Temporal and Spatial Patterns in Root Nitrogen Concentration and Root Decomposition in Relation to Prescribed Fire

This study examined the temporal and landscape-scale patterns of root nitrogen concentration [N], root decomposition and N release from decomposing roots in oak-hickory forest ecosystems in southern Ohio. Sampling was conducted in three watershed-scale treatment units with different prescribed burning regimes, and each of these treatment units was divided into xeric, intermediate and mesic landscape positions. Root [N] decreased through the growing season in live roots but increased in dead roots. Root [N] was significantly lower in the xeric landscape positions, but only during the driest parts of the growing season. There was no consistent effect of prescribed burning on live or dead root [N]. Where differences among landscape position were detected, live root [N] was greatest in the most mesic landscape positions whereas dead root [N] was greatest in relatively xeric landscape positions. Overall, an average of 70% of original mass was lost from root litterbags and 80% of total N was released over one year of decomposition, with no significant differences among burning treatments in the instantaneous decay rate (k) or rate of N release. There were no differences among landscape positions in root decay rate or N release, even though prior studies have demonstrated strong landscape-position effects on leaf litter decomposition in similar sites. Overall, mass loss and N release from root litter is rapid in these ecosystems and relatively unaffected by either landscape position or fire frequency.