Effects of tree species and topography on fine and small root decomposition rates of three common tree species (Alnus glutinosa, Picea orientalis and Pinus sylvestris) in 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 and as ephemeral tissues they are returned to the soil on relatively short time scales. Their decomposition in soil can play an essential role for nutrient cycling and organic matter turnover within ecosystems that are important determinants of plant productivity and ecosystem carbon (C) storage. However, the processes and factors influencing the fine-root decomposition rates in forest ecosystems has been studied less than that of litter shed from the above ground parts of trees. In the present study, we therefore investigated the effects of tree species, topography and soil depth on the decomposition rates of fine and small roots using alder (Alnus glutinosa L.), Oriental spruce (Picea orientalis L.) and pine (Pinus sylvestris L.) tree species. 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. Standard root samples were also placed on the same sites in order to evaluate the effects of microclimate on the root decomposition rates. Alder roots showed the highest decomposition rates, followed by pine and Oriental spruce roots. For each tree species, the root samples placed on south aspect and at lower slope on each aspect decayed faster than that on north aspect and at higher slope. The root decomposition rates decreased with increasing root thickness and soil depth. Among the tree species, initial root litter quality (especially C:N ratio) played an important role on their decomposition rates. In addition to litter quality factor, air temperature in open area and under the stands affected decomposition rates of the standard root samples.