Soil Warming Experiment in Lowland Tropical Rainforest (high-temp). SWELTR (high-temp)

Soil microbes form some of the most diverse biological communities on earth, and play a fundamental role in regulating the terrestrial carbon cycle. Perturbation of soil microbial communities by increasing global temperatures could therefore have major consequences for biodiversity and future climate, particularly in tropical forests where remarkable biological diversity coincides with a vast store of soil organic carbon. Here, we show that the diversity of tropical forest soil bacteria and fungi declines markedly with in situ soil warming, with a simultaneous shift in community dominance towards thermophilic taxa. These changes were associated with increased enzymatic activity and adaptation of growth to warmer temperatures, which was estimated to result in CO 2 emissions from soil warmed by 3 to 8ºC to be 25 to 77% larger than from soil at ambient temperature. However, this model-based prediction was exceeded by the observed in situ CO 2 emission increase by 78% to 337% with 3 to 8ºC warming. The additional emissions were explained by abiotic acceleration of enzymatic activity increasing beyond the optimal temperature for microbial growth. Our results suggest that continued warming of tropical forests will have detrimental consequences for soil microbial biodiversity, ecosystem function and future climate.