Alternative strategies of carbon-nitrogen use for native and invasive forest shrubs of the Eastern United States

Background/Question/Methods

Plant invasions have altered plant communities and ecosystem processes worldwide. Recent meta-analyses indicate that invasive species often have greater productivity compared to co-occurring natives. Because productivity is closely tied to plant nitrogen (N) use, high invader productivity should be closely associated with N use strategy. Although a number of studies have compared leaf-level N use strategies between natives and invaders to explain greater carbon (C) gain of invaders, few studies have examined both above and belowground processes to explore how whole-plant C and N uptake and use strategies differ between invasive and native plants, especially for woody species.

In 2011, we conducted a survey of a suite of root and shoot traits in 24 species of 14 non-native and 10 native forest shrubs of the Eastern U.S. in a common garden in Syracuse, NY. We measured May-November root growth (total length), specific root length (SRL; length per unit dry mass), root tissue density (dry mass per unit root volume), and soil C and N concentration, determined at a two-month interval for three individual plants for each species.  Root growth was measured with the ingrowth core method. Total leaf area and leaf chemistry (C, N) were also measured every two months from July to November and from May to November at a two-month interval, respectively. 

Results/Conclusions

Non-native shrubs were more productive than natives over the growing season for both leaf and root growth. Non-native shrubs had higher SRL and leaf N concentrations but lower leaf N resorption rates and root N concentrations than native shrubs. Soil N concentration underneath non-native shrubs was significantly lower than that of native species. Our results suggest that invading shrub species have a greater capacity to take up soil N compared to native shrubs, which allows invaders to compensate for their greater N loss during leaf senescence and sustain greater leaf N concentrations and photosynthetic rates during the growing season. The results also suggest that there is an underlying tradeoff between shrub root production and leaf nutrient resorption. Different resource use strategies between native and non-native species should influence ecosystem processes, altering soil C and N cycling.