Global warming effects on forest soil processes

• Applicant: Professor Dr. Werner Borken
• Subject Area: Soil Sciences
• Term: from 2018 to 2022
• Project identifier: Deutsche Forschungsgemeinschaft (DFG) - Project number 397643203

Soil organic matter (SOM) dynamics are one of the least understood responses of terrestrial ecosystems to global warming. Rising temperature increases SOM decomposition and CO2 efflux from soil to the atmosphere of N2O. The availability of nutrients such as nitrogen (N) and phosphorus (P), and thus their interactions with the soil C cycle, can increase as well. The temperature effect on soil C and nutrient cycling is however not necessarily linear over time. Warming can gradually deplete the pool of decomposable SOM. Microbial physiology can adapt to warmer conditions and to potential changes in the stoichiometry of C:N:P of organic matter over time. Therefore, the long-term response of soil C and nutrient cycling can differ substantially from the short-term response. In the soil warming experiment Achenkirch, we have increased the soil temperature by 4°C since 2004. The goal is to prolong the warming experiment for further 3 years as we observed a strong sustained increase of soil CO2 (~ 40%, 2005-2017) and N2O efflux (~50%, 2005-2009). Such a strong and persisting increase in soil CO2 efflux has not been observed in forest ecosystems so far. Our experiment is one of a mere handful of studies world-wide monitoring the effects of soil warming for more than 10 years. We will continue the soil CO2 efflux survey and asses how long-term warming affects soil N2O fluxes. The long-term dataset will allow quantifying the warming induced soil C loss by (i) budgeting of C fluxes (15 years of soil CO2 efflux vs. C input) and (ii) C pool comparisons (C stock 2004, 2013, and 2019). We will assess the radiocarbon (14C) signature of fine roots and soil and apply a new generation 14C model to estimate the turnover of fine roots and soil C. Warming effects on the leaching of dissolved organic and inorganic C will be evaluated. By combining all data, we will come up with a long-term scenario of soil C dynamics under elevated temperature for this calcareous forest soil.Interactions between soil C, N, and P cycles will be assessed with a special focus on the root/soil interface (rhizosphere). Mycorrhization and the structure of fungal decomposer communities will be monitored. We will further test for warming effects on root exudation. Additionally, we will follow warming effects on in-situ soil C, N and P availabilities and fluxes, and related microbial processes. These data will enable us to analyze shifts in the C:N:P stoichiometry of roots, soil, microbial biomass, and soil enzymes as triggered by seasonal variations and soil warming, providing a proxy of shifts in element limitation of the soil microbial communities. The Achenkirch soil warming experiment enables a meaningful forecast of organic C and nutrient stocks and cycling in Alpine forest soils on a warmer earth.

• DFG Programme: Research Grants
• International Connection: Austria
• Co-Investigators: Dr. Andreas Schindlbacher; Professor Dr. Wolfgang Wanek