The silicon cycle is known to be intertwined with the global carbon cycle, notably through the importance of silicon (Si) in the productivity of diatoms in the oceans and in the weathering of silicate minerals on the continents. Silicon is also recognized as a beneficial nutrient for plants, positively influencing their productivity and improving their resistance to herbivores and pathogens. An international collaboration led by Professor Jean-Thomas Cornelis' team from the University of Liège (TERRA Research Unit / Gembloux Agro-Bio Tech), in collaboration with the Smithsonian Tropical Research Institute (Panama), the University of Montreal (Canada), UniLaSalle-Beauvais (France) and the University of Western Australia (UWA) highlights a major change in the silicon soil-plant cycle as soils and ecosystems develop.

Based on previous research conducted at UWA by Prof. Hans Lambers on very promising adaptation in root strategies to acquire nutrients in nutrient-poor soils, Félix de Tombeur, researcher at ULiège (Terra/Gembloux Agro-Bio Tech) and first author of the article, travelled to Australia with Jean-Thomas Cornelis to better understand the silicon cycle in these extreme and unique ecosystems. "Reading the latest scientific advances in the field convinced us to go there to get a deeper understanding about the impact of the biodiversity of these ecosystems on the biogeochemical cycle of silicon", explains Félix de Tombeur. "The soil chronosequences studied is unparalleled in the world, providing a unique  in-situ experimental field, embracing two million years of soil formation thatallow us to better understand soil processes and their resulting effects on the ecosystems properties and functions " adds Jean-Thomas Cornelis.

We demonstrated that the silicon taken up by plants and precipitated in leaves to form biogenic opal structures (called phytoliths) is a major contributor to the terrestrial silicon cycle when the soil becomes almost completely depleted in inorganic minerals," says the researcher. When the leaves return to topsoil, these small siliceous structures are released as organic matter decomposes, thus replenishing the soil's silicon pool. "These phytoliths, which are much more soluble than quartz, can become an important source of available silicon in soilsfor plants. Our study also shows that, unlike the main nutrients derived from rocks, such as phosphorus, potassium, calcium or magnesium, which decrease in the soil and plants with the age of the ecosystem, silicon concentrations in plants increase continuously," adds Félix de Tombeur.

Phytoliths

"This is quite a breakthrough discovery as we show the key role played by these small silica structures in the soil, and their accumulation within plants, suggesting important implications in terms of plant protection against herbivores and insect pests within ecosystems," says Félix de Tombeur. "The study highlights all the complexity and importance of soil-plant feedbacks in the functioning of ecosystems. During our scientific venture, we did not expect such a discovery. This is even more exciting our findings confirm all the beauty of ecosystems while stressing the importance of silicon, which is often ommited in the study of the biogeochemistry of terrestrial ecosystems," concludes Jean-Thomas Cornelis.

The silicon story does not end there, since Prof. Jean-Thomas Cornelis' team has been awarded a Scientific Impulse Mandate by the FNRS in 2020 to study the effects of climate changes on soil processes controlling the silicon cycle.

Scientific reference

de Tombeur, B. L. Turner, E. Laliberté, H. Lambers, G. Mahy, M-P. Faucon, G. Zemunik, J-T. Cornelis, Plants sustain the terrestrial silicon cycle during ecosystem retrogression, Science, September 2020.