The biodiversity-ecosystem function paradox: why peatland plant diversity fails to protect the peatland carbon sink function under climate change

The future of northern peatlands as long-term sinks for atmospheric carbon (C) has traditionally been thought to hinge on understanding the response to changing abiotic factors, while the complex biological interactions that underpin ecosystem processes – including C dynamics – have been overlooked.  While biodiversity research in other ecosystems suggests that species-rich communities are more stable against environmental pressures – the backbone mechanism being asynchronous responses of species to changes in enviro-climatic conditions – this relationship remains poorly understood in peatlands. Hence, in peatland science, we lack fundamental research that addresses the role of biodiversity in safeguarding the apparent C sink function.

Our research challenges two fundamental assumptions in peatland ecology: first, that species diversity invariably enhances ecosystem stability, and second, that abiotic drivers predominantly control carbon dynamics. Through replacement series experiments with Sphagnum mosses, we show that co-occurring peat moss assemblages offer surprisingly limited insurance against functional collapse under severe drought. These findings strikingly parallel earlier work from a cross-continental study and experimental field work where we show a negligible effect of plant species diversity on ecosystem functioning. Instead, our work highlights fast changes in plant-microbe interactions, which we link to shifts in peatland C cycling. Hence, we propose a paradigm shift in peatland ecosystems: rather than focusing solely on abiotic conditions or plant diversity, we must explicitly consider plant-microbe interactions to understand the response of the peatland C sink to future climate.