Associations between the invasive shrub Lonicera maackii and native tree species influence the soil microbial community

Background/Question/Methods

Invasive species are significant drivers of global environmental change, but their impact on ecosystem processes is often not uniform.  Invasive plants may have variable effects within a given environment depending on their interactions with the dominant native species, adding another layer of complexity to our understanding of invasive species impacts.  Little research has examined such species-species interactions.  Savanna trees with non-overlapping canopies offer a unique opportunity to assess changes in soil processes associated with individual trees that occur as a result of interactions between an invasive species and different native trees species.  The objective of this study was to examine the impact of Lonicera maackii on the microbial community under three dominant, native tree species, Fraxinus quadrangulata, Quercus muehlenbergii, and Carya ovata, in a savanna in central Kentucky.  The soil microbial community structure was measured using phospholipid fatty acid analysis (PLFA) and non-metric multidimensional scaling (NMS).  Results were linked to concurrent studies examining the effect of L. maackii on soil physicochemical properties, nutrient cycling, and decomposition processes that have revealed variable interactions between the invasive shrub and the native tree species.  An examination of the soil microbial community may help to reveal a possible causal mechanism for these observations.

Results/Conclusions

Ordination analysis showed that patterns in microbial community composition were strongly influenced by the presence of L. maackii under C. ovata and Q. muehlenbergii, but not under F. quadrangulata.  The bacterial:fungal ratio was altered by the invasive shrub in a variable manner, with the ratio increasing under L. maackii shrubs under C. ovata and decreasing under L. maackii under the other two species.  Seasonal increases in N mineralization and nitrification were also observed in soils influenced by L. maackii under C. ovata but not under the other two species.  Concurrent studies have also shown that L. maackii decomposition is rapid, but again varies by location, with L. maackii litter breaking down more rapidly under C. ovata than the other two species.  Shifts in the microbial community structure under L. maackii under C. ovata may help to explain some of these observed differences in nutrient cycling and decomposition processes.  If the effects of invasive plant species on certain ecosystem processes are strongly influenced by their association with different native species, this could suggest the need for a more nuanced understanding of the vulnerability of ecosystem processes to invasions of L. maackii and potentially other invasive species.