It is time to interact: chronology and ecology in studying plant Si

Plant Si plays considerable roles in plant, animal. Ecosystem and global ecologies, including biogeochemical cycles. Understanding the ecological roles of plant Si and their evolutionary history is fundamental for increasing our understanding of this phenomenon, its origins, and its significance for past, present and future ecosystems. For these reasons, plant Si research is becoming increasingly interdisciplinary and superdisciplinary. Nevertheless, understanding the evolution of this phenomenon and its interactions with biogeochemical cycles – and furthermore understanding the implications for current and prospected environmental change – is hindered by inappropriate consideration of chronology and community ecology.

studies of the evolution of plant Si uptake, its ecology and its effects on ecosystem functioning suggest multiple types of Si-C interactions. These include – for example – Si-C tradeoffs within plants, a role of Si uptake and cycling in the C cycle (mostly C sequestration through NPP, weathering and occlusion), and Si mediating plant responses to CO₂ changes. While these suggest that plant Si may have evolved partially in response to changing CO₂ concentrations throughout the Cainozoic, implied by the contemporaneous spread of Si-rich grasslands when CO₂ levels drop. However, recent paleontological and molecular suggest no temporal match. Likewise, the possibility of Si-rich grasses and abrasion-adapted grazers is also challenged by evidence for Si having an antiherbivory role on the one hand, and lack of chronological matches on the other hand. These discrepancies may stem, in part, from two considerations that may often be overlooked, about chronology, ecology and how they connect.

First, species and their traits, as well as whole ecosystems, should be seen in the context of their entire evolutionary history, and may therefore reflect not only adaptations to extant selective forces but be anachronisms. Moreover, evolutionary history and evolutionary transitions are complex, resulting in true and apparent asynchronisms. Second, evolution and ecology are multi-scalar, in which various phenomena and processes act at various scales. In ecology, there can be great differences between how a single species responds (e.g., in monoculture) and how different responses of different species interact to shape communities, and further how changes in communities interact with other ecosystem components to shape ecosystems.

Consequently, our understanding of how plant Si may have evolved in response to CO₂ and herbivory, and how it may affect ecosystem functions such as biogeochemical cycling under current environmental changes, requires further thinking.