Combination of molecular markers and isotopes for improved assessment of the impact of warming on organic matter cycling in plant-soil systems

Global warming has severe impacts on plant-soil systems. However, the assessment of climate change-driven impacts on organic matter (OM) cycling and storage in plant-soil systems remain largely unknown. Consequently, several warming experiments at field scales like the SPRUCE open-top chamber experiment (Minnesota, USA) and the Blodgett Forest warming experiment (California, USA) were initiated. We combined findings from both sites with laboratory experiments and applied molecular markers as well as bulk and compound-specific isotopes. In peat, the active acrothelm got deeper with warming and thus enabled improved root growth and consequently OM input and cycling. In contrast, lower moisture in deep oxic soils resulted in unfavorable conditions for root growth and therefore less OM input. In-situ decomposition experiments of ¹³C-labeled root litter highlighted that warming has a strong impact on the microbial community composition and degradation of OM, while spatial variability and accessibility of OM in subsoils can have an even higher impact on decomposition of organic matter than warming. Further, laboratory experiments using ¹³C-labeled litter showed that soil microbial communities seem to have a certain temperature optimum, beyond which decomposition of OM might get reduced, again. The chosen combination of different experiments using molecular markers, stable isotopes and isotope-labeling experiments enabled an improved assessment of the impact of future warming on OM cycling in plant-soil systems.