Effect of black alder (Alnus glutinosa) admixture to Scots pine (Pinus sylvestris) plantations on chemical and microbial properties of sandy mine soils

Phytomelioration and tree species selection on poor mine soils are important for reclamation and afforestation success. Black alder (Alnus glutinosa), as N-fixing species, is often planted on afforested post-mining barrens as an admixture to improve soil properties and enhance growth of target tree species. Objective of this study was to assess the effect of black alder admixture on chemical, physical and microbial properties of sandy mine soils afforested with Scots pine (Pinus sylvestris). The topsoil samples (0-5 cm) were taken in areas afforested with Scots pine with black alder admixture at 1 m, 2 m, 4 m and 8 m from the black alder rows and measured for texture, maximum water holding capacity (WHC), pH, Corg and N contents. The measured soil microbial properties included microbial biomass (Cmic), basal respiration rate (RESP), N mineralization rate and urease activity (URE). Community level physiological profiles (CLPP) of soil microbial communities were determined with Biolog® Ecoplates. The highest Corg, N, Cmic, RESP, N mineralization rate and URE values were measured at 1 m from the alders row and then decreased rapidly. The influence of alders ranged to ca 2 m-3 m from the alders row depending on the soil property. Soil microbial communities close to the alders row were functionally more diverse than those in soils from larger distances. There were distinct differences in CLPPs between microbial communities from soil at 1 m and 8 m from the alders row wherein those close to the alders were more efficient in degradation of carbohydrates and those at 8 m in degradation of polymers. Results of the study clearly indicate positive influence of black alder on several soil properties crucial for their biological activity and fertility.