Silicon mobilization by leaf mass loss: Patterns with silicon condensation state

In natural ecosystems, plant species that accumulate large quantities of silicon (Si) contribute significantly to Si cycling via litterfall. However, the process of Si mobilization through changes in chemical forms during decomposition remains poorly understood. This study conducted a litter bag experiment to examine the relationship among Si condensation state, Si mobilization and leaf mass loss in Si-accumulating tropical tree species. The condensation state was expressed as Q n , where n is the number of –OSi bonds on a Si atom and decreases with increasing degradation of silica bodies. All studied species showed high leaf Si concentrations (53.6–105.2 mg g -1 leaf dry mass), with the majority of Si in Q 4 group (63–77%) followed by Q 3 (20–31%) and Q 2 (3–8%) and significant Si deposits in the epidermis. During decomposition, leaf litter Si concentration did not increase consistently across species in any of the analyzed condensation states, indicating that Si degradation is not necessarily slower than leaf mass loss. However, mass loss of highly condensed Si forms (Q 4 and Q 3 ) was positively correlated with interspecies differences in leaf mass loss, suggesting that silica bodies concentrated on the leaf surface should be degraded through the attack by decomposers. In contrast, the mobilization of Q² group could not be explained by leaf mass loss. Our findings suggest that Si mobilization during decomposition is variable among Si-accumulating species and chemical forms of Si, yet mobilization of highly condensed Si groups may depend on leaf mass loss rate.