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Vertical gradients and seasonal variation in stem CO2 efflux within a Norway spruce stand

Tarvainen, Lasse; Räntfors, Mats and Wallin, Göran (2014) In Tree Physiology 34(5). p.488-502
Abstract
Stem CO2 efflux is known to vary seasonally and vertically along tree stems. However, annual tree- and stand-scale efflux estimates are commonly based on measurements made only a few times a year, during daytime and at breast height. In this study, the effect of these simplifying assumptions on annual efflux estimates and their influence on the estimates of the importance of stems in stand-scale carbon cycling are evaluated. In order to assess the strength of seasonal, diurnal and along-stem variability in CO2 efflux, half-hourly measurements were carried out at three heights on three mature Norway spruce (Picea abies (L.) Karst.) trees over a period of 3 years. Making the common assumption of breast height efflux rates being... (More)
Stem CO2 efflux is known to vary seasonally and vertically along tree stems. However, annual tree- and stand-scale efflux estimates are commonly based on measurements made only a few times a year, during daytime and at breast height. In this study, the effect of these simplifying assumptions on annual efflux estimates and their influence on the estimates of the importance of stems in stand-scale carbon cycling are evaluated. In order to assess the strength of seasonal, diurnal and along-stem variability in CO2 efflux, half-hourly measurements were carried out at three heights on three mature Norway spruce (Picea abies (L.) Karst.) trees over a period of 3 years. Making the common assumption of breast height efflux rates being representative of the entire stem was found to result in underestimations of 10-17% in the annual tree-scale CO2 efflux. Upscaling using only daytime measurements from breast height increased the underestimation to 15-20%. Furthermore, the results show that the strength of the vertical gradient varies seasonally, being strongest in the early summer and non-existent during the cool months. The observed seasonality in the vertical CO2 efflux gradient could not be explained by variation in stem temperature, temperature response of the CO2 efflux (Q(10)), outer-bark permeability, CO2 transport in the xylem or CO2 release from the phloem. However, the estimated CO2 concentration immediately beneath the bark was considerably higher in the upper stem during the main period of diameter growth, coinciding with the strongest vertical efflux gradient. These results suggest that higher growth rates in the upper stem are the main cause for the observed vertical variation in the stem CO2 effluxes. Furthermore, the results indicate that accounting for the vertical efflux variation is essential for assessments of the importance of stems in stand-scale carbon cycling. (Less)
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author
publishing date
type
Contribution to journal
publication status
published
subject
keywords
XYLEM SAP, bark conductance, conifer, gas exchange, Picea abies, Q(10), stem growth, stem respiration, BETWEEN-TREE VARIATION, WOOD ASH APPLICATION, LOBLOLLY-PINE TREES, MAINTENANCE RESPIRATION, CARBON-DIOXIDE, WITHIN-TREE, FOREST ECOSYSTEMS, BLACK SPRUCE
in
Tree Physiology
volume
34
issue
5
pages
488 - 502
publisher
Oxford University Press
external identifiers
  • Scopus:84902277583
ISSN
1758-4469
DOI
10.1093/treephys/tpu036
project
MERGE
BECC
language
English
LU publication?
no
id
961aad21-0906-470c-835d-0cd8c7b6ae35 (old id 7515557)
date added to LUP
2014-11-28 12:26:29
date last changed
2016-11-06 04:26:33
@misc{961aad21-0906-470c-835d-0cd8c7b6ae35,
  abstract     = {Stem CO2 efflux is known to vary seasonally and vertically along tree stems. However, annual tree- and stand-scale efflux estimates are commonly based on measurements made only a few times a year, during daytime and at breast height. In this study, the effect of these simplifying assumptions on annual efflux estimates and their influence on the estimates of the importance of stems in stand-scale carbon cycling are evaluated. In order to assess the strength of seasonal, diurnal and along-stem variability in CO2 efflux, half-hourly measurements were carried out at three heights on three mature Norway spruce (Picea abies (L.) Karst.) trees over a period of 3 years. Making the common assumption of breast height efflux rates being representative of the entire stem was found to result in underestimations of 10-17% in the annual tree-scale CO2 efflux. Upscaling using only daytime measurements from breast height increased the underestimation to 15-20%. Furthermore, the results show that the strength of the vertical gradient varies seasonally, being strongest in the early summer and non-existent during the cool months. The observed seasonality in the vertical CO2 efflux gradient could not be explained by variation in stem temperature, temperature response of the CO2 efflux (Q(10)), outer-bark permeability, CO2 transport in the xylem or CO2 release from the phloem. However, the estimated CO2 concentration immediately beneath the bark was considerably higher in the upper stem during the main period of diameter growth, coinciding with the strongest vertical efflux gradient. These results suggest that higher growth rates in the upper stem are the main cause for the observed vertical variation in the stem CO2 effluxes. Furthermore, the results indicate that accounting for the vertical efflux variation is essential for assessments of the importance of stems in stand-scale carbon cycling.},
  author       = {Tarvainen, Lasse and Räntfors, Mats and Wallin, Göran},
  issn         = {1758-4469},
  keyword      = {XYLEM SAP,bark conductance,conifer,gas exchange,Picea abies,Q(10),stem growth,stem respiration,BETWEEN-TREE VARIATION,WOOD ASH APPLICATION,LOBLOLLY-PINE TREES,MAINTENANCE RESPIRATION,CARBON-DIOXIDE,WITHIN-TREE,FOREST ECOSYSTEMS,BLACK SPRUCE},
  language     = {eng},
  number       = {5},
  pages        = {488--502},
  publisher    = {ARRAY(0x8fd1c20)},
  series       = {Tree Physiology},
  title        = {Vertical gradients and seasonal variation in stem CO2 efflux within a Norway spruce stand},
  url          = {http://dx.doi.org/10.1093/treephys/tpu036},
  volume       = {34},
  year         = {2014},
}