Belowground communities in lowlands are less stable to climate extremes across seasons

Ecological responses to climate extremes vary drastically in different spatiotemporal contexts. For instance, the seasonal timing could be a major factor influencing community responses, but its importance is likely to vary at different spatial settings, such as high or low elevation. Here, we investigate how soil communities at high- and low-elevation sites respond to extreme heat events at different seasons (spring, summer and autumn). We simulated one-week heat events based on site-specific climatic history in several laboratory experiments using 360 field-collected soil cores, and measured the resistance and recovery of two major groups of soil biota: Collembola and fungi. We found that Collembola communities from low elevations showed the lowest resistance to extreme heat in spring and summer, with full recovery only observed in spring soils. However, species-specific analysis using joint species distribution models showed that cold-adapted taxa from lower elevations could not recover completely after extreme heat, suggesting range contractions due to climate extremes. Although fungal communities generally remained stable, pathogens increased and saprotrophs declined following extreme heat. Network analysis revealed that the connectance of negative associations between Collembola and fungi increased in response to extreme heat events, indicating that deleterious fungal species constrained the recovery of certain collembolan species. We provide experimental evidence for how heat events can restructure and destabilize ecological communities depending on spatiotemporal contexts like elevation and seasonal timing.