VARIABILITY OF NITRIFICATION POTENTIALS IN PATCHES OF UNDERGROWTH VEGETATION IN PRIMARY SCOTS PINE STANDS

We investigated whether the distribution of undergrowth species could explain small-scale spatial variability of nitrate production in prima ry Scots pine stands. This was done by measuring the nitrification pot ential, i.e. the accumulation of NO3--N in homogenized samples of the ectorganic layer, in vegetation patches that consisted of single speci es. These were the grass Deschampsia flexuosa and the dwarf shrubs Emp etrum nigrum, Vaccinium myrtillus and Vaccinium vitis-idaea. The nitri fication potential varied extremely among the vegetation patches (CV = 142). This variability was observed for all undergrowth species. Henc e, we found no indications that the chemical composition of the plant species, e.g. the relatively high content of polyphenolics and terpeno ids of the dwarf shrubs, was important as a regulator of the nitrifica tion process. The nitrification potential was not significantly correl ated with NH4+-N, pH or moisture and was only poorly predicted by the N mineralization potential (R(2) = 0.157). Thus, differences in the ni trification potential between the patches could neither be explained b y the composition of the undergrowth vegetation nor by the availabilit y of NH4+-N.