Anthropogenic carbon emissions have increased atmospheric carbon dioxide, altering stability of ecosystem processes. Decomposition recycles carbon from dead plant material, where it’s either incorporated into biomass or released into the atmosphere. Microorganisms facilitate decomposition by releasing enzymes which catalyze reactions responsible for cycling nutrients. One of the biggest threats facing decomposition in forested ecosystems is species introductions. In the Midwestern US, the invasive shrub, Amur honeysuckle (Lonicera maackii), has overtaken many forests and is likely altering decay dynamics and the destiny of carbon within the region. Thus, monitoring decay dynamics under pressure of honeysuckle invasion is essential to understand nutrient cycling in this region. To examine this problem, we placed blocks of native Quercus rubra and economically important Pinus radiata in a honeysuckle invaded forest for one year and calculated the decay rate to determine environmental and enzymatic drivers of decomposition. We measured size and abundance of honeysuckle shrubs within a meter radius of the decaying blocks as well as environmental variables of moisture and canopy coverage to determine if these factors altered decay rate. We also measured the enzyme activities of β-glucosidase, phosphatase, leucine aminopeptidase and phenol oxidase using oxidative and hydrolytic reactions as a proxy for nutrient turnover.
Results/Conclusions
Larger honeysuckle shrubs increased phosphatase and β-glucosidase activities in pine and oak wood and increased leucine aminopeptidase and phosphatase activities in the pine wood. Phenol oxidase activity increased on oak wood with larger honeysuckle as well. This suggests that honeysuckle is increasing the rates of nutrient turnover directly. Larger honeysuckle shrubs increased moisture of the decaying wood without contributing to differences in canopy coverage. Additionally, β-glucosidase and leucine aminopeptidase were higher with increasing wood moisture, suggesting that honeysuckle indirectly increased rates of nutrient cycling. Phosphatase activity increased with moisture on P. radiata but decreased with moisture on Q. rubra wood. This may be because the microorganisms were moisture limited on the recalcitrant P. radiata wood but were able to release phosphorus more readily from the more labile Q. rubra wood. Together, these results indicate that honeysuckle is priming native woody debris for faster decomposition and therefore increasing rates of nutrient turnover, despite not directly increasing decay rates. These changes could become especially important in later stage decay where there will likely be perceptible differences in decay rates as altered by honeysuckle. Consequently, to ensure effective carbon mitigation management strategies, monitoring decomposition of woody material in invaded forests is essential.