Influência do posicionamento no solo na decomposição de folhas e raminhos de Cistus salviifolius L.

Influence of soil placement on decomposition of leaves and stems of Cistus salviifolius L.

M. P. Simões¹, J. Nunes¹, L. Gazarini¹ & M. Madeira²

 

RESUMO

Estudou-se a influência do posicionamento no solo na dinâmica da decomposição de resíduos de arbustos mediterrânicos, numa comunidade característica de montados do Alentejo, durante um período de cerca de 2 anos. Para o efeito, monitorizaram-se as variações de matéria orgânica e de nutrientes em folhas e raminhos de Cistus salviifolius L. colocados na superfície do solo e incorporados a 10 cm de profundidade, através da técnica dos “sacos de decomposição” A taxa anual decomposição das folhas na superfície do solo (-0,71) foi mais rápida do que a dos raminhos em posição homóloga (-0,17). Esta diferenciação foi também observada para as folhas e raminhos incorporados a 10 cm de profundidade, tendo a taxa sido bastante mais elevada (respectivamente -0,98 e -0,43). A diminuição da matéria orgânica ocorreu em duas fases: uma fase inicial de decréscimo bastante rápido, influenciado principal-mente pela natureza do substrato, à qual se seguiu uma fase de decréscimo muito lento, no qual se fez sentir tanto o efeito do substrato como o da sua localização. A libertação dos nutrientes foi mais influenciada pela composição inicial dos resíduos do que pela localização destes no solo, tendo a libertação sido mais rápida nas folhas do que nos raminhos. As relações lineares inversas observadas entre a MO remanescente e a concentração de N no material residual indicam maiores períodos de imobilização de N nas folhas colocadas na superfície do que nas incorporadas no solo.

 

ABSTRACT

The influence of placement on litter decomposition dynamics was studied in the Mediterranean shrub Cistus salviifolius L. Litter bags containing either leaf or branch were placed at soil surface and others buried at 10 cm depth, in a Mediterranean shrubland of Alentejo, Southern Portugal. Changes in organic matter and nutrient content were assessed over a 2-year period. Decomposition was faster for leaves than for branches, as well as for buried residues than for those placed on soil surface. The annual decomposition rates, k, at surface were -0.71 for leaf and -0.17 for branches, while for buried litter they were -0.98 and -0.43, respectively. Organic matter decrease showed two phases: one initial decomposition phase of fast loss, mainly influenced by litter quality, followed by a very slow phase, influenced by both litter quality and placement. Nutrient dynamics was more influenced by litter initial chemical composition than by its placement, and the release was faster in the residues with the highest initial content, the leaves. The linear inverse relations, determined between remaining OM and N concentration in the remaining material, indicate longer N retention periods in the surface leaves than in buried ones.

 

 

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¹ Dep. de Biologia/ICAM, Universidade de Évora, Apartado 94, 7002-554 Évora, e-mail: mps@uevora.pt

² Dep. de Ciências do Ambiente, Instituto Superior de Agronomia, Tapada da Ajuda, 1349-017 Lisboa