Chemical properties of foliage and O horizons
The highest concentration of N was measured in the leaves of black locust (33.7 mg g-1), followed by black alder (28.1 mg g-1), silver birch (18.6 mg g-1) and Scots pine (12.1 mg g-1) (Table 2). The leaves of black alder had the highest P concentration (1492 µg g-1) significantly higher than in the leaves of birch (1276 µg g-1) and the Scots pine needles (1009 µg g-1). The P concentration in the foliage of black alder (1401 µg g-1) was significantly higher than in Scots pine needles but not than in the silver birch leaves (Table 2). The leaves of N-fixing species were characterized by significantly lower C-to-N and C-to-P ratios but significantly higher N-to-P ratio than the foliage of non-N-fixing trees. The largest C-to-N and C-to-P ratios and the smallest N-to-P ratio were determined in the Scots pine needles.
The O horizons under both N-fixing species contained more N than the O horizons under both non-N-fixing trees (Table 3). However, this was not the case for P. The highest concentration of P in the O horizons was determined under silver birch (851 µg g-1) followed by black locust (808 µg g-1). The P concentration under alder was significantly lower (747 µg g-1) compared with birch but higher than under pine (649 µg g-1). The C-to-N ratio was significantly lower and the N-to-P ratio significantly higher under N-fixing trees than under both non-N-fixing species. However, the C-to-P ratio was significantly higher under Scots pine and black alder than under birch and black locust.