Invasive species can alter soil nutrient cycling pathways, disrupting plant growth and reproduction, but trajectories of ecosystem recovery after the removal of invaders are still relatively poorly understood. The invasive nitrogen-fixing legume kudzu, Pueraria montana var. lobata (Fabaceae) (Willd.), is known to increase soil nitrogen (N), potentially facilitating growth or native weeds or colonization by other introduced species. To understand the impacts of kudzu on soil nitrogen of forest communities in northern Mississippi, I asked how kudzu alters N availability in the soil and how long this effect persists after it is removed. I measured standing pools of nitrate, nitrite, and ammonium in soil as well as the net N mineralization, net nitrification, and inorganic nitrogen within the soil, as well as the total organic carbon (TOC) content on infested, control, and removal sites. Removal occurred through a variety of management techniques such as prescribed burn, herbicide, or a combination of the two, and occurred from 3-29 years prior to this study.
Results/Conclusions
Nitrate concentrations were significantly higher in infested sites compared to control sites but no other measure of nitrogen or carbon differed significantly. There were no significant differences in any measure of nitrogen or carbon availability or ecosystem function with time since removal or among removal methods. Although nitrate was elevated during active kudzu infestation, the results suggest this enrichment effect is rapidly lost after kudzu removal in soil in northern Mississippi. This result contrasts with previous studies of fertilization treatments, where soil nitrogen levels remained elevated after treatments were discontinued. These finding may shed light on the nitrogen cycle and its effects when paired with a nitrogen fixer. It will help forest managers determine the best removal strategy needed for kudzu without residual effects within the soil.