Lengthening vegetation carbon turnover time across China's forests

Vegetation carbon turnover time (τ_veg) dominates the uncertainty in terrestrial carbon cycle dynamics. Reports have shown that the τ_veg of mature or old-growth forests in North America and Europe has decreased because of faster carbon loss under global climate change. However, the temporal trend of τ_veg in widespread younger forests, which exhibit different growth patterns, remains inconclusive. Here, we consistently revealed a significant overall increase in τ_veg (0.025 ± 0.002 years per year) across China's forests that are characterized by a relatively young forest age structure, using multisource data-model assimilation and long-term network observations. In young forests that receive high nitrogen deposition, increasing levels of CO₂ accelerate vegetation growth, causing it to grow faster than it dies or decomposes, leading to increases in the τ_veg. The effects of forest age on τ_veg dynamics and the high sensitivity of enhanced carbon sinks to τ_veg should be incorporated into future land surface models to ensure that the τ_veg dynamics and their impacts on terrestrial carbon cycling and climate mitigation are accurately assessed. Our results also provide valuable insights for forest management aimed at enhancing carbon retention and sequestration through optimizing age-related stand dynamics.