Banca de DEFESA: EDILANE ALICE DE ALCANTARA ASSUNÇÃO

Leaf composition of forest species under different topographic gradients in the Araripe region

Caatinga; leaf decomposition

Leaf decomposition is fundamental to the nutrient cycling process, especially in regions with low amounts of nutrients in the soil and periods of drought severe, like the Caatinga. In these regions, most of the nutrients that maintain the stability and functionality of the system depend on the cycling of nutrients contained in plant biomass. The susceptibility of plant residues to decomposition depends on the its chemical composition and the environmental conditions in which it is inserted. Studies that evaluate the leaf decomposition of species in this forest formation in different altitudes are important for a detailed understanding of the interactions that occur in these environments. Thus, the following hypotheses were tested: i) environments inserted at higher altitudes are more favorable to decomposition due to the higher humidity of these environments, associated with milder temperatures; ii) decomposition should intensify in the humid period, with a greater release of nutrients, even at higher altitudes. casualties; iii) the rate of decomposition of the species must differ, due to chemical composition of plant material and leaf morphology; iv) the lignin contents of the Decomposing plant material can delay the release of nutrients more than the C/N ratio. This research aimed to evaluate the leaf decomposition and the release of nutrients from dominant tree species and correlate the speed of this decomposition with the C/N ratio, the Mn and lignin contents of these species under different topographic gradients in Caatinga, in the Araripe region, in Pernambuco. The dominant species were determined in phytosociological studies previously carried out in the areas of the Chapada do Araripe toposequence. The evaluations took place in areas located in three environments that differ in terms of altitude: Chapada, Slope and Baixada. Decomposition was evaluated by the “litter bags” method at 0, 15, 30, 45, 90, 135, 180, 225, 270 and 315 days. The constant of decomposition (k), T50%, T95% and the release of nutrients N, P, K, Ca and Mg, in addition to C. Additionally, the Pearson correlation of k values with the levels of Lignin, Mn and C/N ratio.  Leaf decomposition intensified in the period with greater rainfall, resulting in greater release of nutrients. In between environments, it was observed that the decomposition in the Chapada occurred at a lower speed to the others, even if inserted in higher altitudes and with rainfall higher. It was possible to identify species that presented different patterns in the decomposition process. In the Chapada, the species Croton limae was less resistant to decomposition, favored by the low C/N ratio and lignin content presented; on Encosta, the species Piptadenia viridiflora stood out for its decomposition and accelerated release of nutrients. This species, despite having a high lignin content, the low C/N ratio presented by the species was the most preponderant factor in the decomposition. Overall, nutrient release rate was better correlated with the C/N ratio, similarly to what was observed with the mass loss. Like this, the dynamics of decomposition is strongly associated with the intrinsic characteristics of each species and its interactions with the environment.