Soil fluxes of mineral elements and dissolved organic matter following manipulation of leaf litter input in a Taiwan Chamaecyparis forest

Forest ecosystems in Taiwan are frequently influenced by typhoons that cause large amounts of litter input to the soil. The rapid decomposition of such litter under the high precipitation and temperature conditions may trigger nutrient losses via seepage. Our goal was to investigate the effects of exceptionally high inputs of Chamaecyparis obtusa var. formosana leaves to the soil on the solute fluxes and concentrations of mineral elements, dissolved organic carbon (DOC) and dissolved organic nitrogen (DON) in a Lithic Leptosol. We simulated the effect of a typhoon by adding the annual aboveground litterfall (4600 kg ha−1) and about 3 times the annual litterfall (13,900 kg ha−1) as fresh leaves in a single event to small manipulation plots. All plots were also subjected to the natural litterfall. Soil solution was collected 4 months before and 15 months following the litter manipulation in 14 days intervals underneath the forest floor with free draining lysimeters and by ceramic suction cups at 60 cm depth. The 3-fold litter addition caused increased fluxes of K, Mg, Ca, and NH4 in forest floor percolates as compared to the 1-fold litter treatment. DOC and DON fluxes also increased, but this was only statistically significant for DON. DON was the dominant form of N both in forest floor percolates and in seepage. The 3-fold litter manipulation increased the seepage fluxes of K, DON, and DOC relative to the 1-fold treatment with largest differences recorded for K, reaching 12.4 kg ha−1 15 month−1. The fluxes of DOC with forest floor percolates and with seepage in both treatments exceeded published values by far. Our results suggest that the decomposition of large amounts of fresh leaf litter may trigger K losses from the ecosystem via seepage, whereas the probability for additional N and DOC losses is moderate. For Ca and Mg, additional losses seem to be rather unlikely.