Riparian invasion of Lonicera maackii influences throughfall chemistry and rainwater availability

Riparian forests are a functionally important interface between terrestrial and aquatic communities, facilitating the transfer of subsidies that support aquatic biota and ecosystem processes. Invasion of the non-native shrub Amur honeysuckle (Lonicera maackii) in forests of the Midwestern United States has resulted in the formation of a dense monospecific shrub-layer along many headwater streams, substantially altering both the composition and structure of riparian plant communities. We investigated the effects of L. maackii on the chemistry of throughfall (rain that has passed through a plant canopy) in a riparian forest. During the growing season of 2015, throughfall collections were made in areas with no plant canopy (Open), a native forest canopy (Upper canopy), and within the forest but immediately under L. maackii shrubs (Honeysuckle). The Honeysuckle treatment intercepted 28–64% more throughfall compared to the Upper canopy treatment, resulting in lowered throughfall volume under the shrubs. The Honeysuckle treatment had substantially greater total carbon and total organic carbon concentration in throughfall compared to other throughfall treatments (P < 0.01). Total nitrogen and dissolved nitrogen deposition was up to 66% reduced under Honeysuckle treatments compared to a 45% reduction from Upper Canopy collections. In summary, these findings contribute to the growing scientific literature demonstrating that invasion by the exotic shrub L. maackii can capture incoming rainwater and alter the chemistry of throughfall, impacting cross-system nutrient subsidies and riparian function.