Protein precipitation by tannins in soil organic horizon and vegetation in relation to tree species

The aim of this study was to compare the concentration of tannins and their capacity to precipitate proteins in the dominant species of ground vegetation (Deschampsia flexuosa (L.) Trin., Pleurozium schreberi (Brid.) Mitt., Vaccinium myrtillus (L.), and Vaccinium vitis-idaea (L.)) and in different layers of the soil organic horizon (litter layer-L, fermentation layer-F, humified layer-H) under silver birch (Betula pendula Roth.), Norway spruce (Picea abies (L.) Karst.), and Scots pine (Pinus sylvestris L.). Total tannin concentrations were also measured in leaves or needles of birch, spruce, and pine. The study site is located in Kivalo, northern Finland, close to the Arctic Circle. Differences in total tannin concentrations in ground vegetation were due mainly to species, with Vaccinium species having the highest values. The influence of the dominant tree species was less important. Protein precipitating capacity was dependent on plant species; the highest values occurred in Vaccinium species and spruce. Because of their relatively high protein precipitating capacity but low total tannin concentration, D. flexuosa and P. schreberi seemed to have more astringent tannins. Concentrations of total tannin and hydrolyzable tannin in the soil organic horizon differed depending on the layer and tree species. In general, the highest concentrations of total tannins were found under birch and spruce in the L layer and the lowest concentrations under pine. Protein precipitating capacity was usually the lowest in the H layer and highest under birch and spruce in the F and H layers. We showed that lignin from rotted pine wood can also precipitate proteins but only small amounts; additionally, lignin can be an important source of error for soil total tannin measurements.