Plant Silicon and Phytolith Contents as Affected by Water Availability and Herbivory: Integrating Laboratory Experimentation and Natural Habitat Studies

Abstract

Purpose When studying the effects of environmental variables on plant Si contents, results of laboratory and field experiments do not always agree with each other. However, new insights into the roles silicon plays in plant life can be gained if both approaches are integrated. Methods Experimental and natural-habitat studies of the effects of water availability and herbivory on plant silicon contents are reviewed and integrated. Results Although higher water availability is expected to have a positive effect on plant silicon contents, naturallygrowing plants often have high silicon contents when grown under drought conditions. Likewise, although experimentation suggests that herbivory has a positive effect on plant silicon contents, such a correlation is not often found in nature. Conclusions Stronger effects of multiple environmental variables or selection in favour of constitutive silicon uptake and deposition as protection from drought and grazing stresses are the reasonable causes of discrepancies between experimental and natural-habitat studies.

Silicon and Plant–Animal Interactions: Towards an Evolutionary Framework

“…Although Si accumulation in these species, its variation in response to herbivory and its conformation to herbivory hypotheses (e.g., the resource availability hypothesis) is weaker than for grasses, suggesting a weaker antiherbivory role [63], the trait may have initially evolved in some of these clades in response to herbivory during the Cretaceous [1]. At a smaller timescale, it is possible that over 5000 years of human-induced intense grazing history in the Levant has caused some grasses in this region to constitutively invest in phytolith formation, hence eliminating the positive effect of extant herbivory on their Si content [63] that is commonly observed in other parts of the world [4,5,64,65] (but see [66,67]).…”

“…Studies of herbivory effects on plant Si uptake and accumulation offer a simple example. Effects of water availability and herbivory on plant Si uptake and accumulation are more often seen and tend to be greater in controlled laboratory experiments than in field studies of naturally-growing plants [4,66]. This disparity occurs, at least in part, because naturally-growing plants are exposed to more variable sets of environmental (abiotic and biotic) conditions, whose effects on Si uptake and accumulation can confound those of a single laboratory-controlled variable.…”

“…This disparity occurs, at least in part, because naturally-growing plants are exposed to more variable sets of environmental (abiotic and biotic) conditions, whose effects on Si uptake and accumulation can confound those of a single laboratory-controlled variable. For example, the effects of herbivory on Si uptake and accumulation can be masked, in comparative studies of naturally-growing plants in different ecosystems, by climate [4,63], soil water availability [4,63,66], soil nutrient availability [66], and grazing history [63,66]. Moreover, intense millennial-scale grazing on certain species may cause them to have constituently high Si contents [63], suggesting selection in favor and fixation of high Si contents in time scales of-at least-generations to millennia.…”

“…Many plant species can take up silicon (Si) from the soil in the form of monosilicic acid (Si(OH) 4 ), and thereafter accumulate it in their tissues in various forms; mostly monosilicic acid and amorphous silica phytoliths (Si(OH) 2 •nH 2 O). This capability and the accumulated amounts are a function not only of internal mechanisms (manifested by taxonomic and phylogenetic signals in plant Si contents [1][2][3]) but also of environmental factors, including water availability, transpiration, and exposure to herbivory [4][5][6]. Si accumulation has multiple benefits to accumulating plants, protecting them from a myriad of abiotic stresses [7], pathogen intrusions [8,9], and herbivory [10,11].…”

Mycolith (fungal phytolith) morphotypes and biosilification of proteins in wood-destroying and pileate fungi

“…Their structures are resulting from the accumulation of oxalate, carbonate, or silica in cell wall or entire cell. In recent years, phytolith analysis has became valuable tool in taxonomic, palaeoenvironmental and archa eo logical work to determine the presence of species in a sample (Piperno 2006, Katz et al 2015, Zurro et al 2016. Phytoliths have been found in many plant groups (Madella et al 2005, Piperno 2006, as biogenic silica is deposited in some of tissues.…”