Summary by Ryosuke Nakamura, an assistant professor at Kyoto University, Japan, working on Si cycling in the tropics.
A number of studies have shown that plants modulate silicon dynamics through their silicon uptake and return of the element to the soil via litterfall (e.g., Lucas et al. 1993; Cornelis et al. 2010). Despite this knowledge, there is limited understanding of the changes in silicon dynamics during secondary succession, a process of ecosystem regeneration following large-scale disturbances. Nakamura et al. (2023) addressed this question through a study in northern Japan. The process of secondary succession, which spans over a century, cannot be monitored in real-time. Thus, we used a chronosequence approach, which utilizes spatial variations of forest stands of varying ages, rather than temporal variations of the same stand. In previous studies of silicon dynamics, Puppe et al. (2017) analyzed the fluctuations in soil silicon pool after a ten-year period at a single site, while de Tombeur et al. (2020) employed a chronosequence approach to examine silicon dynamics over the course of two million years of soil development.
Hokkaido, a prefecture the most north of Japan, is a truly remarkable place of nature where the Tomakomai Experimental Forest, a broad-leaf cool-temperate forest, supports rich wildlife and peaceful environments for anyone who comes into contact with its beautiful nature. This forest also provides a perfect example of a chronosequence study of secondary succession (e.g., Matsuo et al. 2022). A frequent typhoon event, which typically occurs in September, creates patches of forest with different ages (~100 years). Taking advantage of this setting from young to mature forest stands, we examined how plant silicon accumulation and water-soluble soil silicon accumulation change along a secondary successional gradient over a hundred years.
We were surprised that leaf silicon concentration increased with increasing stand age. By taking account of basal area of each species occurring in the study plot, we can calculate the community weighted mean value, which is typically used to understand the response at the community level. The community weighted mean leaf silicon concentration was more strongly correlated with stand age, which implies that more silicon accumulating plants showed higher dominance at the later secondary successional stage. In contrast, water-soluble soil silicon concentration decreased with increasing stand age, and the community-weighted leaf silicon and water-soluble soil silicon concentrations were not correlated. This indicates that species turnover plays a key role in modulating silicon uptake during secondary succession.
This study has implications in multiple areas. What would be an ecological impact of increasing silicon accumulation toward the later successional stage? For instance, silicon may not be merely a cheap substitute for carbon, and the underlying mechanism should be further examined (de Tombeur et al. 2022; Hodson and Guppy 2022). Also, if silicon dynamics in the plan-soil system change during secondary succession, what would be the impact on silicon dynamics at the watershed scale? Increasing silicon uptake may decrease silicon flux to the aquatic environment (e.g., Cornelis et al. 2010; Carey and Fulweiler 2012). Finally, the reproducibility of these results in other forest ecosystems remains to be seen. Further research is required to gain a comprehensive understanding of the general pattern of silicon dynamics during secondary succession.
Enjoyed the blogpost? Read the full paper at:
Nakamura, R., Watanabe, T. & Onoda, Y. Contrasting Silicon Dynamics Between Aboveground Vegetation and Soil Along a Secondary Successional Gradient in a Cool-temperate Deciduous Forest. Ecosystems (2023). https://doi.org/10.1007/s10021-022-00816-y
Study site
Tomakomai Experimental Forest, Hokkaido University
Photo 1: The breathtaking landscape of Tomakomai Experimental Forest captured from a research crane (25-m tall) which facilitates studies on plant ecophysiology and entomology in the canopy ©Ryosuke Nakamura
Photo 2: Patch formation of varying forest stand ages resulting from historical typhoon events ©Ryosuke Nakamura
Photo 3: The fauna of the forest – a male deer spotted during fieldwork ©Ryosuke Nakamura
Siliceous Plants 