Abstract:
Ecological stoichiometry of soil aggregates provides valuable insight into the nature and extent of nutrient limitation. However, our current understanding of the nutrient distribution and ecological stoichiometry of soil aggregates and their correlations is still relatively limited. The red soils derived from red sandstone are prone to water loss and soil erosion due to the poor structure and low retention capacity of water and fertility, leading to the difficulty in vegetation recovery and soil restoration. It is necessary to explore the microscopic mechanism of nutrient dynamic during the process of erosion inferior soil restoration. Several surface (0-30 cm) soil samples were collected from the eroded badlands of red sandstone under different vegetation restoration years and types including the slash pine of 2-year and 5-year artificial restoration, the slash pine of 5-year natural restoration, the wasteland of 5- year natural restoration, and the vacant land in 6-year waxberry garden. Composition and stability of soil aggregates were determined using dry and wet sieving method. Soil micro-aggregates and mechanical composition were analyzed. Soil organic carbon (C), total nitrogen (N) and phosphorus (P) contents in the aggregates at >10, 5-10, 2-5, 1-2, 0.5-1, 0.25-0.5 and <0.25 mm sizes were determined, and the C, N and P stoichiometric ratios (C:N, C:P and N:P) were calculated. Soil anti- erodibility characteristics including aggregate destruction rate, aggregation degree, dispersion rate and water stable aggregate mean weight diameter (EMWD) were also investigated. The correlations among the ecological stoichiometry of soil aggregates, soil nutrient and anti-erodibility characteristics were further examined. The results showed that the nutrient contents in the bare land were extremely low. After the restoration under different measures, physical and chemical properties of the soils were improved. The aggregate compositions in the soils under different vegetation years and types displayed differences. The bare soil was mainly composed of >5 mm soil aggregates, accounting for more than 60% of the soils. 2-5 mm aggregate dominated in the soils from the wasteland of 5-year natural restoration. The soils developed from red sandstone under the other restoration measures were mainly composed of <0.25 mm aggregates. Soil organic carbon and total nitrogen contents in the aggregates with different sizes increased with the increasing vegetation restoration years. Soil organic carbon and total nitrogen were mainly distributed in the 0.25-1 mm aggregates, especially in the 0.5-1 mm aggregates. The evenly distribution of phosphorus in the aggregates with different sizes was observed. The destruction rates of soil aggregates under different measures decreased from 55.68% (destruction rates of soil aggregates in bare land) to 10%. The mean C:N, C:P and N:P ratios of soils in the area studied were 15.0:1, 79.7:1 and 4.0:1, respectively. Highest C:N and C:P ratios were found in the soils aggregates under the slash pine of 5-year natural restoration, but the lowest C:N and C:P ratios were observed in the vacant land in 6-year waxberry garden. It can be concluded that the soil nutrients for different eroded badlands of red sandstone increase with the increasing vegetation restoration years, and the corrosion resistance of soils has also been greatly improved. Soil nutrients are mainly distributed in the 0.5-5 mm water stable aggregate, which has been seriously lost, resulting in low soil nutrient contents and poor soil corrosion resistance. The results showed that nutrients play a restrictive role in vegetation restoration in eroded badlands of red sandstone. The results obtained by us can provide theoretical basis for soil erosion control and revegetation in eroded badlands of red sandstone.