Comparison of topsoil organic carbon and total nitrogen in different flood-risk riparian zones in a Chinese Karst area

Riparian zones play a significant role in the soil organic carbon (SOC) sequestration to mitigate the increasing atmospheric CO₂. SOC storages vary spatially within and among riparian soils by the influence of multiple unique biotic and biophysical landscape characteristics. Understanding the distribution characteristics of SOC from the water’s edge to the upland is essential to effectively assess SOC storage and the function of carbon sink of riparian zones. In this study, the goals were to quantify the SOC density (SOCD) and total nitrogen content (TN) (0–20 cm of topsoil) in different flood-risk riparian zones of the Lijiang River [frequently flooded zones (FFz) (flood frequency ≥3 times/year), seldom flooded zones (SFz) (flood <3 times/year) and adjacent uplands (AU)], which are located in a typical karst geomorphology region, and to assess the contribution of soil texture, plant litter and soil pH to SOCD variation. The results of a soil survey of typical riparian areas (N = 15) showed that the average SOCD and TN content were 31.52 ± 13.25 Mg/ha and 0.094 ± 0.043 %, respectively, in the entire riparian zone (0–20 cm of topsoil). Compared with the SOCD in AU (19.98 ± 3.06 Mg/ha), the SOCD of FFz and SFz was significantly higher by 70.92 and 49.70 % (p < 0.05), respectively. Stepwise regression analyses indicated that soil texture was the most important factor that influenced the SOCD variation (0–20 cm of topsoil) in FFz, which could account for 67 % of the SOCD variation, while plant litter was the most important factor in SFz, which could account for 80 % of the SOCD variation. Lastly, our findings indicate that riparian zones have more SOC storages than adjacent uplands in the Lijiang River. Therefore, the exploitation of riparian zones for agricultural purposes may weaken the function of riparian on the SOC sequestration.