Objectives The vegetation in the Loess Plateau is strongly affected by hydrothermal conditions. The distribution of vegetation from the southeast to the northwest shows a zonal distribution pattern of transition from forest to grassland. Four typical vegetation belts (forest belt, forest−grass belt, grassland belt and grassland−desert belt) from the south to the north of the Loess Hilly Region were selected as the research subject to study the distribution characteristics of carbon and nitrogen in herbaceous plant leaves and soil of different vegetation belts. The results could provide a theoretical basis for predicting the growth and development of plants, plant nutrition and soil nutrient status of the ecosystem in the Loess Plateau.

Methods Fuxian County, Ganquan County, Ansai County, Jingbian County, Hengshan County, and Yuyang District of Yulin City were selected as the study areas. They are located in the loess hilly areas of Northern Shaanxi. Field sampling from four vegetation belts and laboratory analysis were conducted. The carbon and nitrogen contents of herbaceous leaves and different soil layers were measured. Finally, the differences in leaf and soil carbon and nitrogen of herbaceous plants in different vegetation belts were analyzed using variance analysis. The results were compared with global and Chinese-scale studies. In addition, four kinds of analysis were used to clarify the four species. Correlations were established between organic carbon and total nitrogen in plant leaves and different soil layers in different vegetation belts.

Results 1) The soil organic carbon and total nitrogen contents showed significant correlations in all soil layers of 0–10, 10–20, 20–40 cm (P < 0.001). In the 0–40 cm soil layer, soil organic carbon and total nitrogen contents decreased with depth. From high to low, soil organic carbon and total nitrogen contents were forest zone > forest−grass zone > grass zone > grassland−desert zone, but the vertical variation of different vegetation types varied greatly. 2) There was a significant correlation between organic carbon content and total nitrogen content in leaves of herbaceous plants (P < 0.01). The mean C content in leaves was 442.9 g/kg, which was slightly lower than the mean of 492 species of terrestrial plants which was 464.2 g/kg. The average leaf N content was 25.8 g/kg, slightly higher than the global mean of 20.6 g/kg, indicating a difference in leaf nitrogen accumulation and low herb C: N in the area. 3) Leaf C and N contents were significantly correlated with SOC and STN contents (P < 0.05). But the relationship with different soil layers was different.

Conclusions The spatial distribution of soil C and N in different vegetation belts was consistent, and there was a correlation between C and N contents. From the south to the north of the Loess Plateau, plant leaf C content decreased, while leaf N content increased, resulting in C∶N showed a decreasing trend. There was a correlation between leaf C, N, C∶N and soil C and N of different soil layers.