Silicon cycling by plant and its effects on soil Si translocation in a typical subtropical area

- Biological Si cycling plays an important yet secondary role in the subtropical soil development.
- Silicate weathering dominates Si flux from the soil-plant system.
- Si cycling by plant promotes silicate weathering.
- Agricultural activities and plant species affect Si translocation and redistribution in soil.

Plants play an important role in Silicon (Si) cycling of terrestrial ecosystems. However, how plant Si is related to soil Si translocation and transformation in subtropical areas with ample weatherable silicates and agricultural activities is largely unknown. Three typical watersheds with different cropland and forest configurations in subtropical China were selected to investigate the biomass of different plant species, including coniferous forest, bamboo and paddy, as well as the geochemical composition of soil, rock, vegetation and water. The main soil types are Lithic Udorthents, Lithic Dystrudepts and Typic Epiaquepts derived from granite. Si concentrations in rock, soil, plant and water, as well as Si cycling fluxes, were measured. The results show that although a large amount of Si is cycled by plants, weathering and runoff contribute similarly to, or even more significantly than, plant cycling. High Si bio-accumulators assimilate and return more Si than low Si bio-accumulators, and also cause more phytolith-Si to be added to the surface soil, which decreases desilification rate of surface soil. Agricultural activities increase silicate weathering. Stream water Si concentrations are not affected by plant Si cycling. Thus, both agricultural activities and plant species affect Si translocation. In contrast to results from strong tropical weathering environments, Si cycling by plants in this subtropical area with abundant weatherable silicates does not dominate Si loss from soil; rather, it promotes silicate weathering and controls Si redistribution in soil profiles.