Soil physicochemical properties of Laguncularia racemosa plantations of different stand ages in the tributary section of Nanxi, Jiulongjiang River estuary

To investigate the changes in soil physicochemical properties of Laguncularia racemosa plantations in estuarine wetlands with stand age, this study focused on three different ages of L. racemosa plantations (10 a, 12 a, and 14 a) and Phragmites australis without L. racemosa planting in the Nanxi tributary of Jiulong River estuary. Soil samples were collected using a five-point sampling method to determine soil particle size distribution, electrical conductivity (EC), pH, dissolved organic carbon (DOC), total carbon (TC), total nitrogen (TN), total phosphorus (TP), total potassium (TK), available nitrogen (AN), available phosphorus (AP), and available potassium (AK) content, respectively. The differences in soil physicochemical properties among different sampling sites were explored. Regarding physical properties, silt particles account for over 94.86% of the soil particle size composition at all sampling site. The soil EC showed considerable variation among sites, with the 14 a L. racemosa plantation exhibiting the highest EC value at 1 657.26 μS/cm, followed by 1 515.26 μS/cm, while the 12 a plantation demonstrated the lowest value at 981.51 μS/cm; In terms of chemical properties, soil pH and TP content showed a gradually decreased with increasing stand age, while TC and TN content exhibited a progressive increasing trend over time. Reed soil contained higher AK levels compared to L. racemosa artificial forest, with the lowest at 12 a forest age and the second highest at 14 a of forest age. Notably, the 12 a L. racemosa plantation soils exhibited the highest contents of DOC, AP, AN, and TK among all plantation sites. The correlation analysis between soil physicochemical properties and stand structure indicated that pH was significantly negatively correlated with TC, TK was significantly positively correlated with AP, and TN was significantly positively correlated with sand content. EC was significantly negatively correlated with average tree height, and stand density was significantly negatively correlated with canopy closure. The changes in forest age had significant effects on soil physicochemical properties. The results provide valuable data support for the scientific management of the L. racemosa wetlands and are of great significance for the ecological restoration and protection of estuarine wetlands.