Identification

Title

Ecological processes dominate the ¹³C land disequilibrium in a Rocky Mountain subalpine forest

Abstract

Fossil fuel combustion has increased atmospheric CO₂ by ~ 115 µmol mol-1 since 1750 and decreased its carbon isotope composition (δ¹³C) by 1.7-2‰ (the ¹³C Suess effect). Because carbon is stored in the terrestrial biosphere for decades and longer, the δ¹³C of CO₂ released by terrestrial ecosystems is expected to differ from the δ¹³C of CO₂ assimilated by land plants during photosynthesis. This isotopic difference between land-atmosphere respiration (δR) and photosynthetic assimilation (δA) fluxes gives rise to the ¹³C land disequilibrium (D). Contemporary understanding suggests that over annual and longer time scales, D is determined primarily by the Suess effect, and thus, D is generally positive (δR > δA). A 7 year record of biosphere-atmosphere carbon exchange was used to evaluate the seasonality of δA and δR, and the ¹³C land disequilibrium, in a subalpine conifer forest. A novel isotopic mixing model was employed to determine the δ¹³C of net land-atmosphere exchange during day and night and combined with tower-based flux observations to assess δA and δR. The disequilibrium varied seasonally and when flux-weighted was opposite in sign than expected from the Suess effect (D = −0.75 ± 0.21‰ or −0.88 ± 0.10‰ depending on method). Seasonality in D appeared to be driven by photosynthetic discrimination (Δcanopy) responding to environmental factors. Possible explanations for negative D include (1) changes in Δcanopy over decades as CO₂ and temperature have risen, and/or (2) post-photosynthetic fractionation processes leading to sequestration of isotopically enriched carbon in long-lived pools like wood and soil.

Resource type

document

Resource locator

Unique resource identifier

code

https://n2t.org/ark:/85065/d7r78g5f

codeSpace

Dataset language

eng

Spatial reference system

code identifying the spatial reference system

Classification of spatial data and services

Topic category

geoscientificInformation

Keywords

Keyword set

keyword value

Text

originating controlled vocabulary

title

Resource Type

reference date

date type

publication

effective date

2016-01-01T00:00:00Z

Geographic location

West bounding longitude

East bounding longitude

North bounding latitude

South bounding latitude

Temporal reference

Temporal extent

Begin position

End position

Dataset reference date

date type

publication

effective date

2014-04-01T00:00:00Z

Frequency of update

Quality and validity

Lineage

Conformity

Data format

name of format

version of format

Constraints related to access and use

Constraint set

Use constraints

Limitations on public access

None

Responsible organisations

Responsible party

contact position

OpenSky Support

organisation name

UCAR/NCAR - Library

full postal address

PO Box 3000

Boulder

80307-3000

email address

opensky@ucar.edu

web address

http://opensky.ucar.edu/

name: homepage

responsible party role

pointOfContact

Metadata on metadata

Metadata point of contact