Seasonality and nitrogen supply modify carbon partitioning in understory vegetation of a boreal coniferous forest

E-ISSN： 1939-9170|97|3|671-683

ISSN： 0012-9658

Source： Ecology, Vol.97, Iss.3, 2016-03, pp. : 671-683

Disclaimer: Any content in publications that violate the sovereignty, the constitution or regulations of the PRC is not accepted or approved by CNPIEC.

Previous Menu Next

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.