Enhanced soil carbon sequestration capacity is facilitated by vegetation water use efficiency on Earth's Third Pole

<p>The spatiotemporal difference in water use efficiency (WUE) regulates the growth of terrestrial vegetation in alpine arid ecosystems on Earth's Third Pole, which in turn significantly affects soil organic carbon (SOC) sequestration. However, the influence of terrestrial ecosystem WUE on SOC has not been thoroughly investigated. By combining more than 2,000 soil records with long-term (1982–2013) remote sensing observations, we reconstructed three decades of historical dynamics of SOC stocks in the top 20 cm and 100 cm soil layers in Tibetan Plateau using a spatiotemporal machine learning model. The contribution of WUE to SOC stock dynamics was comprehensively deciphered. We found that SOC stocks in Tibetan Plateau exhibited an increasing trend over the past three decades (27.2–74.5 TgC yr<sup>–1</sup> across different soil layers), with WUE being the predominant factor influencing organic carbon stock dynamics. Notably, in the top 100 cm soil layer, nearly one-third of the regions showed SOC stock dynamics dominated primarily by WUE. The contribution of WUE to SOC stock dynamics varied significantly among vegetation types, with higher contributions observed in ecosystems characterized by severe water deficit. The cascaded response of SOC to environmental factors demonstrated that WUE regulates the organic carbon budgets in the top 20 cm and 100 cm soil layers by mediating vegetation growth and soil pH levels, respectively. Our findings highlight WUE as a previously overlooked factor that enhances soil carbon sequestration on Earth's Third Pole.</p>