DYNAMICS AND STRATIFICATION OF BACTERIA AND FUNGI IN THE ORGANIC LAYERS OF A SCOTS PINE FOREST SOIL

The abundance and micro-stratification of bacteria and fungi inhabitin g the organic layers of a Scots pine forest (Pinus sylvestris L.) were investigated. An experiment using stratified litterbags, containing o rganic material of four degradation stages (fresh litter, litter, frag mented litter and humus) was performed over a period of 2.5 years. Dyn amics and stratification of fluorescent stained bacteria and fungi, ra tios between bacterial and fungal biomass, and relationships with mois ture and temperature are described. Average bacterial counts in litter and fragmented litter were similar, i.e., approximately 5 x 10(9) bac teria g(-1) (dry weight) organic matter, and significantly exceeded th ose in humus. The mean bacterial biomass ranged from 0.338 to 0.252 mg carbon (C) g(-1) (dry weight) organic matter. Lengths of mycelia were significantly below the usually recorded amounts for comparable tempe rate coniferous forests. The highest average hyphal length, 53 m g(-1) (dry weight) organic matter, was recorded in litter and decreased sig nificantly with depth. The corresponding mean fungal biomass ranged fr om 0.050 to 0.009 mg C g(-1) (dry weight). The abundance of bacteria a nd fungi was influenced by water content, that of fungi also by temper ature. A litterbag series with freshly fallen Litter of standard quali ty, renewed bimonthly, revealed a clear seasonal pattern with microbia l biomass peaks in winter. The mean hyphal length was 104 m g(-1) (dry weight) and mean number of bacteria, 2.40 x 10(9) bacteria g(-1) (dry weight). Comparable bacterial and fungal biomass C were found in the freshly fallen litter [0.154 and 0.132 mg C g(-1) (dry weight) organic material, respectively]. The ratio of bacterial-to-fungal biomass C i ncreased from 1.2 in fresh litter to 28.0 in humus. The results indica te the existence of an environmental stress factor affecting the abund ance of fungi in the second phase of decomposition. High atmospheric n itrogen deposition is discussed as a prime factor to explain low funga l biomass and the relatively short lengths of fungal hyphae in some of the forest soil layers under study.