Soil plant available silicon from a bamboo forest on karst mountain in southwest China differs between wet and dry seasons

The distribution and its controlling factors of soil plant available silicon (PASi) are the basis for understanding the terrestrial silicon cycle and are poorly understood in karst mountainous areas. In this study, soil PASi concentrations of <i>Dendrocalamus ronganensis</i> bamboo forest topsoil using the citric acid extraction method (citric-Si) and cave drip water Si concentrations were measured during the wet and dry seasons with the aim of understanding the relationship between available silicon and climatic variables. The citric-Si content of soils and drip water Si was in the range of 24.6–164 mg·kg⁻¹ and 3.63–13.6 mg·kg⁻¹, respectively, and decreased in the following order: A and AB horizon, O horizon, and drip water. Drip water Si was very low compared with soil citric-Si and water-soluble Si. The soil water-soluble Si and organic matter showed no significant difference between wet and dry seasons. The soil pH (KCl) and pH (H₂O) showed higher values during the wet season, and pH (H₂O) was correlated with the soil citric-Si content. The citric-Si content of soils showed variations between wet and dry seasons and was correlated positively with monthly precipitation. Drip water Si, which contributes to the loss of soil citric-Si, had no control on the soil citric-Si variation between dry and wet season. Phytoliths had a high proportion of soil dry weight, and they might be the main contributors to the DSi (soluble silicon) pool in this bamboo forest. The wet/dry seasonal difference of PASi in soils was probably linked to the dissolution of soil biogenic silicon, and precipitation altered soil water content and pH and promoted the dissolution of phytolith. This study is informative for ecological restoration and improving our understanding of silicon cycling in the karst mountain region.