Release of nutrients and dissolved organic carbon during decomposition of Chamaecyparis obtusa var. formosana leaves in a mountain forest in Taiwan

Forest ecosystems in Taiwan are periodically influenced by
typhoons that cause large amounts of litter input to the soil.
The potential rapid decomposition of such litter under the
warm and moist climatic conditions in Taiwan may lead to
nutrient losses via seepage. The goal of this study was to
investigate the dynamics of C, N, K, Ca, Mg, and dissolved
organic carbon (DOC) during decomposition of Chamaecyparis
obtusa var. formosana leaves in a field study at the Yuanyang
Lake site in N Taiwan. We simulated the effect of a
typhoon by adding about three times the annual aboveground
litterfall (totally 13,900 kg ha–1) as fresh leaves. Litterbags
were taken at 7 dates over 16 months, followed by detection
of mass loss and element composition in the remaining litter.
Aqueous extracts of the remaining litter were analyzed for
DOC and major elements. The properties of DOC were characterized
by fluorescence spectra and by its stability against
microbial decomposition.
The litter mass loss was 35% after 16 months. The losses of
Ca after 16 months from the litter bags were about equivalent
to mass loss (39%), while those of K and Mg reached 86%
and 60% of the initial amount, respectively. From the
13,900 kg ha–1 of litter applied in total, 59 kg K ha–1 and 12 kg
Mg ha–1 were released in the 16 months decomposition
period, most of it in the first 4 months. The total release of Ca
amounted to 69 kg ha–1 but was more evenly distributed
throughout the 16 months of observation. The absolute
amount of N in the decomposing litter increased by 37% while
the C : N decreased from 69 to 34. Extrapolated to the manipulation
treatment, this resulted in a N gain of 36 kg N ha–1
within 16 months.
The leaching of K and DOC in laboratory extractions followed
an asymptotic function with highest leaching from the initial
litter and subsequent decrease with time of decomposition.
On the contrary, the leaching of Ca and Mg reached a maximum
after 2–4 months of incubation. About 2% of the C was
extractable with water from the initially incubated leaves. The
bioavailability of the extracted DOC decreased with litter age.
Our results indicate that the decomposition of large amounts
of litter induces a high risk of K and Mg losses with seepage,
but the risk for N losses is low. The sources of N accumulation
in decomposing litter at this site require further studies. In
the initial phase of litter decomposition, the release of DOC
seems to be an important contribution to mass loss.