Plant-soil interactions drive GHG dynamics in organic soils under variable water tables: a case study with poplar

Abstract. Organic soils provide a substantial capacity for carbon storage both in below- and above-ground biomass, but they are also a significant contributor to natural terrestrial Greenhouse gas (GHG) emissions. Organic soil melioration, carried out to increase the primary productivity, often leads to increased CO₂ emissions. By monitoring a controlled environment, it is possible to determine how organic soil management practices influence the carbon cycle, including plant vitality and productivity, and consequently shape future carbon sequestration potential.

The aim of this study was to develop a system under semi-controlled conditions to assess the impact of different groundwater levels on GHG emissions, accumulated biomass, and tree vitality. We conducted experiments in semi-controlled conditions to determine the effects of different groundwater levels (-2 cm; -15 cm; -25 cm; -35 cm) on CH₄ and CO₂ emission, soil chemical analyses, and plant morphological (biomass, root and leaf area, shoot length) and physiological (leaf chlorophyll a and b content) parameters. Temporal and diurnal variation strongly impacted GHG fluxes due to the changes in temperature, moisture, and plant growth activity. During soil temperature extremes, extremely high CH₄ emissions occurred at a -2 cm groundwater level. Higher plant productivity had a greater influence on GHG fluxes: it decreased both CH₄ and CO₂ emissions during the day compared to bare soil. Therefore, the autotrophic respiration rate increased with increased productivity, but the primary determinant was heterotrophic respiration.