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

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. Management of soils with high organic matter content, particularly through drainage and productivity enhancement, often leads to increased CO 2 emissions. By monitoring in a controlled environment, it is possible to determine how groundwater level and environmental conditions 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 determined the effects of different groundwater levels: −2; −15; −25; and −35 cm. We monitored CH 4 and CO 2 autotrophic and heterotrophic emission, soil chemical analyses, and plant morphological (biomass, root and leaf area, shoot length) and physiological (leaf chlorophyll a and b content indices) parameters. Temporal variation strongly impacted GHG fluxes, while diurnal variation in CO 2 emissions depended on groundwater level, with a distinct day–night response at −35 cm, whereas no groundwater-dependent diurnal response was detected for CH 4 . During soil temperature extremes, extremely high CH 4 emissions occurred at a −2 cm groundwater level. Higher plant productivity had a greater influence on GHG fluxes: it decreased both CH 4 and CO 2 emissions during the day compared to bare soil. Therefore, the autotrophic respiration rate increased with increased productivity, but the primary determinant was heterotrophic respiration. The study demonstrates that groundwater level, together with plant productivity and environmental conditions, jointly regulates GHG emissions in organic soil.