Background With the change of precipitation pattern under the background of global climate change, there are seasonal differences in the chemical content of throughfall and stemflow. The ion concentration of throughfall and stemflow showed a bimodal pattern, and the ion concentration was basically lower in the rainy season than in the dry season. The dry and rainy seasons in the subtropical region are distinct, which may make the chemical characteristics of precipitation in the subtropical forest canopy show seasonal differences. Based on this, this study relies on the Guangdong Nanling Forest Ecological Station to analyze the chemical characteristics of precipitation in typical forest canopy in this area, and compare the response of atmospheric precipitation chemical composition to different types of forest canopy in dry and rainy seasons.

Methods Water samples were collected immediately after the precipitation events in March, May, July 2022 and January 2023. The detection indexes were pH, TN, TP, NH₄⁺-N, NO₃^--N, Cu, Cd, Pb and Cr⁶⁺. The mass concentration and flux of chemical substances in different hydrological components of typical forest were calculated, and the difference of chemical substance concentration in different hydrological components was compared by one-way analysis of variance.

Results The results showed that the atmospheric precipitation in the dry season is acidic, and the pH value after the evergreen broad-leaved forest canopy is 6.82, and the acidity of the precipitation is buffered. The chemical input of atmospheric precipitation is mainly nitrogen and phosphorus nutrients, and the input of heavy metals only accounts for 1.19%-1.44%. The total chemical input of atmospheric precipitation in the rainy season is higher than that in the dry season, which was 4 198.4 g/hm² in the rainy season and 3 251.5 g/hm² in the dry season. In the dry season, the canopy neutralization of evergreen broad-leaved forest is better than that of the other two forests. The concentrations of chemical substances in the throughfall and stemflow of the three forests in the dry season are higher than those in the rainy season. In the dry season, the canopy of the three forest stands show leaching effect on the chemical composition of precipitation. In the rainy season, only the coniferous and broad-leaved mixed forest (having bamboo) canopy has obvious chemical leaching effect on precipitation. The leaching degree of Cu in canopy precipitation is extremely high, and the net leaching deposition ratio is between 1.22 and 16.4.

Conclusions In this study, the hydrological process monitoring of different forest communities in Nanling Mountains is carried out. However, due to the randomness of precipitation events and the great influence of complex environment in the field on hydrological observation, the conclusions obtained by using precipitation water quality data in different months need to be further observed and verified for a long time, and its internal mechanism and leaching law need to be further discussed.