Effects of Rhamnus cathartica (common buckthorn) stand age on decomposition

Background/Question/Methods   Many studies have investigated the effects of invasive species on biodiversity, but invasive plants can also directly alter ecosystem processes such as decomposition. Ecosystem changes resulting from invasion may be attributed to distinct physical traits introduced by the invasive. Plant traits can influence litter inputs and soil properties, both of which are important factors affecting biogeochemical processes. Common buckthorn (Rhamnus cathartica) is an exotic invasive shrub that can alter decomposition via inputs of high quality leaf litter and possible modifications to the soil environment (e.g. increased moisture and pH). These effects of buckthorn on decomposition may vary with age due to changes in litter chemistry since plants shift allocation of resources to different plant structures as they age. In addition, species modifications to the soil environment may be magnified as a stand ages. In this study, chemistry of leaf litter from mature and juvenile individuals was analyzed, and respiration rates and soil properties were measured under juvenile and mature buckthorn individuals in the field. It was expected that leaf litter from juvenile and mature shrubs would be chemically distinct and that these differences, along with soil modifications, would be translated into variations in respiration rates between the two age groups.

Results/Conclusions   As expected, leaf litter chemistry did differ between juvenile and mature individuals. Mature leaf litter had significantly (p < 0.05) higher concentrations of calcium, copper, sulfur, and zinc. There was a marginally significant (p = 0.055) difference in sodium concentrations with mature leaf litter having more sodium. Juvenile leaf litter had significantly (p < 0.05) higher concentrations of boron, iron, magnesium, and manganese. Notably, many of these chemicals are cations and metals, which are often linked to changes in soil properties. However, there were no significant differences in field respiration rates or soil properties (moisture, organic matter, pH). Though there are notable differences in the leaf litter chemistry of juvenile and mature buckthorn shrubs, it is unclear how this may impact decomposition. Currently, we are following up this study by separating the effects of litter chemistry from soil properties using microcosms to measure respiration and mass loss of leaf litter from juvenile and mature shrubs. Understanding how decomposition changes with Rhamnus cathartica age will be crucial for predicting effects on forest communities and for improving management.