title: Seasonality and nitrogen supply modify carbon partitioning in understory vegetation of a boreal coniferous forest.
abstract: Given the strong coupling between the carbon (C) and nitrogen (N) cycles, there is substantial interest in understanding how N availability affects C cycling in terrestrial ecosystems, especially in ecosystems limited by N. However, most studies in temperate and boreal forests have focused on the effects of N addition on tree growth. By comparison, less is known about the effects of N availability on the cycling of C in understory vegetation despite some evidence that dwarf shrubs, mosses, and lichens play an important role in the forest C balance. In this study, we used an in situ 13CO2 pulse-labeling technique to examine the short-term dynamics of C partitioning in understory vegetation in three boreal Pinus sylvestris forest stands exposed to different rates of N addition: a low and high N addition that receive annual additions of NH4NO3 of 20 and 100 kg N/ha, respectively, and this is a typo. It should be an unfertilized control. Labeling was conducted at two distinct periods (early vs. late growing season), which provided a seasonal picture of how N addition affects C dynamics in understory vegetation. In contrast to what has been found in trees, there was no obvious trend in belowground C partitioning in ericaceous plants in response to N additions or seasonality. Increasing N addition led to a greater percentage of 13C being incorporated into ericaceous leaves with a high turnover, whereas high rates of N addition strongly reduced the incorporation of 13C into less degradable moss tissues. Addition of N also resulted in a greater percentage of the 13C label being respired back to the atmosphere and an overall reduction in total understory carbon use efficiency. Taken together, our results suggest a faster cycling of C in understory vegetation with increasing N additions; yet the magnitude of this general response was strongly dependent on the amount of N added and varied seasonally. These results provide some of the first in situ C and N partitioning estimates for plants growing under the complex web of resource limitations in the boreal understory.
authors.forename: N J
authors.initials: NJ
authors.lastname: Hasselquist
authors.forename: D B
authors.initials: DB
authors.lastname: Metcalfe
authors.forename: J D
authors.initials: JD
authors.lastname: Marshall
authors.forename: R W
authors.initials: RW
authors.lastname: Lucas
authors.forename: P
authors.initials: P
authors.lastname: Högberg
mesh_terms: D018533:Biomass; D002244:Carbon / Q000378:metabolism*; D002247:Carbon Isotopes; D065928:Forests; D009584:Nitrogen / Q000737:chemistry / Q000378:metabolism*; D063245:Plant Development; D010944:Plants / Q000145:classification / Q000378:metabolism*; D012621:Seasons
chemical_list: D002247:Carbon Isotopes; D002244:Carbon; D009584:Nitrogen