Soil C and N dynamics in a Mediterranean oak woodland with shrub encroachment
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Background and aims
Intensive land use has led to degradation and abandonment of Portuguese oak woodlands, and subsequent shrub encroachment may have altered the spatial heterogeneity of soil C and N pools. The aim of this study was to evaluate the effects of shrub invasion on soil C and N dynamics in an oak woodland in Southern Portugal.
Soil was sampled beneath and outside scattered Quercus suber L. canopies, considering non-encroached areas and areas encroached by shrubs (Cistus ladanifer L. or Cistus salviifolius L.).
The spatial heterogeneity of soil C and N contents was mainly associated with tree presence. Outside tree canopies, the labile C pools were larger (mainly beneath C. ladanifer) and C cycling was faster in encroached areas than in non-encroached areas. Net and gross N mineralization and urease and protease activities were also higher in encroached than in non-encroached areas; however, the metabolic quotient and the Cmicrobial/Corganic ratio were not significantly affected. Beneath the tree canopy, significant effects of encroachment included a small increase in soil labile C and the enzymatic activity beneath C. ladanifer.
The results indicate the potential capacity of shrub encroachment to accumulate soil organic C in the long term. The rate of soil C and N turnover promoted by shrub encroachment may depend on the Cistus species present.
Keywords15N isotope dilution technique Gross N mineralization Hot water-soluble C Particulate organic matter Soil respiration
The study was conducted within the activities of the Centro de Estudos Florestais (FCT), Instituto Superior de Agronomia. Part of the funding for the isotopic ratio mass spectrometer was obtained from the European Regional Development Fund (EU). The first author is grateful to the Portuguese Science and Technology Foundation for financial support for this postdoctoral research (SFRH/BPD/27067/2006). We thank Paula Simões for assistance in sampling design and Paulo Marques for help with fieldwork. We also acknowledge laboratory staff in the Departamento de Ciências do Ambiente (Instituto Superior de Agronomia) for technical assistance with analytical work. The authors also thank Ana Carla Madeira for comments on the text of an earlier version of the manuscript.
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