Gross and net nitrogen transformation rates and availability in late summer in tall shrub and birch hummock ecosystems of the Canadian low Arctic

Climate change is occurring most rapidly in the Arctic where warming has been twice as fast as the rest of the globe over the last few decades. Arctic soils contain a vast store of carbon and warmer arctic soils may mediate current atmospheric CO2 concentrations and global warming trends. Warmer soils could increase nutrient availability to plants, leading to increased primary production and sequestration of CO2. Presumably because of these effects of warming on shrub ecosystems, shrubs have been expanding across the arctic over the last 50 years, Arctic shrub expansion may track or cause changes in nutrient cycling and availability that favour growth of larger, denser shrubs. This study aimed at measuring gross and net nitrogen cycling rates, major soil nitrogen and carbon pool sizes, and elucidating controls on nutrient cycling and availability between a mesic birch (Betula nana) hummock tundra ecosystem and an ecosystem of dense, tall, birch (B. nana) shrubs. Nitrogen cycling and availability was enhanced at the tall shrub ecosystem compared to the birch hummock ecosystem. Net nitrogen immobilization by microbes was approximately threefold greater at the tall shrub ecosystem. This was in part because of larger microbial biomass nitrogen and carbon (interpreted as a larger microbial community) at the tall shrub ecosystem. Nitrogen inputs via litter were significantly larger at the tall shrub ecosystem and were hypothesized to be the major contributor to the higher dissolved organic and inorganic nitrogen pools in the soil at the tall shrub ecosystem. The results from this study suggest a positive feedback mechanism between litter nitrogen inputs and the enhancement of nitrogen cycling and availability as a driver of shrub expansion across the Arctic.

"Can you ask her to help?" An examination of the factors that promote and discourage prosocial intervention in preschool children

Previous research has examined young children’s ability to detect who would be most likely to provide help to others in a given situation, but little is known about their ability to intervene based on this knowledge in a real-life setting. In the current study, 48 three-year-old children chose between two actors to retrieve an out-of-reach object for the Experimenter; one actor was physically incapable of providing the object (blocked by a tall barrier), and one was capable. Participants’ looking behaviour between the two actors during the study was also recorded and analyzed as an additional, nonverbal measure of their prediction about who would help. Approximately half of the participants in the sample actively intervened on behalf of the Experimenter, but only after a direct request for help was made. Though the other participants did not engage in this helping behaviour, they chose the unblocked actor to help the Experimenter in a subsequent interview. Children also spent more time looking at the unblocked actor. Secondary analyses indicated that shyness prevented many children in the study from asking for help on behalf of the Experimenter from one of the actors. Finally, an unexpected side bias for looking behaviour toward the actors was found that has implications for how the study design could be improved for future research.