Contrasting Silicon Dynamics Between Aboveground Vegetation and Soil Along a Secondary Successional Gradient in a Cool-temperate Deciduous Forest

Silicon is an essential or beneficial element in many organisms. Silicon uptake by vegetation strongly influences terrestrial silicon dynamics; however, little is known about the changes in plant silicon cycling during secondary succession. We hypothesized that the community-weighted mean (CWM) leaf silicon concentration changes along a secondary successional gradient because of turnover of species that differ in silicon uptake. We also hypothesized that the concentration of water-soluble soil silicon should increase with silicon input to the upper soil layer by increasing leaf litterfall. This study tested these predictions using chronosequence plots with stand ages of 16-100 years of secondary succession in a cool-temperate forest in Hokkaido, Japan. We measured the levels of leaf silicon in 36 woody species, leaf litter silicon, and water-extractable soil silicon and examined their correlations with stand age. The leaf silicon concentration varied by 17-fold from 0.6 to 10.3 mg Si g(-1), with strong phylogenetic signals among woody species. Reflecting the turnover of species and change in their abundance, the CWM leaf and leaf litter silicon concentrations increased with stand age. In contrast, water-extractable soil silicon concentration decreased despite an increase in leaf-litter silicon flux. The water-extractable soil silicon concentration was strongly and positively correlated with the soil carbon concentration, which decreased with stand age. Our results suggest that during secondary succession, forest silicon dynamics are largely associated with changes in the abundance of silicon-accumulating woody plants and soil carbon dynamics, which potentially influences other silicon-dependent organisms in the ecosystem.

Automated summary

The concentration of silicon in plants varies during secondary succession, influenced by the turnover of species with different silicon uptake capacities. The leaf silicon concentration is positively correlated with the successional stage. However, contrary to the increased leaf litter silicon flux, the concentration of water-extractable soil silicon decreases. These results suggest that forest silicon dynamics during secondary succession are mainly influenced by changes in the abundance of silicon-accumulating woody plants and soil carbon dynamics.