Effects of different vegetation restoration models on soil nutrients in the water level fluctuation zone of a large reservoir

• Soil nutrients decrease with the increase of reservoir inundation depth. • Natural and artificial restoration exhibit differences in soil nutrient enrichment. • Artificial restoration effectively enhances the soil TN, TP, TK, and SOC. • Restoration models influence nutrient levels in the water level fluctuation zone. Vegetation restoration is synergistic with restoring riparian ecosystems to enhance soil quality in the water level fluctuation zone (WLFZ), which is degraded by repeated inundations and cyclical fluctuations of reservoir water levels. Assessing the influence of diverse vegetation restoration strategies on soil nutrient content in the WLFZ is essential for optimizing restoration models. To evaluate the effects of different restoration approaches on soil nutrients in the WLFZ of Heilongtan Reservoir, the integrated levels of soil nutrients in similar topographical environments but with varying vegetation restoration strategies were quantitatively assessed using the entropy weight method. The results showed that reservoir water-level fluctuations significantly altered the distribution and composition of vegetation communities in the WLFZ. Inundation stress exerted a constraining effect on plant diversity, with artificial restoration strategies increasing the concentration of dominant species at the expense of overall species diversity and abundance compared with natural restoration methods. The soil organic carbon (SOC) content in the WLFZ was 77.46 % lower than that in the non-flooded areas under natural restoration conditions. However, this disparity was reduced to 23.36 % with artificial restoration, demonstrating more effective mitigation of the impact of flooding on SOC content. Inundation stress generally diminished the overall soil nutrient content, and artificial restoration resulted in higher levels of total nitrogen, total phosphorus, and total potassium by 26.04–52.53 %, 6.85–22.99 %, and 67.05–91.37 %, respectively, compared to natural restoration. Compared to the CK, the soil nutrient composite index (SNCI) exhibited a reduction of 32.09 %, whereas artificial restoration showed a significantly lower decrease of only 10.62 %. Pearson’s correlation analysis revealed that water level elevation and restoration mode were paramount factors shaping plant community diversity in the WLFZ. Notably, restoration mode emerged as a significant principal influence on SNCI variations (P < 0.05). In general, artificial restoration strategies can mitigate the detrimental effects of flooding stress on the soil nutrient dynamics in the WLFZ. The efficacy of improving comprehensive soil nutrient levels increased with the decreasing water levels. These findings highlight the potential of artificial restoration techniques as an effective means of ecological preservation in the WLFZ and contribute to the development of sustainable management strategies for this region.