We study how soil carbon (C) and nitrogen (N) cycling processes change in response to global warming and aim to advance understanding of the underlying mechanisms. We work in different scales from field work on climatic gradients in high latitude and high-altitude ecosystems, to controlled mesocosm studies and laboratory incubations.
We aim to better understand soil C and N cycle interactions, like priming effects, and the role of microbes in climate change feedbacks from the terrestrial ecosystems. Including these processes into soil C and global Earth system models would lead to improved predictions of climate change feedbacks, and our future climate. Our group is based at the Department of Forest Sciences, so forest soils are our focus, but we also study agricultural soils. Our more practical research aims at quantifying the effects of different forest and agricultural management methods on soil C stocks and soil greenhouse gas fluxes. We aim to develop novel management options for increasing C sequestration in soils and minimizing greenhouse gas emissions from agriculture and forestry.
We study the CO2 emissions from soils under warming climate by combinations of soil translocation experiments, field warming experiments and laboratory incubations. We aim to understand the mechanisms underlying enhancing microbial responses to warming (Karhu et al., 2014). Recently our focus has shifted from just measuring CO2 fluxes and SOC losses to also quantifying what remains in the soils after the C has cycled through microbes. Kristiina Karhu’s Academy Research Fellow project (Unravelling the mechanisms of the soil “microbial carbon pump” – soil C sequestration under global change (UNCAP), ongoing until February 2025) has focused on changes in microbial carbon use efficiency (CUE) and dead microbial residues in response to passive warming by soil translocation. We measure amino sugars as indicators for microbial residues in soil.
In a warming climate not only the temperatures change, but both the frequency and magnitude of disturbances like forest fires, insect damages and droughts are predicted to increase. We have studied the effects of these on soil C stocks, soil C and N cycling and greenhouse gas emissions in different ecosystems. We are currently focusing on the effect of storm and insect damages on soil C stocks in forests (work by Maiju Kosunen), and drought effects in agricultural soils (by Doctoral Researcher Xuhui Luo). In addition, different harmful substances that end up in soils can be a human induced disturbance on the functioning of the ecosystem. We are currently investigating the effect of microplastics on C cycling through microbes.
Historically clearing of forests for agricultural use, has caused losses of C from the soils, and these losses continue due to intensive agriculture, and climate warming that are increasing the SOC decomposition rates. By managing the soils in a sustainable way, it is possible to build back at least part of that lost SOC storage, and contribute to climate change mitigation. We are studying the effects of different agricultural or forest management methods on soil SOC stocks, currently via the Carbon action network. In case of forest management, we are focusing on the continuous cover forestry effects compared to rotational forest management (project of Doctoral Researcher Eva-Maria Roth). We are also interested in the above ground plant diversity effects on soil SOC stocks both in agriculture and forestry applications.
Increasing SOC stocks is difficult under climate change when for example the Finnish agricultural soils are currently losing C at an annual rate of 0.04% (on average). This is the same rate at which we should be increasing the SOC stocks to combat climate change according to the 4 per mil initiative. Reversing this trend would be important, but even stopping the decline is a challenge. For climate change mitigation, there is a need to know the amounts and stability of the C gained in soil by different management options. We are currently focusing on the stability of soil C in different projects, for example the EJP soil funded FREACs project, where our group focuses on amino sugar analyses in order to decipher the role of microbial residues in formation of stable SOC. We also collaborate with Jussi Heinonsalo in the Deep-SOM project.
See the collaboration links at the bottom of the page.
We are studying the mechanisms by which different biochars can reduce greenhouse gas emissions from soil, retain nutrients or stabilize SOC from root exudates or other fresh C inputs in addition to the recalcitrant C contained in the biochar itself. We are focusing on these additional benefits of biochar, since its stability and thus potential to increase soil C stocks is well known, but for example the mechanisms by which biochar retains nitrate (NO3-) are less understood. Our research aims at developing biochars and agricultural management options that include biochar soil amendments that help to reduce the use of external fertilisers, reduce N2O emissions and N leaching from soils. We collaborate closely with the Agrichar research group lead by Priit Tammeorg.
Subin Kalu, who did his PhD on “Long-term effects of biochar as a soil amendment in boreal agricultural soils” in our research group, and defended it in autumn 2022, won two ‘best PhD of the year’ prices for his work.
We collaborate closely with the plant-microbe-soil-interactions group from the same Department of Forest Sciences and are also part of the Institute for Atmospheric and Earth System Research (INAR).