Convergent evidence for temperature-dependent emergence of silicification in terrestrial plants

While research on terrestrial silicon (Si) biogeochemistry and its beneficial effects for plants has received significant attention in last decades, the reasons for the emergence of high-Si taxa remain unclear. Although the “arms race” hypothesis (i.e. increased silicification through co-evolution with mammalian grazers) has received some support, other studies have pointed to the role of environmental factors, such as high temperatures and low atmospheric CO2 levels, which could have favored the emergence of silicification. Here, we combine experimentation and analysis of existing databases to test the role of temperature on the expression and emergence of silicification in terrestrial plants. We first show through experimental manipulations of rice that Si is beneficial for growth under high temperature stress, but harmful under low temperature. We then found that, globally, the average temperature of the distribution of high-Si plants was 1.2°C higher than that of low-Si plants. Moreover, within China, a notable positive correlation emerged between the concentrations of phytoliths in wheat and rice and air temperature. From an evolutionary perspective, 65–77% of high-Si families (> 10 mg Si g− 1 DW) originated during warm geological periods, while 57–75% of low-Si families (< 1 mg Si g− 1 DW) originated during cold geological periods. On average, Earth's temperatures during the emergence of high-Si families were 3°C higher than those during the emergence of low-Si families. A correlation was also observed between the divergence of proteins related to Si transport (Lsi1, Lsi2, Lsi3, and Lsi6) and historical climatic variability. Together, cumulative evidence suggests that plant Si variation is closely related to global and long-term climate change, with potential repercussions for global Si and C biogeochemical cycles.