Year: 2025
Type: conference-paper
Abstract: Soil minerals play an essential role in organic matter (OM) stabilization by reducing its bioavailability thereby slowing its turnover time, and contributing to long-term carbon (C) storage (Lavallee et al. 2019). In humid soils, iron (Fe) and aluminum (Al) oxides are particularly significant contributors to C stabilization (Rasmussen et al. 2018, Salonen et al. 2024). However, Fe oxides are sensitive to changes in soil oxidation-reduction (redox) state. Accordingly, temporary waterlogging leading to anaerobic conditions may result in reductive Fe dissolution, potentially compromising the ability of soils to stabilize OM (Huang et al. 2021). Increased OM availability could thus lead to increased soil CO₂ fluxes, although soil water saturation is traditionally thought to suppress C mineralization (Huang et al. 2021, Moyano et al. 2013. So far, it remains unknown whether the dissolution of Fe-bound OM during temporary anaerobic conditions significantly impacts the C cycle in boreal mineral soils, which are increasingly susceptible to off-season waterlogging due to climate change. We studied the impact of off-season waterlogging on coupled Fe and C dynamics in two distinct arable mineral soils in a 1.5-year long soil monolith experiment. The experiment consisted of three alternating growing and off-seasons, and it was conducted under controlled greenhouse conditions. In total 32 soil monoliths (d 15.2 cm, h 63 cm) were collected from two fields with silty clay and sandy loam texture in southern Finland. During the growing seasons, barley (Hordeum vulgare) was grown in all monoliths while Tall Fescue (Festuca arundinacea) was under sown into half of the monoliths as an overwintering cover crop. After barley harvest, half of the monoliths underwent an excessive irrigation treatment, inducing water saturation for approximately 50 days, while the remaining monoliths served as controls, maintaining soil moisture at 50% water filled pore space. Soil moisture, temperature and redox potential were measured continuously at three soil depths (10, 30 & 50 cm). During the off-seasons, porewater samples were collected from the saturation treatment at the same depths for analysis of dissolved C, nitrogen (N) and Fe. CO2 and CH4 fluxes were measured with a dark manual chamber. After the experiment, the monoliths were destructively sampled for determination of Fe-associated OC (Fe-OC), mineral associated OC and the total C and N contents in the entire soil profile (along with other analyses not detailed here). Waterlogging induced reducing conditions in both soils within one to two weeks which was accompanied by reductive Fe dissolution, especially in silty clay soil. However, the porewater Fe concentrations remained low (max 10 µmol l-1) (Kronberg et al. 2024) and accordingly, repeated waterlogging resulted only a slight and statistically insignificant reduction in soil Fe-OC content in silty clay and no changes in sandy loam soil. No clear differences between the water treatments were found in the total mineral associated OC content in neither soil. Waterlogging altered CO₂ flux dynamics but had no effect on cumulative emissions. No significant CH4 production was observed (Kronberg et al. in revision). In conclusion, our preliminary results suggest that off-season waterlogging at soil temperature +4–12 °C may have minimal impact on the ability of soil minerals to stabilize C in cultivated boreal mineral soils. However, increasing the length or the frequency of waterlogging events could alter this outcome. Additionally, the long-term effects remain to be studied as the combined changes in soil C inputs, soil structure and chemistry of soil constituents could potentially alter soil C sequestration.
Source: ARPHA Conference Abstracts
Authors: Reija Kronberg, Sanna Kanerva, Markku Koskinen, Tuomas Mattila, Mari Pihlatie
Institutions: University of Helsinki, Finnish Environment Institute
Language: English
Subfield: Soil Science
Domain: Life Sciences
Open Access status: diamond
OpenAlex ID: W4410826393