Consistent responses of soil bacterial communities to bioavailable silicon deficiency in croplands

Soil bacterial communities play a crucial role in the maintenance of agro-ecosystem functions. Silicon (Si) fertilization has important impacts on the structure and function of soil bacterial communities. However, bioavailable Si in agricultural soils is projected to become depleted because of continuous intensive farming practices. It is urgently needed to investigate how bacterial communities respond to the Si deficiency in agricultural soils. Here, we reveal that the contents of the dissolved and reactive fractions of Si in soils have seriously decreased at the field scale. The reactive Si levels in the topsoil in rice fields (77.83 +/- 41.14 mg/kg) were lower than the reported critical limit of Si for plant growth (85 mg/kg) and therefore require special attention. We investigated the composition of soil bacterial communities in these Si-deficient soils. Most dominant bacterial phyla and their subtaxa were significantly correlated with the reactive Si content. Modules II, IV, VI, and VIII within a co-occurrence network were significantly correlated with the reactive Si content. Notably, bacterial groups related to nitrogen, carbon, sulfur, and iron cyclings significantly changed in the Si-deficient soils. Soil reactive Si showed strong direct and indirect relationships with the composition of soil bacterial communities in croplands. The findings of this study will be useful for raising awareness of the need to improve agricultural Si fertilization for agro-ecosystem health and sustainability.