Spatiotemporal variability and origin of CO2 and CH4 tree stem fluxes in an upland forest
Date
2021-07-02
Journal Title
Journal ISSN
Volume Title
Publisher
Global Change Biology
Abstract
The exchange of multiple greenhouse gases (i.e., CO2 and CH4) between tree stems and the atmosphere represents a knowledge gap in the global carbon cycle. Stem CO2 and CH4 fluxes vary across time and space and are unclear, which are their individual or shared drivers. Here we measured CO2 and CH4 fluxes at different stem heights combining manual (biweekly; n = 678) and automated (hourly; n > 38,000) measurements in a temperate upland forest. All trees showed CO2 and CH4 emissions despite 20% of measurements showing net CH4 uptake. Stem CO2 fluxes presented clear seasonal trends from manual and automated measurements. Only automated measurements captured the high temporal variability of stem CH4 fluxes revealing clear seasonal trends. Despite that temporal integration, the limited number of automated chambers made stand-level mean CH4 fluxes sensitive to “hot spots,” resulting in mean fluxes with high uncertainty. Manual measurements provided better integration of spatial variability, but their lack of temporal variability integration hindered the detection of temporal trends and stand-level mean fluxes. These results highlight the potential bias of previous studies of stem CH4 fluxes solely based on manual or automated measurements. Stem height, temperature, and soil moisture only explained 7% and 11% of the stem CH4 flux variability compared to 42% and 81% for CO2 (manual and automated measurements, respectively). This large unexplained variability, in combination with high CH4 concentrations in the trees' heartwood, suggests that stem CH4 fluxes might be more influenced by gas transport and diffusivity through the wood than by drivers of respiratory CO2 flux, which has crucial implications for developing process-based ecosystem models. We postulate that CH4 is likely originated within tree stems because of lack of a consistent vertical pattern in CH4 fluxes, evidence of CH4 production in wood incubations, and low CH4 concentration in the soil profile but high concentrations within the trees' heartwood.
Description
This is the peer reviewed version of the following article: Barba, J., Poyatos, R., Capooci, M., & Vargas, R. (2021). Spatiotemporal variability and origin of CO2 and CH4 tree stem fluxes in an upland forest. Global Change Biology, 27, 4879– 4893. https://doi.org/10.1111/gcb.15783, which has been published in final form at https://doi.org/10.1111/gcb.15783. This article may be used for non-commercial purposes in accordance with Wiley Terms and Conditions for Use of Self-Archived Versions. This article may not be enhanced, enriched or otherwise transformed into a derivative work, without express permission from Wiley or by statutory rights under applicable legislation. Copyright notices must not be removed, obscured or modified. The article must be linked to Wiley’s version of record on Wiley Online Library and any embedding, framing or otherwise making available the article or pages thereof by third parties from platforms, services and websites other than Wiley Online Library must be prohibited.
This article was originally published in Global Change Biology. The version of record is available at: https://doi.org/10.1111/gcb.15783.
Keywords
CH4, CO2, greenhouse gas fluxes, temperate ecosystem, tree stem fluxes, upland forest, climate action
Citation
Barba, J., Poyatos, R., Capooci, M., & Vargas, R. (2021). Spatiotemporal variability and origin of CO2 and CH4 tree stem fluxes in an upland forest. Global Change Biology, 27, 4879– 4893. https://doi.org/10.1111/gcb.15783