Soil dissolved carbon and nitrogen dynamics along a revegetation chronosequence of Caragana korshinskii plantations in the Loess hilly region of China

Abstract

Widespread vegetation restoration is an effective measure used to control soil erosion and improve soil organic carbon (SOC) and total nitrogen (TN) storage; however, knowledge of soil dissolved carbon and nitrogen has not been well characterized. Caragana korshinskii plantations are valued for their critical role in soil and water conservation in the Loess Hilly Region. This study aimed to estimate the levels of soil carbon and nitrogen and their dissolved fractions in one farmland (Zea mays L.) and three C. korshinskii plantations at 15, 30 and 40 years; additionally, the distribution of soil carbon and nitrogen stocks among various soil depths were estimated. The results showed that afforestation with C. korshinskii resulted in a significant increase in the contents and stocks of SOC and TN and their dissolved fractions. At a depth of 0–10 cm, the 30-year-old C. korshinskii had the highest stocks of SOC and TN, but at depths of 40–100 and 100–200 cm, the highest SOC and TN stocks were found in the soil of 15-year-old C. korshinskii. The 15-year-old C. korshinskii had the highest stocks of SOC and TN at depths of 0–200 cm and the highest stocks of dissolved nitrogen across almost all soil layers. The soil at 100–200 cm contained 34%–54% of the total percentages of the cumulative stocks of SOC and TN and their fractions. The SOC stock was the most important factor affecting the variation in soil nitrogen fractions and contributed to more than 80% of the total variation; additionally, the nitrate (NO3-N) content and stock were the most important factors affecting the soil carbon fractions, contributing to 78% of the total variation. This study demonstrates that revegetation age and soil depth play important roles in determining carbon and nitrogen levels. The results also suggest that C. korshinskii plantations should be harvested and revegetated during the rapid growth period (∼15 years) during which they show the largest accumulations of soil carbon and nitrogen.