Deposição, acúmulo de serrapilheira e biota do solo em diferentes estágios de regeneração no Núcleo de Desertificação do Seridó/PB.

Abstract

This work aimed to evaluate the litter deposition and accumulation process and the dynamics of nutrients and edaphic fauna in three areas of caatinga in different successional stages. In each area, 24 1m² collectors were installed to assess litter deposition (fractions and total). To evaluate the litter accumulation, eight samples were collected monthly, during 12 months, in each area with the aid of a metal template (0,5 m x 0,5 m). The contents of macronutrients were determined in all litter fractions. To evaluate the edaphic macrofauna, in each area, eight "Provid" traps were installed and the alcohol-wet biomass of the main groups was determined, and for mesofauna, eight soil samples were taken with the help of metal rings (5,0 cm in diameter and 5,0 cm in height), with extraction in Berlese-Tulgren apparatus. Organisms were identified at the order level and diversity and evenness indices were calculated (Shannon and Pielou). Litter deposition was continuous in the three areas evaluated, and greater in the more advanced stage of regeneration, due to the greater size and density of the vegetation. Production was higher at the end of the rainy season and the beginning of the dry season. The leaves fraction was predominant in all areas. As for litter accumulated on the soil, it was concluded that the branches and leaves fraction were predominant, the greatest accumulation occurred in the advanced stage of regeneration, tending to accumulate more on the soil in the dry period. The concentration of elements (N, P, K, Mg and S) in litter deposited and accumulated in the soil were higher in the advanced successional stage. Nitrogen, calcium and potassium were the most abundant elements in all fractions. The leaves and branches presented, the highest and the lowest, concentrations of most nutrients, as it is the most active part of the plant. When comparing the concentrations of macronutrients in the litter deposited and accumulated, it was noticed a decrease in the concentration of all nutrients with the exception of calcium. Macronutrient contents were higher in the rainy season. The initial stage was the one with the highest number of individuals of meso and macrofauna, however for mesofauna, it presented, along with the average stage of regeneration, the lowest Shannon and Pielou indices. The advanced stage showed more diversity and evenness due to the higher Shannon and Pielou index. As for the behavior of macrofauna, the highest diversity index was recorded in the medium stage of regeneration, and the lowest in the advanced stage, as it recorded greater dominance of some groups. As for macrofauna biomass, at all stages Hymenoptera was the group that presented the highest values, representing on average about 40% of the total biomass. And the middle stage of regeneration had the highest macrofauna biomass. Some chemical attributes of the soil had positive and negative correlations between the meso and macrofauna groups, but in general, the correlations were weak.