedarach Linn.) submetidos à salinidade.

The objective of this study was to verify the effects of soil salinity on growth and nutrient and sodium accumulation in neem ( Azadirachta indica ) and cinnamomum ( Melia azedarach ). The experimental delineation was completely randomized in a 2 x 4 factorial arrangement, with two species (neem and cinnamomum), four salinity levels (electrical conductivity 0.49 (non saline soil), 4.15, 6.33 and 10.45 dS m -1 ) and four replications. Initially, plants were grown in tubes, and 60 days after emergence, they were transferred to pots containing 3 kg of substrate [soil + manure (2:1)], according to the saline treatment. After 45 days, plant height, dry matter (leaves, stem, shoot (stem + leaves), roots and total) and N, P, K, Ca, Mg, S and Na + shoot accumulation were evaluated. Salinity reduced the plant height in both species, but the effect was more pronounced in neem. Increases in soil salinity caused an increase in the accumulation of Na + and reduced the accumulation of nutrients in shoots of both species, especially in neem. The cinnamomum was more tolerant to salinity levels of soils than neem.

Carbon and nutrient fluxes through litterfall at four succession stages of caatinga dry forest in northeastern Brazil.

Knowledge about litterfall and its nutrient fluxes is important for understanding ecosystem dynamics, especially in regards to vegetation at different succession stages. Regenerating vegetation represents a large proportion of tropical forests, such as the caatinga dry forest in NE Brazil, which is heavily used for fuel wood and slash-and-burn agriculture. In the present study we measured litterfall for 2xa0years in four regeneration stages of caatinga: recently abandoned pasture, 15-, 37-, and 57-years (mature caatinga) of regeneration. The lowest litter C fluxes were observed in pasture sites but the highest fluxes occurred in the intermediate regeneration stages (15 and 37xa0years of regeneration) than in the mature caatinga. The 15-year site had the highest concentrations and the greatest fluxes of nitrogen and phosphorus. Nutrient concentrations in litter were in the range of those found in other dry forests, but the fluxes were lower. The high N:P concentration ratios indicate that P is a limiting nutrient in this ecosystem. The proportion of total litterfall C fluxes relative to total C stocks in the ecosystem decreased consistently with succession age, but annual net C accumulation in the ecosystem increased with succession age. The results suggest that litterfall in earlier regeneration stages is more strongly affected by rainfall variation than mature vegetation, but these patterns need to be further investigated for longer periods. This higher stability of mature ecosystems could be important in face of the expected higher climatic variability in the future.

Taxa de decomposição da serapilheira e atividade microbiana em área de Caatinga

Objetivando avaliar a decomposicao da serapilheira e a atividade microbiana em area de Caatinga preservada, conduziu-se um experimento na Reserva Particular do Patrimonio Natural Fazenda Tamandua, em Santa Terezinha, Estado da Paraiba. A taxa de decomposicao foi determinada com o uso de sacolas de nailon, contendo 30 g de serapilheira, que foram dispostas na superficie do solo em setembro de 2003, sendo retiradas 20 sacolas mensalmente ate setembro de 2005. O material coletado foi seco em estufa e pesado para avaliar a perda de peso em relacao ao peso inicial. A atividade microbiana foi estimada mensalmente pela quantificacao do dioxido de carbono (CO2) liberado no processo de respiracao edafica, a partir da superficie do solo, e capturado por solucao de KOH. A perda de peso da serapilheira, apos um ano, foi de 41,19% e, apos dois anos, foi de 48,37%, evidenciando uma decomposicao mais acelerada no primeiro ano. A analise dos dados mostrou a influencia da estacao do ano na decomposicao de serapilheira e da temperatura na atividade microbiana.

DIVERSIDADE DO BANCO DE SEMENTES EM DIFERENTES ÁREAS DE CAATINGA MANEJADAS NO SEMIÁRIDO DA PARAÍBA, BRASIL

Caatinga, the predominant vegetation type of the semiarid region of northeastern Brazil, is composed by plants showing efficient mechanisms to keep them in the ecosystem. The herbaceous, bush and tree strata provide food for animals and several products for human use, and supply seedbank with propagules to assure plant recovery. The objective of this study was to compare seedbank density, composition and diversity of three sites with different vegetation physiognomies: craibeira plantation site (A1), degraded site (A2) and juremas + sabia plantation site (A3), located at the Nupearido Experimental Station/Federal University of Campina Grande (UFCG), Patos, PB state, Brazil. Five litterfal + soil samples were collected in each site and taken to the Forestxa0 Nursery of UFCG Campus in Patos and kept under a 50% solar radiation reduction plastic screen and a daily manual irrigation regimen, where they were observed during 90 days for counting and identification of the emerging seedlings. Plantule density for each site was compared by the χ 2 test (P<0.05). Plant diversity and species richness were evaluated by Shannon-Wiener (H’) and Pielou Uniformity (e”) indexes, respectively. Herb species predominated in seedbank of all sites, and the number of seeds of tree species increased in the craibeira plantation site resulting from the prolonged presence of animals attracted by the thermal comfort under tree canopy.