Warming effects on soil microbial community composition in Nordic salt marsh ecosystems

Plant-microbe interactions control ecosystem functioning. Soil microbial communities regulate nutrient cycling, and by this influence plant productivity and community composition. Wetland plants steer the soil und rhizosphere microbiome through the release of organic compounds and oxygen from roots as well as through the input of litter.

The present study investigates warming effects on soil microbial community composition and activity in two Baltic salt-marsh sites with similar vegetation composition and soil characteristics in relation to plant community composition and soil redox conditions. We hypothesize that soil microbiomes from both sites show a similar response to warming through modulation in taxonomic composition and enzymatic activity.

Soil sods from salt marshes in Sweden and Denmark were transported to the Institute of Plant Science and Microbiology at the University of Hamburg and exposed to a large range of warming treatments in a state-of-the-art experimental facility with automated above and belowground heating (ambient, +3°C, +6°C) over two consecutive growing seasons. We analyzed 16S rDNA and ecoenzymatic activity across different soil depths to investigate the warming response of the microbial community.

In contrast to our hypothesis, a consistent response to warming was missing. Instead, we found that sample origin and soil depth had a strong effect on microbial community composition and ecoenzymatic activity. We observed a stronger warming effect on microbial community composition for samples originating from Denmark, which also showed a stronger differentiation across soil depth. Samples originating from Sweden showed less pronounced depth differentiation, and a weaker response to warming in microbial community composition. However, samples from Sweden had a higher variability of ecoenzymatic activity, suggesting a physiological adaptation to warming rather than an adaptation through changes in taxonomic composition as seen in samples from Denmark. In my presentation, I will further discuss potential effects of vegetation composition and productivity as well as biogeochemical parameters under warming on microbial community composition in salt marsh ecosystems.