RELEASE PATTERN FOR POTASSIUM FROM DECOMPOSING FOREST NEEDLE AND LEAF-LITTER - LONG-TERM DECOMPOSITION IN A SCOTS PINE FOREST .9.

A general pattern for the dynamics of K in decomposing leaf and needle litters is described, based on 139 litter decomposition studies carri ed out in forests of northern and central Europe and the northern Unit ed States. We distinguished an initial phase of fast changes in K conc entration and a later one in which the litter was close to humus and a ll K appeared to be immobile. In the initial phase the rate of change in K concentration was related to the initial K concentration: the hig her the initial concentration, the faster its decrease and the faster the quantitative release of K. For litters with particularly low initi al K concentrations, an increase in concentration was observed from th e very start of decomposition. In the late phase a slight increase in concentrations was observed. After ca. 60% accumulated mass loss, K co ncentrations approached similar levels in various litter types, irresp ective of the litter type and initial concentrations. We also estimate d a theoretical equilibrium state at which no change in K concentratio n should be expected. According to our estimates these equilibrium con centrations ranged from approx. 0.8 mg/g dry mass of litter for Scots pine to approx. 1.2 mg/g dry mass for deciduous litter types. The esti mate of K concentration in Scots pine litter in late decomposition sta ges was very close to that measured in the humus at the same site. Bas ed on the wide variety of litter types and sites studied we conclude t hat the pattern suggested for K dynamics in decomposing litter holds a t least for European coniferous forests north of the Alps and the Carp athians.