Rate of mineralization of needles in Scots pine stand in relation to site and microbiological conditions occurring on dune slopes of contrasting aspects

The aim of the study was to determine the rate of mineralization of needles in a pine stand in relation to site and to microbiological conditions occurring on dune slopes of contrasting aspects. The research was conducted in the old−growth pine forest overgrowing a latitudinally located dune in the Bydgoska Forest (N Poland). On contrasting dune slopes (northern and southern) rate of mineralization of pine needles was investigated in the 2−years experiment (2012−2014) with the litterbag method. Besides, following investigations were conducted in the middle part of both slopes: 1. dynamics of soil moisture and soil temperature were measured at a depth of 3 cm for 18 days during the 2013 growing season (interval of 2 weeks was applied) and 2. populations of bacteria and fungi were determined for all subhorizons of organic soil horizon (Ol, Of, Oh) as well as for a mineral horizon (AEs) of both soils. Weight loss of needles was found to be higher on northern than on a southern slope what was consequently stated for all 4 terms of taking measurements (6, 12, 18 and 24 months after placement of litterbags). The discrepancy has increased with time and after 2 years it equaled 14.7% when the loss was 61.1% for northern and 46.4% for a southern slope. It could be surprising that such differences were found in spite a sunny slope was characterized by stated in a study higher soil temperature. It should have a stimulating effect on mineralization of organic material; however a soil located on a southern slope was also found as much drier. Thus, the periodic deficiency of soil moisture was indicated as a limiting factor for occurrence of both bacteria and fungi on a southern slope due to the numbers of both groups of microorganisms were much lower on the slope than on a northern aspect. Conditioned by more favourable site parameters, higher number of microbial population occurring on a shadow slope could explain higher rate of mineralization of needles stated for the slope aspect. The moisture factor can be of especially high significance for microbial occurrence and activity and thus for litter decomposition just in dry inland dune ecosystems. It was concluded that in relatively monotonous pine forests overgrowing dry and poor in nutrients soils of inland dunes the slope aspect is an agent significantly differentiating both site and soil microbial conditions