Nitrogen addition increases aboveground silicon and phytolith concentrations in understory plants of a tropical forest

Purpose Silicon (Si) is a beneficial element for
plants and plays important roles in the biogeochemical cycle of mineral
elements.
Yet, few studies have focused on the impact of nitrogen (N) deposition on
plant Si uptake and the Si biocycle.

Methods We designed an experiment dealing with canopy and understory N
addition in a tropical forest to comprehensively assess the response of Si
cycle to N addition focusing on understory plants and topsoil. After six years of treatment, we compared the effects of different treatments
on the concentrations of Si-related variables in the leaves of dominant
understory species, and topsoil. The foliar elemental stoichiometry, plant water-use efficiency, and soil properties were also assessed to explore
potential mechanisms underpinning an N-regulated biological feedback loop of
Si.

Results The concentrations of SiO2 and
phytolith in the leaves of the understory plants increased under N addition,
while those of phytolith and plant-available Si in the topsoil were not
altered. The significant accumulation of Si in the leaves and the unaltered
plant-available Si concentrations in the soil were associated with enhanced
plant Si uptake and decreased soil phytolith return due to increased phosphorus
(P) limitation, soil acidification, and decreased
leaf C:N ratios caused by N addition.

Conclusion Our findings suggest that N addition affected plant
phytolith production and its coupling with the Si biocycle in the forest which may
stimulate plant Si accumulation and decrease soil Si return. Nitrogen
enrichment will alter the biological Si cycle in forest ecosystems at regional
and global scales.