Separation of allelopathic and competitive effects of Lonicera maackii on the native forest annual Pilea pumila

Background/Question/Methods

Recent studies suggest the common forest invader Lonicera maackii possesses allelopathic potential.  However, no research has effectively determined if allelopathic potential of L. maackii is a significant contributor to its invasiveness relative to its ability to compete for below ground resources.  Also, most studies have only focused on single populations of L. maackii in determining any allelopathic effects.  We conducted a full factorial multi-population study to isolate the competitive and allelopathic effects L. maackii on the native forest annual Pilea pumila.  Individual P. pumila plants were grown in pots in the greenhouse in commercial potting soil containing a transplanted 2-3 yr old L. maackii from one of six Ohio populations. Pilea pumila grown alone served as a control. Activated carbon was incorporated into the soil of half the pots from each treatment in order to ameliorate effects of potential allelochemicals and to account for direct effects of carbon treatment.  Independent and interactive effects of activated carbon and L. maackii treatments on final total, above, and below ground biomass of P. pumila was examined using ANOVA.  Identification of potential allelochemicals was investigated by growing 2-3yr old L. maackii alone in pots containing Polydimethylsiloxane (PDMS) laboratory tubing.  Pots with PDMS tubing without plants served as a control. PDMS tubing was removed and extracts from tubing will be analyzed using HPLC to identify bioactive phenolic compounds.

Results/Conclusions

The presence of L. maackii decreased the final total biomass of P. pumila overall by 33%, but populations did not vary in this effect, after accounting for initial size of L. maackii.  Activated carbon increased total biomass of P. pumila in the absence of L. maackii by 44% but there was no benefit of activated carbon when L. maackii was present.  Below ground biomass of P. pumila was more responsive to treatments than above ground biomass.  Final biomass of L. maackii was independent of the presence of carbon.  We conclude that Ohio populations of L. maackii do not vary in their ability to compete for below ground resources or in their allelopathic potential.  The lack of response of L. maackii to activated carbon and its ability to inhibit the positive effects of carbon on P. pumila suggest that L. maackii exerts its effects through a combination of resource competition and allelopathy.