Effects of tree species and topography on root decomposition in Artvin, Northeast Turkey

Fine and small roots of trees are an important part of the terrestrial carbon (C) cycle because they comprise a large fraction of annual net primary production that asephemeral tissues, are returned to the soil on relatively short time scales. Main aim of this study was to investigate the effects of tree species, topography and soil depth on fine and small roots of Alder (Alnus glutinosa L.), Oriental spruce (Picea orientalis L.) and Pine (Pinus sylvestris L.). The root samples collected from two aspects (north and south) and two altitudes (900 m and 1260) on each aspect and were placed into 0-10 cm and 10-20 cm of soil depth. Root decomposition was studied in the field using the litterbag technique for two years. In addition, standard root samples were also placed on two aspects and two altitudes in order to only evaluate the effects of microclimate on the root decomposition. The fine root samples were analyzed for initial nitrogen, phosphorus and potassium concentrations and their concentrations in the root samples were followed after 9 and 15 months decomposition time. Alder root samples showed the highest decomposition rates, followed by pine and Oriental spruce roots. The root samples on south aspect and lower altitudes on each aspect decayed faster than those on north aspect and higher altitudes. The root decomposition rates decreased with increasing root thickness and soil depth. Among the tree species, initial root litter quality seemed to control their decomposition rates. In this study, we found that the alder roots with the highest N concentration decomposed much faster than the Oriental spruce roots with the lowest N concentration. Decomposition rates of the standard root samples were well correlated with temperature either in open area or under the stands. This result illustrates the important point that litter quality may define the potential rates of microbial decomposition but these are significantly influenced by the biotic and abiotic environment in which decomposition takes place.