Soil Organic Carbon Content and Its Relationship with the Stand Age in Tea Plantations (Camellia sinensis L.) in Fujian Province, China

Optimizing soil carbon content is essential for mitigating climate change. Understanding the soil organic carbon (SOC) contents and their relationship with plantation age is important for enhancing SOC in tea plantations. However, there is still a lack of studies in quantifying the SOC–age curve of the whole life cycle in tea plantations. Thus, in this study, we collected 140 soil samples aged 3 to 60 years in the four representative regions (Anxi, Datian, Qingliu, and Fuzhou) in Fujian Province to quantify the SOC contents and their relationship with plantation age. We found that the average SOC was 14.6 ± 6.1 g/kg in the four sampling regions. Nitrogen (N) emerged as having a highly significant positive correlation with SOC (R² = 0.9). We also found a significant negative correlation between SOC and mean annual temperature (MAT) (R² = 0.6), and a significant positive correlation with mean annual precipitation (MAP) (R² = 0.6). The SOC increased with plantation age at 3–20 years old and peaked at 16–20 years old. After 35 years, the SOC decreased gradually with the aging of the plantation. The results indicated that tea plantations could be renewed after the age of 35. These results showed that optimizing age structure is important in enhancing SOC in tea plantations and is meaningful in achieving carbon neutrality.