Abstract: In this research three water treatment groups, including control (CK), continuous flooding (CF), and periodic flooding-drought (PF), were applied to simulate water change in the hydro-fluctuation belt of the Three Gorges Reservoir. Each group contained two plots, one planted with one-year-old slash pine (Pinus elliottii) seedlings and the other without any vegetation. We measured the pH value, and contents of organic matter (OM), alkali hydrolysable nitrogen (AN), available phosphorus (AP), available potassium (AK), total nitrogen (TN), total phosphorus (TP) and total potassium (TK) in the soil of the two plots under different water treatment. Results showed that in the condition of PF, P. elliottii soils had very significantly higher nutrient contents compared with blank soils, except for pH and AK, while soil AK contents in CK were lower than those of blank soils. Meanwhile, water treatment had significant effects on soil nutrient contents of P. elliottii seedlings except for pH, while no significant effects were found on phosphorus (P) and potassium (K) contents in the blank soil. In general, PF had the highest OM, AN, AP and TK content in the soil with P. elliottii seedlings among the three different water treatments. In addition, correlation analysis dispayed that the content of OM had a very significant positive correlation with the content of AN, TN, and TP, and there were significant or very significant positive correlations between soil total nutrient contents. The results indicated that a large amount of K was needed in the normal growth of P. elliottii, and the effects of water treatment on soil nutrient contents were effectively altered by P. elliottii seedlings. Flooding was able to promote release of soil P and K and increase the contents of AP. However, OM accumulation in the slash pine's soil was accelerated by alternate submergence and drought. If P. elliottii were planted in the riparian areas of the Three Gorges Reservoir, water eutrophication might be aggravated due to the increase of soil N and P contents.

Key words: hydro-fluctuation belt, submergence and drought alternation, Pinus elliottii seedling, soil nutrient, the Three Gorges Reservoir Area