Carbon And Nitrogen Characteristics Of Different Plant Residues And Soils In Erosional Areas

Soil was the main reservoir of carbon and nitrogen, soil organic carbon(SOC) is a large component of the global carbon cycle. SOC plays important roles in improving soil structure, soil water holding, soil erosion and degradation, and the nutrients supply to plants. Wind and water erosion are important factors that could cause soil degradation and limits soil organic carbon accumulation wordwide. Vegetation restoration and reconstruction are used to increase the amount of plant residues which will be returned to soil. The nutrients released from the plant residues are important for plant growth and strongly linked to nutrients cycling and soil productivity in ecosystem.Therefore, eight tree species and plant residues were sampled from water-wind erosion crisscross region of the Loess Plateau of China, to determine relationships between different nitrogen forms. Meanwhile, 0~200 cm depths soils were collected from depositional and erosional sites from Belgian Loess Belt, to compare distributions and storage of soil organic carbon and total nitrogen, and to analyse their relationships between different erosional soil profiles.In addition, the stability of soil organic carbon under different oxygen concentrations conditions was studied with a soil incubation method, which used to evaluate soil ersion effects on dynamics of soil carbon, nitrogen and provided the therotical basis to evaluate the loss of soil organic carbon in different ecosystem. The main results showed as follows:1. Total nitrogen (TN) comprised 5.00% to 29.07% of total soluble nitrogen (TSN) in eight tree species and plant residues. The means of soluble organic nitrogen (SON) ranged from 0.32 to 6.24 g/kg, which were comprised 42.23% to 83.32% of TSN. Additionally, concentrations of TSN and SON both in the erect milkvetch(Astragalus adsurgens Pall.)and the alfalfa(Medicago sativa L.)were significantly higher than those in other plant residues. Correlation analysis showed that there were significant differences between TSN, SON, Inorganic N and TN in eight plant residues. It is concluded that the soluble nitrogen, especially soluble organic nitrogen is an important pool of N in the plant residues, and further research is needed to understand its role in N cycling in the plantation restoration process in water-wind erosion crisscross region of the Loess Plateau.2. Soil organic carbon and total nitrogen showed general decreasing pattern with depths at both depositional and erosional sites from Belgian Loess Belt. Soil ogacnic carbon and total nitrogen concentrations were siginificantly higher at the depositional profiles compared to erosional profiles at the comparable depths. Soil organic carbon and total nitrogen storage at depositonal sites was significantly higher than those at erosion sites in 0~50 cm soil layer. The change of C/N ratios had a general increasing trend with depths. Additionally, there was a significant difference in C/N ratios at two different sites(p<0.05). Correlation analysis showed that there was significant linear relationship between soil organic carbon and total nitrogen at two different sites(p<0.01).3. In Belgian Loess Belt, Dissoved organic carbon (DOC) conerntration at the depositional sites was significantly lower than that at the erosional sites at the comparable depths; however, there was no significant difference in Specific UV absorbance at 280 mm (UV280) between two different site(sp<0.05). The correlation analysis showed that there was no significant correlation between SOC mineralization and initial DOC contents. However, there was significant correlation between SOC and initial UV280, which showed the chemical constituents of SOC could affect SOC mineralzition.4. Adding organic substrates to soils could significantly increase the amount of SOC mineralization. The effects of oxygen concentrations on SOC mineralization were different for different soil sources. The amounts of SOC mineralization in 5~10 cm and 45~70 cm depths under 5% and 20% oxygen conditions were significantly higher compared to those in the anaerobic conditions. However, in 160~200 cm soil layers, the amount of SOC mineralization under 20% oxygen treatment was the lowest, indicating the oxgygen concentration was one of important factors that could affect SOC mineralization.