Tino Peplau

Tino Peplau successfully defended his doctoral thesis entitled "Effects of temperature and land use change on soil organic matter dynamics in a permafrost-affected ecosystem" on 17.3.2023 in Hannover. The dissertation was prepared as part of the DFG project "Breaking the Ice - Effects of northward expanding agriculture on soil carbon turnover under changing climate conditions" and supervised by PD Dr. Christopher Poeplau and Prof. Dr. Georg Guggenberger.

Climate change may lead to an expansion of agricultural activity in the global North, which is currently dominated by very carbon (C)-rich ecosystems and soils. In addition, subarctic soils are often frozen all year round (permafrost). Land use changes, such as the clearing of subarctic coniferous forest and subsequent agricultural use, represent a strong intervention in the local microclimate and could lead to an accelerated thawing of permafrost. This could have a very strong impact on soil organic carbon stocks, stronger than land use change on soils without permafrost influence.

With this main hypothesis, the Breaking the Ice project went on a large sampling campaign in the Canadian Yukon Territory to sample paired areas consisting of forest and adjacent agricultural soils (cropland and/or grassland). Both forests with and without permafrost influence were investigated. The Yukon Territory has been used for small-scale agriculture since the gold rush over 120 years ago. In addition to sampling for soil chemistry and physics, soil temperature and litter decomposition were also determined over two years at all sites using buried tea bags. All this was additionally done at a forest site near a geothermal spring to quantify the effect of long-term soil warming on soil organic matter dynamics.

According to Tino's analyses, land use changes on permafrost soils resulted in significant losses of soil organic carbon, while this was not the case for deforestation on soils without permafrost. Moreover, no permafrost was detected on agricultural soils, which was a clear indication of accelerated thawing. Regardless of permafrost occurrence, a 2°C higher soil temperature was found under arable and grassland use than in forest, which also affected litter decomposition, at least in the case of arable soils. In the mostly irrigated and heavily fertilised arable soils, organic matter was converted relatively quickly.

In the warming experiment, Tino was also able to demonstrate clear losses of soil carbon, but not of nitrogen. This was most likely directly microbially fixed during decomposition of the organic matter and thus remained in the system.

All in all, Tino's work impressively demonstrated that both climate change and possibly increasing human activity in the global (sub)arctic can lead to a decrease in carbon stocks, especially in frozen soils. This in turn would exacerbate climate change itself. Sustainable and climate-friendly agricultural development of the global North seems possible, but should consider small-scale local conditions.