Effect of invasive black locust (Robinia pseudoacacia L.) on nitrogen cycle in floodplain ecosystem

• We compare the nitrogen budgets of floodplain under the invasive black locust versus indigenous willow species.
• Black locust ecosystem has higher N-flow rates and N storage than willow floodplain site.
• N-related ecosystem processes are faster under the Robinia stands than under the Salix spp.
• Black locust affects the nitrogen cycle through the N-fixation, high N-content litterfall and rapid litter decomposition.
• Black locust alters the N-cycling that results in the water contamination.

Black locust colonization of floodplains can exacerbate the problems associated with increasing nitrogen inputs into the riparian area and river ecosystem. In this study we compare the nitrogen budgets of two sites of floodplain ecosystem, one is colonized by invasive black locust and the other is forested by the indigenous willow species. Our data report the considerably higher N-flow rates, nitrogen storage and the faster total N-related ecosystem processes in the Robinia site in comparison to the indigenous Salix site of the study floodplain. Black locust affects the nitrogen cycle in the study riparian ecosystem through the N-fixation, high N-content litterfall and rapid litter decomposition that results in the increase of the nitrogen flow into the river and contaminates the water. Black locust appeared to reduce the conservation values of colonized areas and adjacent river. Restoration strategies that remove the black locust from invaded sites and prevent the further invasion will slow down the contamination. However, high availability of nitrogen in soil and soil degradation might have a long-term effect on floodplain ecosystem after the restoration.