N dynamics of wooden dowels in the long-term intersite decomposition experiment (LIDET)

Background/Question/Methods: A 10-year Long-Term Intersite Decomposition Experiment (LIDET) in 21 sites from seven biomes found that net N release from leaf litter is dominantly driven by the initial N concentration and mass remaining regardless of climate, edaphic conditions, or biota.  Moreover, fine roots released N linearly with decomposition and exhibited little net N immobilization (Parton et al. 2007). However, it is not clear whether a similar N release patterns occur in the decomposition of wood. The overall objective of this study is to examine N dynamics of above- and belowground wooden dowels in LIDET. Dowels were placed vertically with half of the dowel above- and half belowground on 21 sites where long-term decomposition of leaf and fine root litter was conducted. Each dowel was 1 cm in diameter, 61 cm long, and made by Gonystylus bancanus, a non-decay-resistant tropical tree species.

Results/Conclusions: Unlike leaf litter and roots, decomposing dowels showed different N dynamic patterns across various biomes. Decomposing wooden dowels usually showed net N immobilization at tropical forests when remaining mass of dowels was above 60% regardless of dowel incubation position.  Dowels showed net N release after almost half of initial mass of dowels decomposed.  The extent of net N immobilization of decomposing dowels was much smaller in the tundra, boreal forest, and temperate conifer forest biomes.  Dowels generally released N from the early decomposition phase and did not exhibit net N immobilization in the tundra biome. The N dynamic patterns were similar between belowground and aboveground dowels at most sites. This study suggests that factors such as climate and site conditions as well as initial N concentration influence N dynamics of wood.