Temporal and spatial variations of soil Se in China over the past half century and its influencing factors.

Soil serves as a significant reservoir of selenium (Se) and plays a crucial role for the entry of Se into the food chain. Therefore, it is of utmost importance to gain a deep understanding of the spatial and temporal variation of total soil Se content in China, as well as its influencing factors. This understanding is essential for the rational and efficient utilization of Se resources, the maintenance of ecological balance, and the preservation of human health in the future. Through a comprehensive literature search, relevant studies were identified, and information regarding soil total Se content, soil available Se content, soil pH, and soil organic matter (SOM) was extracted. The Mann-Kendall (M-K) test was employed to analyze the variation of total soil Se content, while Moran's I was used to examine the global and local spatial clustering characteristics of soil Se. The results indicate that the total Se content in China has shown an increase at different spatial and temporal scales, particularly in Central China. Furthermore, there is a significant difference in total Se content between cultivated soil and natural soil in Central China (P < 0.05). Additionally, soil physicochemical properties have been found to impact soil total Se content. Specifically, pH is negatively correlated with soil total Se content, while SOM is positively correlated with it (P < 0.05). Overall, the findings suggest that the total Se content in Chinese soil is increasing over time, and human agricultural activities and physicochemical properties of the soil, such as soil pH and SOM, likely influence the bioavailability of Se or the overall soil total Se content through their interaction with Se speciation in the soil to some extent. It is important to note that changes in environmental conditions may also have some degree of impact on the total Se content.