Dr Tom W. N. Walker1,2, Mr Emmanuel L. F. Carino2, Dr Konstantin Gavazov3, Dr Thomas Guillaume2,3, Dr Pierre Mariotte2,3, Dr Constant Signarbieux2,3, Professor Alexandre Buttler2,3, Professor Jake M. Alexander1
1Department of Ecology & Evolution, Université De Lausanne, Lausanne, Switzerland, 2Ecological Systems Laboratory, École Polytechnique Fédérale de Lausanne, Lausanne, Switzerland, 3Swiss Federal Institute for Forest, Snow & Landscape Research, Lausanne, Switzerland
Warming over the past century has caused uphill migrations of many plant species across the globe. Temperature and vegetation composition are both central to the carbon cycle, raising the potential for warming-induced plant range expansions to alter the magnitude of carbon lost from soil to the atmosphere. Despite the possible feedbacks to future climate change, little is currently known about whether plant range expansions will mitigate, or exacerbate, warming effects on soil carbon loss. Alpine ecosystems are of particular relevance to this issue, holding large reservoirs of soil carbon while collectively experiencing an influx of low elevation plants and above-average temperature change. In this study, we used reciprocal transplant experiments and laboratory studies to determine the effects of lowland plant establishment on warming-induced soil carbon loss from alpine ecosystems. We found that even a minor presence (~5% total biomass) of lowland plants facilitated soil carbon loss from the ecosystem under warming. This effect was not apparent under warming alone, revealing the central role of uphill plant migrations in dictating future carbon loss from alpine ecosystems. In isolation, lowland plants had a stimulatory effect on soil microbial activity, which accelerated soil organic matter degradation and, in turn, CO₂ release through microbial respiration. Here, we present this and additional evidence to propose a mechanism through which the arrival of low elevation plants drives soil carbon loss in warming alpine ecosystems.
My work focuses on understanding how climate change affects, and is affected by, the functioning of alpine and arctic ecosystems. Specifically, I borrow approaches from molecular biology, microbial physiology, biogeochemistry and ecosystem science to characterise the interplay between plants, soil organisms and their abiotic environment, and to interrogate this over multiple spatial and temporal scales.