doi:10.1038/s41467-026-70623-9engWang, HuiMaestre, Fernando T.Lu, NanZhao, GuangZhang, YangjianAsensio, SergioBramble, De Shorn E.Chen, WeiliangDippold, Michaela A.Eldridge, David J.Gaitán, Juan J.García-Gómez, MiguelGozalo, BeatrizGross, NicolasGuirado, EmilioLe Bagousse-Pinguet, YoannMartínez-Valderrama, JaimeMendoza, Betty J.Ochoa, VictoriaPlaza, CésarSaiz, HugoSchrumpf, MarionSierra, Carlos A.Tangarife-Escobar, AndrésValencia, Enriquevon Fromm, Sophie F.Wang, CongWang, KaiWang, YunqiangZaehle, SönkeFu, BojieTrumbore, SusanHuang, JianbeiPersistence and turnover of soil organic carbon in global drylandsART-2026-149174Reliable predictions of dryland carbon fluxes require understanding the persistence and turnover of soil organic carbon (SOC). We measure radiocarbon to quantify the age of SOC and CO2 released from soil respiration at 97 dryland sites across six continents. Here we show that bulk SOC contains little C fixed in the past 60 years, while respired CO2 originates from both bomb-derived recent C and millennia-old C, challenging the idea that old C is chemically or physically protected. Radiocarbon suggests mean ages of ~2100 years for bulk SOC and ~520 years for respired CO2, the latter far older than machine-learning (<50 years) or Earth system models predict. Aridity, net primary productivity, and SOC content are dominant predictors for radiocarbon signatures, with abrupt shifts to older C beyond an aridity threshold of ~0.87. Our findings underscore the need to incorporate the vulnerability of older carbon into models and land management strategies.2026http://zaguan.unizar.es/record/17104210.1038/s41467-026-70623-9http://zaguan.unizar.es/record/171042oai:zaguan.unizar.es:171042info:eu-repo/grantAgreement/EC/H2020/647038/EU/Biological feedbacks and ecosystem resilience under global change: a new perspective on dryland desertification/BIODESERTThis project has received funding from the European Union’s Horizon 2020 research and innovation program under grant agreement No H2020 647038-BIODESERTNature communications 17, 1 (2026), [10 pp.]byhttps://creativecommons.org/licenses/by/4.0/deed.esinfo:eu-repo/semantics/openAccess