Estrutura fitossociológica, produção de serapilheira e ciclagem de nutrientes em uma área de Caatinga no Seridó do Rio Grande do Norte

• Autor(a) principal: Santana, José Augusto da Silva
• Data de Publicação: 2005
• Tipo de documento: Tese
• Idioma: por
• Título da fonte: Biblioteca Digital de Teses e Dissertações da UFPB
• Texto Completo: https://repositorio.ufpb.br/jspui/handle/tede/8190
• topic: Caatinga; ciclagem de nutrientes; Matéria orgânica; CIENCIAS AGRARIAS::AGRONOMIA

The caatinga, larger bioma of the Brazilian Northeast, is still not very well-known and protected, with great part of its area being already degraded and presenting serious desertificação risks. In spite of the significant importance that carries in the regional economy, public politics don't exist for its recovery and maintainable use, staying the extrativism as the only exploration form. The aims of this work was to floristic characterize and to accomplish phytossociologic analysis of the shrub-tree component of the bioma; to quantify the litter production and of the three species with larger value of importance (IV); to characterize the pattern of the deposition dynamics of nutrients through litter of the vegetation and to evaluate of the decomposition process, nutrients liberation of the senescents leaves and litter accumulation. The work was developed in thirty plots of 20 m x 10 m in the caatinga of the Seridó Ecological Station, Serra Negra do Norte-RN. In the floristic study all individuals with 3 cm diameter at the level of the soil surface and larger height to 1 m were inventoried. For the phytossociologic analysis it was calculated the density, frequency and relative dominance, basal area and importance value (IV) for species and family, besides the floristic diversity floristic and richness taxionomic index. The quantification of the litter production was accomplished through twelve monthly collections in 30 collectors of 1 m2, embracing a rainy and dry period, with the material being dry for 48 hours, separated in the leaves of the bioma, leaves of the three species with greater IV, bark and branches, reproductive organs, miscellany and litter of the caatinga, and weighed. Were established correlations among the production for fraction and some varied climatic. The liberation of the macronutrientes (N, P, K, Ca, Mg and S) contained in the litter was determined by fractions and a month, being calculated in Mg.ha-1.ano-1. Was calculated the nutreint use efficiency by the leaves of the bioma and of the species with greater VI. The decomposição study was developed for twelve months, using 10 g of biomass to leaves drought in litterbags, contents a mixture of leaves of all the species of the bioma in the first treatment and leaves of the three species with larger VI in the other three treatments, with five repetitions. Were calculated the monthly medium loss of biomassa, the macronutrientes liberation, the time to degraded 50 % of the initial biomassa, the serapilheira accumulation in the rainy and dry season, besides the medium time return of the litter leaves and litter of the bioma. Was also determined the initial and final concentration of cellulose and lignin for the leaves fractions of the bioma and of the three species with greater VI. The medium density was of 3,372 individuals.ha-1 and area basal of 13.47 m2.ha-1, being identified 2,026 individuals, distributed in 22 species, 20 genera and 12 families. The species with greater VI was Croton sonderianus, Caesalpinia pyramidalis and Aspidosperma pyrifolium. The litter production was of 2.068 Mg.ha-1.year-1, being almost 80 % of leaves. The deposition pick happened in May, in the begin of the dry period, except for Aspidosperma pyrifolium and miscellany fraction. Correlation was not observed with the pluviosidade in the experimental period. The litter of the caatinga returned to the soil, in kg.ha-1, about 31,97 of N; 2,74 of P; 20,60 of K; 60,48 of Ca; 5,38 of Mg and 3,52 of S. Among the three studied species, C. pyramidalis leaves presented the largest amounts of N, P, K, Ca and S, while Mg was more elevated in the A. pyrifolium leaves. The nutrient efficiency use by the vegetation was small, suggesting that the primary productivity of the studied caatinga is not limited by the readiness of the analyzed nutrients. The largest decomposition rate happened in C. pyramidalis and the smallest in C. sonderianus, with larger degradation happening in the beginning of the rains, being almost null in the dry period. The losses were better correlated with the relationship C/N and the temperature, but not with the pluviosity. The potassium was the element with larger and faster liberation in all the treatments, arriving more than 88 % soon in the rainy period begin. The time to degrade half of the serapilheira varied of 174 to 349 days, for C. pyramidalis and C. sonderianus, respectively. The litter accumulation was of 6.286 Mg.ha-1, being 60 % larger in the dry period than in the rainy season. The medium return was of almost 20 months for the litter leaves and 36 months for the caatinga litter.