[Spatial Variation of Soil Organic Carbon and Stable Isotopes in Different Soil Types of a Typical Oasis].

Soil organic carbon (SOC) and its stable isotope composition reflect important information on ecosystem carbon cycle. Under the background of global change, it is of great significance to study carbon dynamics and sustainable development of carbon resources in terrestrial ecosystems. In this study, four soil types in Alar oasis were studied to determine SOC content and δ13 C value at different layers, and the differences of δ13CSOC abundance and its relationship with soil environmental factors were also discussed. Three main outcomes were drawn from the results. ①The total organic carbon (TOC) content of the soil was in the order of irrigated desert soil > brown desert soil > saline soil > aeolian sandy soil, and had a higher value in the surface layer (0-20 cm layer); δ13CSOC ranged from -26‰--23‰, the surface layer (0-20 cm) was in the order saline soil > aeolian sandy soil > irrigated desert soil > brown desert soi. ② Both SOC and δ13CSOC were significantly affected by soil type and their interaction, and by soil depth. Furthermore, the effect test of interaction indicated that SOC was significantly impacted by environmental factors, but the impact on δ13CSOCwas relatively weak. ③ The results of redundancy analysis showed that SOC had a significant or extremely significant positive correlation with soil inorganic carbon, total nitrogen, soil water content and bulk density, and had a significant negative correlation with C/N. There was also a significant positive correlation between δ13CSOC and conductivity, and in addition, δ13CSOC was negatively correlated with soil inorganic carbon and soil water content. The analyses showed that SOC and its isotopes changed with soil types, and that the effect of soil type was stronger than that of soil depth, which was mainly determined by soil moisture content.

[Correlation Between Soil Organic and Inorganic Carbon and Environmental Factors in Cotton Fields in Different Continuous Cropping Years in the Oasis of the Northern Tarim Basin].

Studying the characteristics of soil organic carbon (SOC) and soil inorganic carbon (SIC), and their relationship with environmental factors is helpful for understanding soil ecological processes, and providing theoretical support for research on the global carbon budget. Based on the oasis in the northern margin of Tarim Basin, this study analyzed the characteristics of the soil carbon pool, and, combined with redundancy and path analyses, explored the relationship between SOC and SIC, and their environmental factors. The results showed that there was a significant difference (P<0.05) in SOC and SIC contents in cotton fields with different continuous cropping years (P<0.05). With an increase in continuous cropping years, the SOC content increased firstly and then decreased, while the SIC content decreased firstly and then increased (P<0.05). The SOC content was the highest in the 0-20 cm layer, while the SIC content was the highest in the 20-50 cm layer. The importance of environmental factors on the characteristics of the soil carbon pool was deduced by redundancy analysis. The order of importance was phosphatase activity > pH > sucrase activity > catalase activity > total N > available P > available K > soil moisture content > urease activity > electrical conductivity (EC); phosphatase activity, pH value, invertase activity, catalase activity, total nitrogen, available phosphorus, and available potassium showed significant correlation with SOC and SIC (P<0.01). Soil moisture and urease activity showed significant correlation with SOC and SIC (P<0.05). The path analysis showed that available P had a direct effect on the SOC content; it was the main factor affecting it. The urease activity had a direct effect on SIC; it was the main factor affecting it. This study of soil carbon pools in arid and semiarid regions is the basis for evaluating the "source/sink" effect of soil carbon in farmland ecosystems, and is of great significance for studying the global carbon budget and land carbon cycle mechanism.

[Soil Organic Carbon Components and Their Correlation with Soil Physicochemical Factors in Four Different Land Use Types of the Northern Tarim Basin].

In order to clarify the distribution of each component of soil organic carbon (SOC) in arid areas, and to develop methods to rationally solve problems caused by inefficient land use and blind tillage, we studied the effects of different land use patterns on the SOC, microbial biomass carbon (MBC), dissolved organic carbon carbon (DOC), and easily oxidized organic carbon (EOC) on four different land use types: saline soil, natural forest, sandy land, and 30 a cotton field in the northern Tarim Basin. The relationships between different carbon components and soil physicochemical factors were researched by redundancy analysis (RDA). The results showed that the SOC showed the highest value (1.92 g·kg-1) in natural forests and increased with soil depth, while the other land use types showed a downward trend as a whole. The MBC showed the highest level in natural forests, and decreased with soil depth, but there was no obvious change trends in other land use types. The highest and lowest DOC contents appeared in the 80-100 cm layer (143.23 mg·kg-1 and 30.00 mg·kg-1, respectively) in the natural forest and 30 a cotton field, respectively, and increased with soil depth in the natural forest (P<0.05). In the saline soil, the DOC content of the soil decreased with increased depth, and the contents of different soil layers showed significant differences (P<0.05). The EOC content did not show a obvious regularity in different soil layers of different land use types. Sensitivity analysis of each organic carbon component showed that the MBC was the most sensitive to soil layer changes, and the DOC was the most sensitive to different land use patterns. The MBC has a certain indication of soil layer change, which may be due to the fact that microbial biomass C in different layers has different living environments, so the content was significantly different. The DOC has a certain indication of land use types change, which may be due to the adaptation to different situations. Through the RDA, it was found that there was a positive correlation between soil components and soil water content (SWC), total nitrogen (TN) and pH, and a negative relationship between bulk density (BD) and electrical conductivity (EC). The order of importance of environmental factors to the contents of carbon components is as follows: BD > SWC > EC > TN > pH. This indicates that bulk density and water content are the main factors affecting organic carbon components in arid regions.

[Transfer of Soil Organic Carbon to Inorganic Carbon in Arid Oasis Based on Stable Carbon Isotope Technique].

The northern margin oasis of the Tarim Basin in the central arid region of Asia was selected as the study area. The study analyzed the δ13C values of the SIC(soil inorganic carbon) and distinguished the pedogenic carbonate in soil from the total SIC using the stable carbon isotope techniques and models. Based on the relationship between soil organic carbon and inorganic carbon contents in soil, the transfer of SOC to SIC was discussed. The results showed that the δ13C values of the SIC of 4 types of arid oasis soil were significantly different (P<0.01), the δ13C values of the SIC of aeolian sandy soil was (0.32±0.04)‰, which increased with increase in depth. This indicates that the lithogenic carbonates of the sandy soil are advantageous. The δ13C values of the SIC of irrigated desert soil, brown desert soil, and saline soil were (-0.30±0.24)‰, (-1.96±0.66)‰ and (-1.24±0.49)‰, respectively, and decreased with increase in depth. This indicates that the lithogenic carbonates dominated the irrigated desert soil, and the pedogenic carbonates dominated brown desert and saline soils. In the aeolian sandy, irrigated desert, brown desert, and saline soils, pedogenic carbonate accounted for 1.33%, 4.72%, 15.01%, and 35.71% of SIC, respectively, which were less than 50%. This shows that the level of soil pedogenic carbonates was low in arid oasis. During pedogenic carbonate formation or recrystallization, the aeolian sandy, irrigated desert, brown desert, and saline soils fixed 0.30, 2.44, 4.96, and 12.40 g·kg-1 of soil CO2, respectively, the average amount of CO2 fixed from the atmosphere was 0.18, 0.79, 1.45, and 8.67 g·kg-1, respectively. Furthermore, the transfer of SOC to SIC was 0.06, 0.83, 1.62, and 1.86 g·kg-1, respectively. The total transfer of SOC to SIC was between 0.03 and 2.38 g·kg-1, with an average of 1.09 g·kg-1 of CO2. This shows that the proportion of soil pedogenic carbonates and the contribution of SOC were not high in the arid oasis area.