Accelerated leaf decomposition of an invasive shrub (Lonicera maackii) and its relationship to soil biota and leaf chemistry

Background/Question/Methods

Amur honeysuckle (Lonicera maackii) is a non-native deciduous shrub introduced from Asia that is rapidly spreading throughout eastern North America.  Impacts of Amur honeysuckle in native habitats include reductions in the growth and reproductive success of native trees, shrubs and herbs, and a loss of species diversity.  Impacts of Amur honeysuckle to ecosystem function are less well-established.  Using leaf litter of Amur honeysuckle and two native tree species, white ash (Fraxinus americana) and hickory (Carya spp.), we tested the hypotheses that honeysuckle litter would decay fastest and support a microbial community distinct from ash and hickory.  To test these hypotheses, five plots were established within a forested area.  Eight grams of leaf litter from each of the three species were sealed in mesh bags and placed at the plots and then collected in 0, 1, 3, 6, 9, 12 and 18 month intervals to measure decomposition over time.  Phospholipid fatty acids (PLFAs) were extracted from a second set of bags at 0 and 1 months to examine microbial community composition.

Results/Conclusions

Honeysuckle had generally higher initial litter quality than either of the two native species with significantly lower initial lignin concentration (P<0.0001), higher percent nitrogen (P<0.0001), lower C:N ratio (P<0.0001), and higher phosphorus concentration (P<0.0001).  Honeysuckle litter decomposed much more rapidly than the other two species (P < 0.0001).  After 12 months, honeysuckle litter had only 2% mass remaining, compared to 50% for both ash and hickory.  Vastly shorter residence time for honeysuckle litter compared to the two native tree species was due at least in part to differences in litter chemistry.  The differences in litter chemistry were also reflected in microbial community composition.  In a principle components analysis in which 61% of the variation was explained in the first two axes, microbial communities on honeysuckle litter clustered separately from ash and hickory microbial communities at both sampling dates.  The first principle component, by which samples were primarily differentiated, was highly positively correlated with %N (r² = 0.69) and negatively correlated with %C (r² = 0.64).  These results suggest that honeysuckle is accelerating decomposition and nutrient cycling by recruiting specific microbial decomposers via its high litter quality in comparison to native species.