Changes in Water-Soluble Nitrogen and Organic Carbon in the Post-Fire Litter Layer of Dahurian Larch Forests

Boreal forests account for one third of terrestrial carbon stock. Wildfires are an important perturbation of this carbon pool, affecting in particular the litter layer. After forest fires, the litter layers may possess shifting chemical property and decomposition dynamics due to the changes in post-fire vegetations succession and abiotic factors. We measured water-soluble organic carbon (WSOC) and water-soluble nitrogen (WSN) in the litter layers of Oi and Oe horizons in boreal forests along a gradient of fire history in northeastern China. We found that WSOC and WSN concentrations in the Oi layer were higher than those in the Oe layer. The concentrations were markedly altered by fires and showed different responses to the ecological succession. The time since fire had significant positive correlations with WSOC in Oi and Oe layers. Interestingly, the distance-based redundancy analysis and the structural equation model analysis indicated that factors additional to the time since fire also strongly influenced the litter water-soluble matter (WSM) properties. Biotic factors were more strongly correlated with the litter WSM properties in the Oe layer than in the Oi layer. Although biotic factors contributed less than abiotic factors to the WSM properties, they still play significant roles in litter WSM in burned area. Our results show that manipulating biotic factors can be an important management strategy for litter WSM restoration, which can assist the overall ecological restoration in burned forests faced with the increasing danger of wildfires in the changing global climate.