Lonicera maackii (Amur Honeysuckle) is a non-native invasive shrub that poses a significant threat to floral biodiversity across the mid-western United States. Previous research has shown significant reduction in native herbaceous growth and fecundity, as well as, tree seedling survival in areas heavily invaded by L. maackii. However, the competitive mechanisms used by L. maackii against native flora are not fully understood. One potential mechanism could be disruption of the symbiotic relationship between arbuscular mycorrhizal fungi and native flora. We hypothesized that mycorrhizal colonization below L. maackii shrubs would be significantly reduced when compared to control sites without the invasive shrub. Additionally, we hypothesized that the percent of arbuscular structures would be lower under L. maackii shrubs than in control locations. In May, June, and August of 2009, soil samples were collected below L. maackii shrubs and in control sites (locations without L. maackii) in a forest in southwestern Ohio. Roots were picked from the samples and were stained and scored for arbuscular mycorrhizal fungi colonization.
Results/Conclusions In May and August, roots under L. maackii did not have a significantly greater percent total root length colonized than control sites. However, June total root colonization levels under L. maackii were significantly higher than controls. The percent total root length colonized with arbuscules was significantly higher under L. maackii for May, June and August (2.3, 4.1 and 3.8 times higher, respectively). Additionally, the density of arbuscule formation in roots was much higher in L. maackii than native control roots. Contrary to our hypotheses, mycorrhizal colonization was not reduced under L. maackii but was equal to or significantly greater than colonization in control sties. The high arbuscular formation in L. maackii roots indicates a large benefit to the shrub, with increased nutrient exchange between shrub and fungus. This strong symbiosis between a native fungus and an invasive shrub could play an important role in the invasive success of L. maackii. Additionally, increased arbuscule formation in L. maackii roots compared to native herbaceous plants could provide a competitive nutrient advantage, enabling L. maackii to out-compete native flora.
