Five-year decomposition of coarse woody debris in a subtropical forest: Effects of tree species and nitrogen addition

The decomposition of coarse woody debris (CWD) plays a key role in forest carbon and nutrient cycling. Understanding this process has become increasingly important as rising tree mortality leads to substantial CWD production in forests locally and globally. As a low substrate quality plant residue with a high lignin:nitrogen (N) ratio, CWD decay may be more strongly influenced by N deposition than other types of forest litter. This study examined the five-year decomposition dynamics of five dominant tree species—including two broadleaved, two conifer species, and moso bamboo, under control (ambient as 25 kg N ha −1 year −1 ) and N addition (50 kg N ha −1 year −1 added) conditions in a subtropical evergreen forest, southern China. Decomposition rates ( k , year −1 ) were 1.14 and 1.28 times faster in broadleaved deadwood (0.247 and 0.278, respectively) than in bamboo (0.217), while conifers decomposed the slowest (0.016 and 0.062). After five years, mass loss was 41.4 % for broadleaves, 23.3 % for bamboo, and 8.9 % for conifers, with losses occurring mainly in cellulose and hemicellulose fractions. N addition only slightly stimulated the decay of Schima superba (broadleaved species) which had the lowest initial N and lignin content among the five species. After five years of decomposition, only bamboo logs significantly increased soil organic carbon (SOC), partly due to its relatively low CO 2 emissions. Results of this study can help to better predict the ecological impact of tree mortality of different dominant species on the forest carbon balance. Despite the issue of low longevity and high levels of fallen bamboo culms accumulating in large-scale bamboo forest establishment, bamboo CWD-derived organic carbon will not result in additional pressure on carbon emissions, as the case of broadleaved species.