Over the past three decades, plant ecologists have become increasingly interested in quantifying key plant functional traits (physical and chemical attributes with functions) and correlations between them in order to better understand how terrestrial plants allocate their resources and global plant ecological strategies. A major step was the proposition of the worldwide leaf economics spectrum (LES), which describes a universal spectrum of key leaf properties such as leaf thickness, leaf lifespan or photosynthetic rate. The spectrum runs from fast-growing species having traits associated with rapid resource acquisition to slow-growing species having traits involved in conservation of resources. This influential work on plant functional traits has provided a solid understanding of how plants allocate their resources depending on biotic and abiotic factors worldwide, and have been pivotal in plant ecology. However, although the concentrations of major soil nutrients in plants such as nitrogen (N), phosphorus (P) and potassium (K) have been incorporated in these theories, surprisingly, silicon (Si) has received no attention with regard to the LES, leading to a major gap in the literature. Yet, several elements predict a significant role of Si in the LES.
Taken up as monosilicic acid from the soil solution, Si is translocated to sites of rapid transpiration in plants, where it polymerises as amorphous hydrated silica (rock in plants!). Biosilicification has occurred in land plants for over 400 million years, and some plants can contain up to 15% of silica in their tissues. Silicon provides numerous plant benefits, especially defence against herbivores which is the best documented (no one would like to eat a sandy salad, isn't it?). In addition to leaf defence, biosilicification also provides structural support for leaves. Given the defence/support role of plant silicon, trade-offs with C-based compounds with similar functions (phenolic compounds, lignin and cellulose) have been suggested. Yet, these major roles and functions have not been considered in the context of other plant functional traits which constitutes a major gap in plant ecology, since (1) Si can accumulate in plant species in very high concentrations, (2) Si is a defence against herbivores and trade-offs exist between traits conferring fast plant growth versus those leading to plant defence, (3) plant Si strongly varies with environment, genotype, and phylogeny. Links between Si and plant ecological strategies such as the LES needs to be made to better understand the functional role of Si in terrestrial ecosystems. The project SiliConomic develops three promising research axes to build an eco-physiological understanding of the role of Si in terrestrial ecosystems, and determine its position in the LES.
(1) Test the relationships between plant Si and other key characteristics of the leaf economics spectrum along a natural gradient of soil fertility and with database
(2) Test how nutrients limitation impacts plant Si concentration and its relationship with key traits of the leaf economics spectrum
(3) Test how long-term grazing versus nutrient addition impacts plant Si concentration and other key characteristics of the leaf economics spectrum
