Lee, MH; Park, J-H; Matzner, E: Sustained production of dissolved organic carbon and nitrogen in forest floors during continuous leaching, Geoderma, 310, 163-169 (2018), doi:10.1016/j.geoderma.2017.07.027
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< 0.2 for spruce Oa. No changes in DOC/DON ratios as a result of percolation amount were detected. The production rates indicated a rapid replenishment of DOM pools after leaching. The Q10 values for the DOM production rates ranged from 2 to 4 and were similar to those for CO2 production. The positive correlation between DOM and CO2 production rates in Oi and Oe samples highlights the importance of microbial activity for DOM release. The pool of mobilizable DOM in forest floors seems large enough to provide a sustained rate of DOM release throughout precipitation events under field conditions although the actual rate of mobilization may vary in the field, depending on antecedent conditions and the duration and intensity of the rainfall event.
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