Sustained production of dissolved organic carbon and nitrogen in forest floors during continuous leaching

The release of dissolved organic matter (DOM) in forest floors is a dynamic component of organic carbon transformations in forest soils. The biogeochemical processes driving the production and release of dissolved organic carbon and nitrogen (DOC and DON) in forest floors are strongly affected by hydroclimatic conditions during rainfall events. We conducted an exhaustive percolation experiment to examine the pool size and sustained production of mobilizable DOC and DON in Oi, Oe and Oa layers of spruce, larch and beech forest floors. The percolation experiment with small reconstructed soil columns was conducted at 5 and 15 °C for 25 days with a percolation volume equal to 36 mm d− 1, adding up to a total percolation volume of 900 mm. Percolates were collected at an interval of 5 days and analyzed for DOC and DON. Simultaneously to the periodic analysis of percolates, the CO2 release was measured. The sustained release of DOM during the last leaching period from day 20 to 25, after 720 mm of percolation, was defined as the production rate of DOM. The cumulative release of DOM was large: in case of the 15 °C treatment, the total amount of DOM extracted for 25 days was on average 1.6% and 2.2% of the total C and N stock, respectively. The largest cumulative release of DOM and CO2 was observed for the beech samples. The ratio of cumulative CO2/cumulative DOC release ranged from 1 to 3 for Oi and Oe samples but was