Identifying a suitable revegetation technique for soil restoration on water-limited and degraded land: Considering both deep soil moisture deficit and soil organic carbon sequestration

Revegetation is an important means to improve the ecosystem services delivered by degraded land; however, inappropriate revegetation can result in severe soil desiccation and ecosystem degradation in water-limited regions. Here we evaluated seven common revegetation techniques by considering both deep soil moisture deficit and soil organic carbon (SOC) sequestration on the Loess Plateau of China, attempting to identify a suitable method for soil restoration of severely degraded ecosystems. The seven revegetation techniques considered were: two single-species shrub plantations (Caragana korshinskii and Hippophae rhamnoides), two single-species tree plantations (Platycladus orientalis with terracing and Robinia pseudoacacia), and three mixed plantations (P. orientalis/H. rhamnoides with terracing, R. pseudoacacia/H. rhamnoides, R. pseudoacacia/P. orientalis). A 12-year-old abandoned cropland served as the control. The results showed that the single-species plantation of P. orientalis with terracing had the lowest soil moisture deficit in deep layers (200-800 cm) but also had the lowest SOC sequestration. In contrast, the mixed plantation of R. pseudoacacia/H. rhamnoides had the highest SOC sequestration but also had significant deep soil moisture deficit. In contrast, the mixed plantation of P. orientalis/H. rhamnoides with terracing showed near-zero deep soil moisture deficit and significant, positive SOC sequestration. Therefore, this mixed plantation was identified as representing a suitable revegetation technique for this region. The results here suggest that appropriate mixed tree/shrub plantations with appropriate land engineering measures could deliver effective soil restoration in such environments. Our results provide an insight into revegetation in areas with degraded land.