Throughfall chemistry and soil nutrient effects of the invasive shrub lonicera maackii in deciduous forests

Invasive species usurp habitat space at the expense of natives, reducing biodiversity and altering ecosystem function. The non-native invasive shrub Amur honeysuckle (Lonicera maackii) is known to have substantial effects on forest structure and biodiversity in Midwestern North America; however, its influence on nutrient cycling is relatively unexplored. We investigated throughfall volume and chemistry, and soil nutrients, under and away from L. maackii shrubs in random locations along transects in three patchily invaded second-growth forests. Significantly lower volumes of throughfall were found under L. maackii canopies than in sites located away from L. maackii. Cation concentrations in throughfall were significantly higher, and in some instances 3 × higher, under L. maackii than in "away" locations. Despite lower throughfall volumes under L. maackii compared to "away" locations, total deposition of cations in throughfall under L. maackii was also consistently higher than in adjacent areas of native forest canopy. In contrast, NH ⁴-N concentrations in throughfall were significantly lower under L. maackii than away, suggesting N transformation and assimilation as rainwater passed through the canopy. No differences were found in soil properties between "under" and "away" locations. In summary, L. maackii significantly reduced the volume of rainwater arriving at the forest floor and altered the chemistry of that rainwater causing an increase in cation concentrations and a reduction in NH⁴-N. These results suggest that L. maackii invasion has the potential to cause significant alterations to nutrient cycling in forests.