Effects of vegetation type and seasonal hydrology on soil carbon and nitrogen stocks in the Dianchi Lake ecological buffer zone.

Ecological buffer zones play an important role in nutrient retention and carbon sequestration, but variation in soil carbon and nitrogen stocks among different plot types and between dry and rainy season remains insufficiently understood. Soil samples were collected from three plot types in the Dianchi Lake ecological buffer zone: Populus canadensis plots, Taxodium 'Zhongshanshan' plots, and flooded Taxodium 'Zhongshanshan' plots. Samples were taken at five depths, namely 0-15, 15-30, 30-50, 50-70, and 70-100 cm, during dry and rainy season. Soil organic carbon (SOC), total nitrogen (TN), bulk density (BD), soil water content (SWC), pH, and electrical conductivity (EC) were measured, and soil organic carbon density (SOCD) and total nitrogen density (TND) were calculated. SOC and TN generally decreased with increasing soil depth, with the highest values occurring in the 0-15 cm layer. Significant differences in carbon and nitrogen concentrations and stocks were observed among plot types, and seasonal changes were evident between the dry and rainy periods. BD was consistently negatively associated with SOC, SOCD, TN, and TND. Redundancy analysis indicated that SWC and BD were the main explanatory variables in the dry season, whereas pH and BD were more important in the rainy season. The vertical distributions of soil carbon and nitrogen differed among plot types and between season. These findings indicate that plot characteristics and seasonal conditions should both be considered in the management of lake ecological buffer zones for carbon storage and nutrient retention.