DRYSOM · Unraveling long-term soil organic matter dynamics under drought in forest soils and their link to ecosystem properties

Unraveling long-term soil organic matter dynamics under drought in forest soils and their link to ecosystem properties

Severe drought periods are predicted to further increase in Europe. The increasing frequency of drought will affect not only the tree growth but also the capacity of forests to store the CO2 from the atmosphere. While drought effects have intensively been studied for plants, much less is known about their impact on soils. Soils represent a large reservoir of CO2 – larger than the atmosphere and vegetation together – and thus have a crucial role in the CO2 removal and in the climate change mitigation. The proposed project aimed to estimate how reoccurring summer droughts affect changes in the quantity of carbon stored in the soils of forests, where the CO2 can be stored for long periods of time as soil organic matter. Research activities were carried out in a unique long-term irrigation experiment in a dry pine forest (Valais, Switzerland) ongoing since 2003: https://www.wsl.ch/en/about-wsl/instrumented-field-sites-and-laboratories/experimental-sites-in-forests/pfynwald.html#tabelement1-tab2. Specifically, the project objectives were to: (1) quantify the amount of new carbon transferred from the roots and from the fungi associated with the plant roots (i.e. mycorrhizal fungi) into the soils and the losses of ‘old’ organic matter from the soils, by burying small soil bags with different mesh sizes, and relating these changes to the communities of bacteria and fungi living in the soils, (2) determine drought impacts on the long-term storage of organic matter in the soil, how this is affected by soil fauna, and what are the effects on the main sources of organic matter (e.g. foliage, roots and fungi), (3) link the knowledge of soil processes to ecosystem properties measured by collaborating research groups at the Swiss Federal Institute for Forest, Snow and Landscape Research WSL. The use of a long-term experiment, together with novel approaches combining isotopic and DNA analysis, offered a unique opportunity to identify the effects of repeated droughts on the amount and the stability of organic matter in the soils, where CO2 can be stored at long time scales. The obtained results are highly relevant for facing current climate change impacts on forests, representing essential ecosystems both for the environment and for the society.

Data: CORDIS, © European Union