Lengthening vegetation carbon turnover time across China's forests.

Vegetation carbon turnover time (τveg) dominates the uncertainty in terrestrial carbon cycle dynamics. Reports have shown that the τveg 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 τveg in widespread younger forests, which exhibit different growth patterns, remains inconclusive. Here, we consistently revealed a significant overall increase in τveg (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 τveg. The effects of forest age on τveg dynamics and the high sensitivity of enhanced carbon sinks to τveg should be incorporated into future land surface models to ensure that the τveg 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.