Silent Alarms? Unveiling Destabilization Risk in Terrestrial Ecosystem Carbon Fluxes

Ecosystems are increasingly exposed to the pressures of global change, with climate emerging as one of the most influential drivers. However, the mechanisms leading to increased ecosystem destabilization risk remain poorly understood. In this study, we used eddy-covariance carbon flux measurements (GPP, NEP, and Re) from 65 terrestrial ecosystems across the globe, including forests, shrublands, and grasslands from boreal, temperate and Mediterranean biomes to investigate early warning signals of destabilization by analyzing indicators of critical slowing down (trends in lag-1 temporal autocorrelation and interannual variability) and flickering (trends in skewness and kurtosis). We also examined the influence of climate, nutrients, biodiversity, mycorrhizal associations, and vegetation type as potential drivers of these early warning signals. Our results show no widespread transition toward instability, yet a significant subset of sites displayed rising destabilization risk driven mostly by climate variability. Plant biodiversity failed to buffer against this increasing destabilization risk, whereas dominance by either arbuscular or ectomycorrhizal associations appeared to support resilience in NEP. Importantly, we observed that NEP destabilization correlates with reduced carbon sequestration, highlighting a critical feedback mechanism for the global carbon cycle. This research highlights the urgent need to understand the drivers of the temporal behavior of land C fluxes beyond their annual sums in order to properly assess future carbon-climate feedbacks.