AUTHOR=Jochheim Hubert , Wirth Stephan , Gartiser Valentin , Paulus Sinikka , Haas Christoph , Gerke Horst H. , Maier Martin 

TITLE=Dynamics of Soil CO2 Efflux and Vertical CO2 Production in a European Beech and a Scots Pine Forest

JOURNAL=Frontiers in Forests and Global Change

VOLUME=5

YEAR=2022

URL=https://www.frontiersin.org/journals/forests-and-global-change/articles/10.3389/ffgc.2022.826298

DOI=10.3389/ffgc.2022.826298

ISSN=2624-893X

ABSTRACT=<p>The conversion of coniferous forest to deciduous forest is accompanied by changes in the vertical distribution of fine roots and soil organic carbon (SOC) content. It is unclear how these changes affect soil CO<sub>2</sub> efflux and vertical soil CO<sub>2</sub> production, considering changing climate. Here, we present the results of a 6-year study on CO<sub>2</sub> efflux, covering relatively warm-dry and cool-wet years. A combination of the flux-gradient method and closed chamber measurements was used to study the CO<sub>2</sub> efflux and the vertical distribution of soil CO<sub>2</sub> production in a beech (<italic>Fagus sylvatica</italic> L.) and a pine (<italic>Pinus sylvestris</italic> L.) forest in northeast Germany. We observed, on average, similar CO<sub>2</sub> efflux with 517 (±126) and 559 (±78) g C m<sup>–2</sup> a<sup>–1</sup> for the beech site and the pine site, respectively. CO<sub>2</sub> efflux at the beech site exceeded that at the pine site during the wet year 2017, whereas in dry years, the opposite was the case. Water availability as indicated by precipitation was the primary determining long-term factor of CO<sub>2</sub> efflux, whereas seasonal variation was mainly affected by soil temperature, and—in the case of beech—additionally by soil water content. CO<sub>2</sub> efflux decreased more dramatically (-43%) at the beech site than at the pine site (-22%) during the warm-dry year 2018 compared to the cool-wet year 2017. We assumed that drought reduces heterotrophic respiration (R<sub>h</sub>) at both sites, but additionally decreases autotrophic respiration (R<sub>a</sub>) at the beech stand. Soil CO<sub>2</sub> production at the beech site ranged over a greater soil depth than at the pine site, attributed to different fine root distribution. The organic layer and the A horizon contributed 47 and 68% of total CO<sub>2</sub> efflux at the beech site and the pine site, respectively. The seasonal patterns of different CO<sub>2</sub> efflux between both sites were assumed to relate to different phases of tree physiological activity of deciduous compared to evergreen tree species.</p>