NUTRIENT DYNAMICS IN SOME DECOMPOSING LEAF AND NEEDLE LITTER TYPES IN A PINUS-SYLVESTRIS FOREST

We investigated the long-term net dynamics of N, P, S, K, Ca, Mg and Mn in decomposing litter. Green and brown needles of Scots pine (P. sylvestris L.) lodgepole pine (Pinus contorta), as well as green and brown leaves of white birch (Betula pubescens) and leaves of grey alder (Alnus incana) were incubated for up to 4 years in a 130-year-old Scots pine forest. The concentrations of N and S increased linearly with accumulated mass loss, also P concentrations increased linearly after an initial leaching. Moreover, the rate of increase in N concentrations appeared to be proportional to the initial concentration. After the increase, N and P concentrations reached a phase in which they remained constant or declined slightly. Concentrations of Mg and K decreased with accumulated mass loss, especially in litter types with high initial concentrations of these elements. For Mn the pattern was similar but less pronounced. The relationship between Ca concentrations and accumulated mass loss was largely negative, resembling a negative X(2) function. Absolute amounts of nutrients decreased linearly with litter mass loss once a net release had started. This applied to all litter types and nutrients with the exception of Mn release from grey alder leaves.