Above- and below-Ground Litter Manipulation: Impact on the Retention and Release of Dissolved C and N.

Above and below-ground litter plays an important role in forest ecosystems in terms of nutrient dynamics.  We examined the impact of manipulating above- and below-ground litter on the retention and release of DOC, DON and DIN in the International Long Term Ecological Research (ILTER) site at Sikfokut Forest, Hungary.  Treatments included double annual leaf litter (DL), double wood (DW), removal of annual leaf litter (NL) removal of root inputs (NR) and removal of both leaf litter and roots (NI) plus control plots each replicated three times.  Soil was excavated at 0-5, 5-15, and 15-30 cm in each plot.  We used the mass isotherm method to quantify retention and release.   We hypothesized that with litter removal there would be less retention of C and N on sorption sites compared to those treatments with doubling of litter. Treatment did not impact DOC retention in the 0-5 or 5-15 cm layers (p > 0.05). Release of DOC was significantly different with treatment in the both the 0-5 and 5-15 cm layers (p < 0.01). Ammonium retention and release in the 0-5 cm layer was significantly impacted by treatment (p < 0.001).  Treatment did not impact nitrate retention (p > 0.05) but significantly impacted its release (p < 0.05) in the 0-5 cm layer whereas in the 5-15 cm layer nitrate was not retained at all.  The opposite occurred with DON where it was not retained in the 0-5 cm layer but retained in the 5-15 cm layer.