The sensitivity of rainfed agricultural crop yields to CO2 fertilization and its driving mechanisms in East Africa.

Rain-fed agriculture in East Africa faces growing threats from climate change and food insecurity. Exploring the sensitivity of major crop yields (maize, potato, sorghum, cassava) in Kenya, Tanzania, and Uganda to CO2 fertilization and its driving factors under global warming is crucial for ensuring food security. Using a CO2 time series dataset constructed from remote sensing and ground-based measurements, along with solar radiation, temperature, and NDVI data, the C-FIX model is applied to estimate gross primary productivity (GPP) from 2000 to 2021. Geographic detector is applied to analyze the driving mechanisms during the sowing, growing, and harvesting periods. The results show: (1) From 2000 to 2021, CO2 fertilization negatively impacted yields, primarily in northern Kenya and Tanzania-Uganda border regions, with the strongest effects during the growing period, particularly on potato yields (27.4 gC·m-2·month-1). (2) Potato yield is negatively affected by CO2 fertilization across all periods. Sorghum and cassava yields are negatively affected by CO2 fertilization only during harvesting period, while maize yield benefits only during the growing period. (3) Soil moisture is the primary driver of yield changes (except for cassava), with its interaction with vapor pressure deficit exerting the most significant impact across all crops. These findings highlight the critical need for effective soil moisture management and atmospheric humidity control to ensure East Africa's food security under global warming.