Root Dynamics of Congeneric Native and Invasive Lonicera and Rhamnus

Invasive woody plants, often escaped ornamentals, are recognized as a major threat in forest ecosystems, altering biodiversity and ecosystem processes, however, little is known about how belowground processes influence these changes.  A common trait associated with woody plant invasion is higher carbon gain from earlier bud break.  Through adaptation of the vernal dam hypothesis, we attempt to understand how the relationship between leafing phenology and belowground patterns of root growth influence seasonal patterns of nitrogen uptake in congeneric native and invasive woody plants.  Toward this goal, we established a comparative study examining root dynamics of congeneric native and non-native species of two common genera in Northeastern North American forests, Lonicera and Rhamnus, which show marked contrasts in leafing phenology.  A field plot of 28 potted plants, seven of each species (L. japonica, L. sempervirens, R. frangula, and R. caroliniana) were established at Cornell University in Ithaca, NY.  Using minirhizotron technology and mylar windows, root systems were nondestructively monitored for fine root growth, turnover and lifespan from July 2010 to March 2012.  Additionally, ¹⁵N tracers were used to determine the seasonal physiological uptake and efficiency of fine roots, through a depletion method in intact roots coupled to root respiration.  We hypothesize that invasive individuals will have higher root relative growth rate and faster root turnover, corresponding to higher uptake in nitrogen.  The data from belowground processes will be correlated with data from aboveground leaf demography collected from Syracuse University to obtain a whole-plant perspective on invasive potential.  We expect root processes to be positively correlated with aboveground leaf dynamics, especially during spring leaf-out when plant nutrient demand is greatest.  Characterization of belowground root systems with joint information on aboveground patterns can significantly enhance our understanding of how woody plants are able to acquire resources necessary to outcompete similar native species.