Identify a sustainable afforestation pattern for soil carbon sequestration: Considering both soil water-carbon conversion efficiency and their coupling relationship on the Loess Plateau

Afforestation is considered to be an important means to improve the ecological environment and mitigate climate change. However, inappropriate vegetation restoration can result in severe soil desiccation and ecosystem degradation in water-limited regions. Here, we evaluated the effects of six different afforestation patterns on soil moisture content, soil organic carbon (SOC) sequestration, and especially the conversion efficiency of the two on the Loess Plateau, taking abandoned land (Al) as a control sample, and attempting to recognize a suitable afforestation pattern based on these parameters. The six afforestation patterns considered were two single-species shrub plantations (Caragana korshinskii, Ck and Hippophae rhamnoides, Hr), two single-species tree plantations (Robinia pseudoacacia, Rp and Platycladus orientalis, Po), and two mixed-species plantations (Rp, Po, Pinus tabuliformis, Pt, and Ulmus pumila, Up mixed plantations (MP); Po and Pt with terracing [MP + T]). We found that mixed-species plantations (MP + T and MP) have less soil moisture depletion than single-species plantations, Ck had the highest SOC sequestration but also had a significant deep soil moisture deficit. MP + T had less deep soil moisture deficit but also had lower SOC sequestration than MP. MP show a better comprehensive effect when considering both soil organic carbon sequestration and soil water-carbon conversion efficiency. Therefore, multispecies MP represent a potentially valuable approach to sustainable afforestation patterns for soil carbon sequestration on the Loess Plateau. This afforestation pattern has the potential to be applied in other similar semi-arid and semihumid regions. Our results provide insight into vegetation restoration in areas with degraded land. In future afforestation activities, planners must alleviate regional water pressure, increase soil carbon sequestration by increasing species richness, and select the best combination of species to optimize the stability and sustainability of the plantation ecosystem.