Distribution of soil carbon and nitrogen along a revegetational succession on the Loess Plateau of China

Changes in the natural abundance of δ13C and δ15N in soil are proposed as indicators in the evolution of ecosystems caused by land management and/or vegetational succession. Such changes are seldom known due to the lack of comparative data on the levels of δ13C and δ15N in soils. To understand the distribution of C and N during revegetational succession, we investigated the changes in the levels of δ13C, δ15N, organic carbon (OC), and total nitrogen (TN) for soils sampled from three incremental depths (0–10, 10–20, and 20–40 cm) during a revegetational succession from alfalfa (Medicago sativa, C3 plant) to the natural vegetation of bunge needlegrass (Stipa bungeana, C3 plant) in the northern Loess Plateau. The levels of δ13C and δ15N increased gradually with the succession of the alfalfa community and decreased with the succession to the bunge needlegrass community, indicating that the dynamics of the δ13C/δ15N isotopic signatures differed within the different revegetational stages of succession. A pronounced inverse relationship developed between the soil water storage (0–40 or 0–100 cm depths) and the natural abundance of δ13C/δ15N. The use of this relationship may be of value to scientists modelling nutrient cycling within different ages of vegetational succession across the semiarid regions of the Loess Plateau. Concentrations and stocks of OC and TN increased with revegetational age during the two successional stages, suggesting that revegetation enhanced the sequestration of OC and N in soils by reducing soil erosion and increasing inputs of organic materials. Our results highlight the utility of stable isotopes in studying C and N dynamics along revegetational succession on degraded land and emphasise the improvement in soil OC and N by well-managed strategies of vegetational restoration in the northern Loess Plateau.