Effects Of Simulated Nitrogen Deposition On Water-stable Aggregates And The Distribution Of C, N And P In Different Aggregate Fractions

In recent decades, the global N deposition has been significantly increased due to the fossil fuel buring and agricultural activities. Some areas have reached to nitrogen saturation and threatened sustainment of forest ecosystem functions. Soil is one of important parts in the forest ecosystems. Soil aggregates is the basic unit of soil structure and material basis for soil fertility. However, the effects of nitrogen deposition on the composition of soil aggregates have not been well examined, and this is especially true for China, where has been the third largest nitrogen deposition regions in the world. It helps to improve theoretical and practical research to investigate the effects of nitrogen deposition on forest soil carbon stability and distributions of carbon, nitrogen and phosphorus in forest ecosystems.In this thesis, we investigated the effects of 8-year-long simulated nitrogen deposition on the distributions of water-stable aggregates and concentrations of soil organic carbon, nitrogen and phosphorus in a Cunninghamia lanceolata plantation. The study site is located in Sanming, Fujian province. Nitrogen loadings was designed at 4 levels as NO (control), Nl, N2 and N3 at the doses of 0,60,120 and 240 kg·N hm-2·a-1, respectively. Bulk soil samples were separated into six aggregate-sizes (>2mm, 1～2mm,0.5～1mm,0.25～ 0.5mm,0.053～0.25mm and<0.053mm) and soil organic carbon, nitrogen and phosphorus contents were determined in those soil samples.The results showed that:(1) Nitrogen deposition did not change concentrations of soil organic carbon, but have a slight impact on soil nitrogen and phosphorus in the 0-20cm soil. (2) The highest content of water-stable aggregates was the 1-0.5mm aggregate under four treatments, which accounted for 30% of the total aggregates and was significantly higher than other particle size aggregates. (3) Compared with the control (NO), N1 and N2 treatments significantly increased the content of water-stable aggregates (>0.25mm) and the mean weight diameter of soil aggregates, but N3 treatment showed an inhibition effect. (4) Soil organic carbon distribution in different size aggregates was dominated with> 2 mm and<0.053mm aggregates. Nitrogen deposition greatly affected the distribution of organic carbon in soil aggregates Although there was no significant difference among aggregates in control (NO), the contents of soil organic carbon in the aggregates were significantly different after nitrogen deposition. For example, N2 treatment significantly increased soil organic carbon content of <0.053mm aggregates in the 0-20cm. (5) With increasing doses of nitrogen deposition, the total phosphorus content of the soil aggregates was substantially reduced. (6) Effects of nitrogen depositionon the contents of nitrogen and phosphorus of the soil aggregates were obvious in the 0-20 cm soil layer. In conclusion, nitrogen deposition would decrease stability of water-stable aggregates, resulting in the negative influence on the soil structure and nutrient losses in soil.